Search

The semi-solid slurry preparation process, microstructure, and mechanical properties of truck coarse filter bracket were studied in this paper. The semi-solid aluminum alloy slurry with high solid fraction was prepared by the Slurry Enthalpy Equilibrium Device (SEED) method, and the optimum slurry preparation parameters were determined through the observation and analysis of the slurry microstructure as follows: pouring temperature 700 °C, rotation speed 180 r/min, and crucible temperature 400 °C. The average grain size and shape factor of the slurry prepared under these conditions are 50.448 μm and 0.799. Die casting trial production which used the best process parameters of slurry preparation and die casting was carried out. The results show that the die casting parts are completely filled with no obvious surface defects. It can be seen from the cutting experiment and X-ray non-destructive test that the internal structure is dense and uniform, and there are no obvious casting defects that were observed such as cracks and holes. The semi-solid die castings were strengthened by T6 heat treatment. The experimental results showed that the optimal heat treatment parameters were a solution temperature of 470 °C and time of 4 h, aging temperature of 175 °C and time of 12 h. Under these conditions, the microstructure morphology was improved significantly. The tensile strength and yield strength reached 342.1 MPa and 309.1 MPa, respectively, which were 38.9% and 95.3% higher than the semi-solid state, and the elongation was 4.5%. [ABSTRACT FROM AUTHOR]

We employed a melt ultrasonic treatment near the liquidus to prepare a high-thermal-conductivity Al-4Si-2Ni-0.8Fe-0.4Mg alloy. The influences of various ultrasonic powers on its microstructure, mechanical properties, and thermal conductivity were investigated. It is shown that near-liquidus ultrasonication significantly refines the alloy grains and eutectic structure, synergistically improving the alloy's mechanical properties and thermal conductivity. Specifically, the grain size decreased by 84.5% from 941.4 to 186.2 µm. Increasing the ultrasonic power improved the thermal conductivity of the alloy slightly and significantly enhanced its mechanical properties. At an ultrasonic power of 2 100 W, the tensile strength, yield strength, elongation rate, and thermal conductivity were 216 MPa, 142 MPa, 6.3%, and 169 W/(m·k), respectively. [ABSTRACT FROM AUTHOR]

Al–Nb–B refiner has been considered as an alternative to Al–Ti–B refiner for hypoeutectic Al–Si alloys due to Si-poisoning effect. In this paper, the effects of Al–Nb–B and Al–Ti–B refiner on the microstructure and mechanical properties in indirect squeeze casting Al–8Si-0.2Mg-0.5Mn alloy were compared. Results show that the grain sizes in the edge chilling layer, segregation band, and the center region of the Al–Nb–B refined alloys were refined by 13.9%, 12.5%, and 17.6% compared to Al–Ti–B refined alloys, respectively. The yield strength, tensile strength, and elongation of Al–Nb–B inoculated alloys were superior to those of the unrefined alloys and Al–Ti–B inoculated alloys. The coexistence of NbAl3 and NbB2 particles in the Al–Nb–B refiner exhibited excellent anti Si-poisoning capability. They significantly decreased the grain size and uniformly distributed the eutectic Si particles and Fe-rich phases, resulting in an increase in the yield strength of the alloy by 16.1% compared to the Al–Ti–B inoculated alloy. The distribution of iron-rich phases in the segregation band was affected by the inoculation. The size of α-Al15(Fe, Mn)3Si2 phase in Al–Ti–B inoculated alloys was refined, and the number significantly increased, resulting in a decrease in tensile strength of 12.82 MPa. In the Al–Nb–B inoculated alloys, the size and number of α-Al15(Fe, Mn)3Si2 phase decreased, and the δ-Al4FeSi2 phase increased, which effectively improved the fracture toughness and ductility. In addition, with the increase in grain refinement (from unrefined to Al–Ti–B to Al–Nb–B inoculated alloy), the fracture behavior changed from trans-granular fracture to intergranular fracture, improving the fracture toughness.

Near-eutectic Al–Si alloys attracted significant interest in automotive, aerospace, and other industries owing to their superior strength and high-temperature resistance. However, the alloy's narrow solid–liquid temperature range presents challenges in semi-solid processing. In this study, an Enclosed Cooling Slope Channel was used to prepare near-eutectic Al–12Si–4Cu–2Ni–0.8Mg–0.1Gd alloy semi-solid slurry. We investigated the impact of liquid squeeze casting (LSC) and rheo-squeeze casting (RSC) on the alloy's microstructure characteristics and properties of the alloy were explored. Findings indicate that the average size of primary α-Al decreases first and then increases with the rising pouring temperature. Through the RSC process, the ultimate tensile properties of the material are significantly improved, achieving optimal tensile properties at the pouring temperature of 605 °C, with ultimate tensile strength and elongation of 247 MPa and 2.66%, respectively. Compared with LSC samples, the ultimate tensile strength and elongation increased by 44.4% and 116.3%, respectively. This enhancement in properties is credited to the notable reduction in porosity and the spheroidization of primary α-Al. Regarding high-temperature performance, the alloy's tensile strength at a test temperature of 200 °C stands at 194.6 MPa. marking only a only 21.2% decrease from the room temperature result. The precipitation of the thermally stable phase and the solid solution effect of Gd elements effectively hindered the reduction of high-temperature tensile properties. [ABSTRACT FROM AUTHOR]

Based on previous work, where Al-Si-Cu-Ni alloy was successfully manufactured by laser powder bed fusion (PBF-LB/M) technology, in this study, we further observe the microstructure of the alloy, analyze the formation mechanism of the microstructure during solidification, and discuss their implications for the mechanical properties. The results indicate that the microstructure comprises multi-level cellular heterogeneous structures, with an α-Al matrix in the interior of the cellular structure and Cu- and Ni-rich phases clustered at the boundaries, intertwined with the silicon network. During solidification, α-Al solidifies first and occupies the core of the cells, while Si phases and Cu- and Ni-rich phases deposit along the cellular boundaries under the influence of surface tension. During the solidification process of cellular boundaries, influenced by spinodal decomposition and lattice spacing, Si phases and Cu- and Ni-rich phases interconnect and distribute crosswise, collectively forming multi-level cellular structures. The refined cellular microstructure of the PBF-LB/M Al-Si-Cu-Ni alloy enhances the mechanical properties of the alloy. The alloy exhibits a bending strength of 766 ± 30 MPa, a tensile strength and yield strength of 437 ± 6 MPa and 344 ± 4 MPa, respectively, with a relatively low fracture elongation of approximately 1.51 ± 0.07%. Subsequent improvement can be achieved through appropriate heat treatment processes. [ABSTRACT FROM AUTHOR]

In this study, the friction surfacing of Al–16Si alloy on AA1050 substrate was investigated using experimental and smoothed-particle hydrodynamics simulation methods. The effect of Al–16Si rod rotational speed on microstructure, surface roughness, mechanical properties, and wear resistance of coatings was examined. Both experiment and simulation findings show that by enhancing the rotational speed from 600 to 1000 rpm while reducing the effective width and thickness of the deposited layer, the deposited layer's efficiency decreases from 41 to 14%. By increasing the rotational speed from 600 to 1000 rpm, the interface roughness and surface roughness decreases to 78 and 80%, respectively. According to experiment and simulation results, plastic strain's influence on the grain size is dominant at a high rotational speed (1000 rpm), and by decreasing the rotational speed down to 600 rpm, the effect of temperature is dominant. In addition, the distribution of CuAl2 and silicon particles become more uniform with a decrease in the rotational speed from 1000 to 600 rpm, and the average size of these particles decreases to 0.62 and 4.35 μm, respectively. Compared to the pure aluminum substrate, surfacing with a rotational speed of 600 rpm increases hardness, shear strength, and wear resistance by 224%, 265%, and 60%, respectively. [ABSTRACT FROM AUTHOR]

The effect of Y content on the microstructure of A356 aluminum alloy and the mechanical properties of the alloy under T6 heat treatment was investigated. The results show that with the addition of 0.3 wt.% rare earth Y, the grain size of the cast A356 aluminum alloy reaches a minimum and the mechanical properties reach an optimum. After the T6 heat treatment, the grain structure of the alloy was further reduced and the mechanical properties were further improved. Compared to the cast A356 aluminum alloy without Y, the average α-Al grain size is reduced by 53.4%, the secondary dendrite SDAS by 32.2% and the average length of eutectic Si particles by 82.0%. The ultimate tensile strength (UTS) and elongation (El) increased to 280.75 MPa and 14.43% respectively, and the Vickers hardness increased to 102.9 HV. [ABSTRACT FROM AUTHOR]

The effects of Al-5Ti-1B and Sr on the microstructure and properties of ZL101 alloy were studied, and the degree of eutectic Si modification was evaluated by solidification behavior. The results show that Al-5Ti-1B has a great effect on the refinement of primary α-Al dendrites, Sr has a great effect on the modification of eutectic Si, Al-5Ti-1B and Sr have a significant effect on the refinement of α-Al, and most of the eutectic Si is transformed from coarse lamellar to fine fibrous, but an incompletely modified region appears. Thermal analysis shows that the degree of undercooling in the primary α-Al and the nucleation rate is increased by the combined addition of Al-5Ti-1B and Sr, the effect of grain refinement is good, and the growth temperature of eutectic Si in the precipitation stage increases, and the metamorphic effect decreases slightly. More importantly, compared with the unmodified alloy, the alloy with Al-5Ti-1B and Sr addition combined increased the hardness by 9.8% and the electrical conductivity by 8.9%. The influence mechanism of the interaction between Al-5Ti-1B and Sr on the microstructure and properties of the alloy is discussed. [ABSTRACT FROM AUTHOR]

The printability of Al6SiMg0·5Er1·0Zr alloy at various laser power, scan speed, and hatch spacing was investigated. The optimal processing window was determined. The relationship between hatch spacing and lack of fusion (LOF) defects and microstructure is discussed. Hatch spacing significantly affects the cellular size, which is formed by eutectic Si network, and medium hatch spacing can achieve the finest microstructure. Samples with high densities and fine microstructures were investigated more carefully. The grain and cellular boundaries have many Al3(Er,Zr) phases. The grain size was refined to 2.64 μm, and the epitaxial growth of columnar crystals was completely suppressed. The cellular structure has been significantly improved. Get the equiaxed - ultrafine equiaxed - columnar multi-cellular structure with dramatically enhanced mechanical properties. The yield strength, tensile strength, and elongation were 373 Mpa, 480 MPa, and 5.5%, respectively. Grain boundary strengthening and Orowan strengthening was the main strengthening mechanisms.

This paper investigates the effect of different casting conditions on the microstructure of Al-7Si-0.4 Mg alloys with 0.3 wt.% rare earth Y addition and the effect of T6 heat treatment on their mechanical properties. The experimental studies showed that the addition of 0.3 wt.% rare earth Y at 30 min or 1200 k resulted in the optimum microstructure and mechanical properties of the alloys, and the addition of Y led to the formation of Y-containing nanoparticles on eutectic Si, which were re-solidified by T6 heat treatment and precipitated a more stable orthorhombic cubic structure of Al2Si2Y compounds at the grain boundaries. According to the growth kinetic relationship, the addition of Y replaces the nucleation center of the original eutectic Si, and the preferential precipitation of the Y-containing phase destroys the heterogeneous nucleation conditions of the original eutectic Si, which leads to the growth of eutectic Si towards the original growth direction close to 60°, and generates more heterogeneous twins at the interface and gradually builds up, which has an inhibitory effect on the growth of eutectic Si. The fracture morphology and energy spectra show that the precipitated Y-containing coexist in these precipitates will lead to local stress concentration resulting in microcracks and ultimately fracture, which will change the mechanical properties of the alloy significantly.

The Light Engineering Sector (LES) is regarded as the bloodline of Bangladesh’s economy for simultaneously creating jobs, poverty alleviation, and strengthening foreign currency reserves by reducing dependency on imported products for local industries. But this promising industry is now facing roadblocks mainly due to poor quality under service loading. Though many new and advanced manufacturing techniques are now available, conventional sand casting is the most widely used manufacturing technique utilized by the local spare parts manufacturer. It is well established that the mechanical properties (strength, toughness) of a material are determined by its microstructure. To date, the microstructure characterization of LES products has not been subject to much scrutiny. Therefore, in this work, an attempt has been made to systematically investigate the microstructure of an LES-manufactured marine propeller using an Optical microscope (OM) and Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS). A locally made marine propeller supplied by ACBD company was used for this study. It was found that the microstructure of both materials mainly consists of pores, needle-shaped particles, and Chinese script-like features embedded in the aluminum matrix. Based on EDS results it may be concluded that the needle-shaped particle is mainly composed of Si and Al. Moreover, the average pore size observed was about 5109.5 μm. Use of horse-and-buggy technology, and lack of knowledge of the casting process such as properties of molding sand, the composition of raw material, overall metallurgical control of the casting process, etc. might have resulted in these casting defects. As the conventional particle fracture mechanism for ductile fracture starts once the maximum load is applied, the presence of pores may exhibit premature growth soon after the beginning of plastic deformation. Therefore, the presence of large pores may exhibit premature growth immediately at the beginning of plastic deformation, thereby drastically reducing the mechanical properties under service loading. In summary, both the government and the private sector should involve themselves in strong and focused dissemination research activities with the support of universities so that suitable modifications and modernization can be adopted in the existing system.

The laser powder bed fusion (L-PBF) process provides the cellular microstructure (primary α phase surrounded by a eutectic Si network) inside hypo-eutectic Al–Si alloys. The microstructure changes to the particle-dispersed microstructure with heat treatments at around 500 °C. The microstructural change leads to a significant reduction in the tensile strength. However, the microstructural descriptors representing the cellular and particle-dispersed microstructures have not been established, resulting in difficulty in terms of discussion regarding the structure–property relationship. In this study, an attempt was made to analyze the microstructure in L-PBF-built and subsequently heat-treated Al–12Si (mass%) alloys using the persistent homology, which can analyze the spatial distributions and connections of secondary phases. The zero-dimensional persistent homology revealed that the spacing between adjacent Si particles was independent of Si particle size in the as-built alloy, whereas fewer Si particles existed near large Si particles in the heat-treated alloy. Furthermore, the first principal component of a one-dimensional persistent homology diagram would represent the microstructural characteristics from cellular to particle-dispersed morphology. These microstructural descriptors were strongly correlated with the tensile and yield strengths. This study provides a new insight into the microstructural indices describing unique microstructures in L-PBF-built alloys. [ABSTRACT FROM AUTHOR]

The effects of Fe, Cr and thermal exposure on the microstructure and mechanical properties of Al-Si alloy were investigated in this work. The results indicated that the main phases of the Al-Si-Cu-Ni-Mg-(0.6–0.9%) Fe (wt. %) alloy were α-Al, Si, Al5Cu2Mg8Si6, Al3CuNi, Al7Cu4Ni, Al2Cu, and AlFeSi at room temperature. The size of the AlSiFe phase increased with increasing the weight fraction of Fe. The shape of Fe-rich phase changed from rod-like to star-like, followed by long needle-like with Fe varying from 0.6% to 0.9%. The mechanical properties of the studied alloys at elevated temperatures increased with Fe. The ultimate tensile strength of the three alloys at 350 °C was 111.2 MPa, 124 MPa, and 128.7 MPa, respectively. In addition, the ductility and strength of the studied alloys at room temperature decreased with increasing the Fe, due to the large size of the hard and brittle Fe-rich phase strictly cleaved the aluminum matrix. After thermal exposure, the properties of the alloy at room temperature and elevated temperature decreased obviously at the beginning of 0.5~8 h, and then tend to be stabilized during thermal exposure at 350 °C for approximately 32~64 h. Fe-rich was a thermal stable phase at 350 °C. [ABSTRACT FROM AUTHOR]

To investigate the low-cost and short-process recycling technologies for aluminium alloys, recycled chip-based Al-Si-Cu-Fe alloys were fabricated by spark plasma sintering (SPS) and hot extrusion. Microstructural observations by optical microscopy and scanning electron microscopy indicated that the recycled alloys could achieve good metallurgical bonding between the chips by fragmenting the alumina films on the chip surface by spark plasma sintering and hot extrusion after hot compress. The hot extruded recycled alloy has a smaller matrix grain size and second phase size than that of spark plasma sintered recycled alloys, due to the dynamic recrystallization and fragmentation of strong plastic deformation that occurs during the hot extrusion process. As a result, the chip-based Al-Si-Cu-Fe alloy recycled by hot extrusion after hot compress exhibited the best mechanical properties, with ultimate tensile strength, yield strength, and elongation of 258 and 132 MPa, and 8.6 % than that recycled by spark plasma sintering because of the effective metallurgical bonding between the chips, refinement of matrix grains, fragmentation and dispersion reinforcement of the oxide film and the second phase. [ABSTRACT FROM AUTHOR]

Al-Si/7.5 wt.%Y2O3 coatings were prepared on Mg alloy with laser cladding to enhance the wear and corrosion resistance of substrate. The influence of laser power on the microstructure and properties of the coating were discussed. The results uncovered that the coatings consisted primarily of Mg2Si, Mg17Al12, Mg2Al3, Al4MgY, and α-Mg phases. Through calculation, it was observed that the crystal size decreased with the decrease in the laser power. Y2O3 gave the coating a better strengthening effect due to the fine-grain strengthening and hard-phase strengthening. The average hardness of the coating with laser power of 1100 W achieved 312 HV, which was approximately 4.2 times that of the substrate. The wear volume of the coating was 22.2% that of the substrate. Compared with Mg alloy, the self-corrosion potential of the coating increased by 1.09 V, and the self-corrosion current density decreased by three orders of magnitude. [ABSTRACT FROM AUTHOR]

Based on previous work, where Al-Si-Cu-Ni alloy was successfully manufactured by laser powder bed fusion (PBF-LB/M) technology, in this study, we further observe the microstructure of the alloy, analyze the formation mechanism of the microstructure during solidification, and discuss their implications for the mechanical properties. The results indicate that the microstructure comprises multi-level cellular heterogeneous structures, with an α-Al matrix in the interior of the cellular structure and Cu- and Ni-rich phases clustered at the boundaries, intertwined with the silicon network. During solidification, α-Al solidifies first and occupies the core of the cells, while Si phases and Cu- and Ni-rich phases deposit along the cellular boundaries under the influence of surface tension. During the solidification process of cellular boundaries, influenced by spinodal decomposition and lattice spacing, Si phases and Cu- and Ni-rich phases interconnect and distribute crosswise, collectively forming multi-level cellular structures. The refined cellular microstructure of the PBF-LB/M Al-Si-Cu-Ni alloy enhances the mechanical properties of the alloy. The alloy exhibits a bending strength of 766 ± 30 MPa, a tensile strength and yield strength of 437 ± 6 MPa and 344 ± 4 MPa, respectively, with a relatively low fracture elongation of approximately 1.51 ± 0.07%. Subsequent improvement can be achieved through appropriate heat treatment processes.

The effects of mixing temperature, i.e., the temperatures of two precursor melts (pure Al and Al-12Si), on the temperature and solute fields of resultant mixture, the nucleation and growth, and the size and morphology of primary grains during controlled diffusion solidification (CDS) of Al-8Si alloy were investigated by using simulation and calculation. The results indicate that a lower mixing temperature is helpful for achieving more supercooled microscale Al-rich pockets in the mixture, and increasing the width and supercooling degree of supercooling zone in the Al-rich pockets, and thus, the nucleation rate. The nuclei grow up in nondendritic mode, resulting in spheroidal, at least, nondendritic grains. In a successful CDS, the superheat degrees of the two precursor melts should be limited within several degrees, and it is not necessary to extra stipulate the superheat degree of target alloy melt (Al-8Si) when the requirement about Gibbs energies of the three melts is matched. Subsequent observation on casting microstructures shows that the employed simulation and calculation processes are reasonable and the achieved results are reliable. [ABSTRACT FROM AUTHOR]

The wear behaviour of the Al-7Si alloy was investigated in this study under various in situ TiB2 reinforcements (3, 5, and 7 wt%). These composites were made by reacting molten Al-7Si alloy with a combination of KBF4 and K2TiF6 at an 800 °C reaction temperature. Stir casting was used to evenly distribute TiB2 reinforcing particles in the Al-7Si alloy. The microstructure, worn surface, and phases of both matrix and composites were described using an optical microscope (OM), scanning electron microscopy (SEM), and EDS, respectively. The findings reveal the presence of a dendrite Al phase and a needle shape of eutectic Si phase in matrix alloys. The microstructure of the composites reveals homogeneous dispersion of TiB2 particles, grain refined Al, and eutectic Si phase in a short-rod shape. With an increase in TiB2 concentration, there was significant refinement in Al and a reduction in interspaced between eutectic silicon. The microhardness of base and composites containing various amounts of TiB2 was investigated. It was observed that the hardness of composites increases as the weight % of TiB2 increases when compared to matrix alloy. When compared to matrix alloy, the Al-7Si -7TiB2 composite had a nearly 45% higher hardness. Dry sliding at loads of 10, 20, 30, and 40 N with sliding velocities of 1, 2, and 3.0 m/s was used to investigate the wear characteristics of the base alloy and composites.. The wear rate was shown to decrease under all operating settings with greater TiB2 concentration, according to the findings. Abrasion and de-lamination were the dominating mechanisms at higher loads and sliding speeds. [ABSTRACT FROM AUTHOR]

High recycling rates worldwide underline the economic and environmental value of aluminum scrap. However, several alloying elements in recycled Al negatively affect the final properties of castings, among which Fe has the most permissive effect on the mechanical properties. The extremely restricted solid solubility of Fe in Al leads to the formation of brittle Fe-containing intermetallic compounds (IMCs), and a possible strategy is to use modifiers of harmful IMCs by alloying. The present work aims to investigate the substitutional characteristic of Fe, Mn, Cr in the α-IMC taking the Al-12 %Si alloy as a reference, i.e., by analyzing the directional solidification (DS) of binary (Al-12 %Si), ternary (Al-12 %Si-1 %Fe) and quaternary (Al-12 %Si-1 %Fe-1 %Mn and Al-12 %Si-1 %Fe-0.6 %Cr) alloys. For all DS alloys castings, the macrostructure is shown to be characterized by columnar grains associated with solidification cooling rates (Ṫ) from 0.4 to 42.3 °C/s. The microstructure of the four alloys examined is shown to be typified by an α-Al dendritic matrix with interdendritic regions formed by α-Al, Si and different IMCs, which have been characterized and associated with the local Ṫ. The evolvement of iron-containing IMCs morphologies according to the addition of alloying elements in Al-Si alloys, is as follows: plate-like for Fe, plate-like and Chinese script for Mn, and fishbone and trefoil/blocky for Cr. Experimental power laws equations are determined relating the primary (λ1), secondary (λ2) and tertiary dendritic arm spacings (λ3) to Ṫ, for any experimentally examined DS alloy casting. The microhardness (HV) of the alloys is correlated with λ3 and Hall-Petch type equations are derived relating HV to both λ3 and Ṫ. The Al-12 %Si-1 %Fe-0.6 %Cr alloy achieved the highest HV among all the alloys examined.

CrAlN coatings were prepared on Al–Si alloys using filter cathode vacuum arc deposition technique with nitrogen as the reactive gas and Cr 25 Al 75 alloy target as the arc source. The effect of nitrogen pressure on the microstructure, mechanical properties and electrochemical properties of the coatings had been systematically studied. The results showed that the composition, structure and performance of the CrAlN coating depended on the nitrogen pressure. As the nitrogen pressure increased, the Al and Cr content decreased while the N content increased slowly in the coating. Meanwhile, the phase structure gradually changed from AlN phase to CrN phase. The hardness of the CrAlN coating increased significantly with the increase of nitrogen pressure from 0.04 to 0.06 Pa due to the formation of CrN phase and grain refinement. However, further increasing the nitrogen pressure to 0.07 Pa, the hardness was reduced owing to the deterioration of the surface quality caused by target poisoning. Moreover, the adhesion strength of the coating gradually decreases, and the corrosion resistance of the CrAlN coating first increased and then decreased with increasing the nitrogen pressure. The CrAlN coating deposited at a nitrogen pressure of 0.05 Pa had the best corrosion resistance, with the highest polarization resistance, charge transfer resistance and pore resistance, which was related to the combined effect of great compactness and AlN-dominant phase structure in the coating. [ABSTRACT FROM AUTHOR]

A series of studies were conducted to demonstrate the feasibility of low-temperature bonding by the forming and heating an Al-8wt%Si alloy thick film on a B4C surface by cold spraying. The results show that: (1) The cracks near the joining interface are closed by the Al alloy by the process studied in this study, and a joining strength of about 220 and 240 MPa is achieved by low temperature joining of 580 °C and 600 °C, respectively.; (2) The amount of weak intermetallic compounds at the joining interface is reduced; (3) It is assumed that the reduction in the amount of Al-B-C compounds is due to the formation of the β phase during the solidification process of the Al-Si alloy, which hinders the growth of the compounds.; (4) On the primary joint surface, a continuous void group is formed in the vicinity of the β phase that surrounds the α phase, causing a decrease in the joining strength. [ABSTRACT FROM AUTHOR]

The mechanical properties of Al-Si alloys have been investigated. Abrasion wear resistance is an important analysis being used in various applications so there are many laboratory testing methods to determine it. In this article, we've looked at one of the ways to determine wear resistance using a scratch tester as a relatively easy, efficient, and fast test method. Materials used in the tests were: Al-Si (Al 94.30; Si 2.24, Fe 0.84) alloy. The coefficient of friction and wear of the samples were determined both by the methods of testing the wear and by investigating them in correlation with their mechanical properties.

Additive manufacturing of Al-Si alloy thin-walled components with/without interlayer adding La2O3 powder were obtained by cold metal transfer (CMT). Based on the optimisation of the CMT additive manufacturing process, the influences of La2O3 powder on the microstructure and properties of parts were analysed by using OM, SEM and EBSD. The results showed that by adding La2O3, the effective length and layer height of the component was increased due to the increase of the surface tension. Nucleation particles were increased by adding the La2O3, which resulted in that the α-Al and Al-Si eutectic were refined compared with that of no adding La2O3. By adding La2O3, the tensile properties of the part were improved. The refinement microstructure was the main reason for the improvement of mechanical behaviour. [ABSTRACT FROM AUTHOR]

In the laser beam powder bed fusion (PBF-LB) processes, laser parameters need to be customized for fabricating dense components. Al-Si alloys are representative Al alloys used for the PBF-LB processes. The Al-Si alloys fabricated by the PBF-LB processes exhibit characteristic microstructures and mechanical properties, which are affected by the laser parameters. This paper describes the effect of laser conditions on the relative density, microstructure, and mechanical properties of Al-12Si (mass%) alloy fabricated by the PBF-LB process. The first topic is a machine-learning-assisted exploration of laser parameters (laser power and scan speed) for fabricating dense Al-12Si alloy parts. Using a neural network model, the laser condition range for fabricating dense Al-12Si alloy parts is predicted. A methodology for accurately predicting the laser condition range for fabricating dense components is introduced. The second topic is controlling the microstructures and mechanical properties of the dense Al-12Si alloys. Variations in α-Al crystal grain size/orientation, the width of primary α-Al phase, and solute Si content in α-Al matrix with laser conditions are introduced. The changes in mechanical properties with laser conditions and correlation with microstructural features are also described. [ABSTRACT FROM AUTHOR]

In this research article, the effect of the strain-induced melt activation (SIMA) process on the microstructure and mechanical properties of the Al–7Si alloy has been investigated. The morphology of α-Al grains is changed from dendritic to fine spherical and flaky type eutectic Si to a fine fibrous eutectic Si after the modified strain-induced melt activation (M-SIMA) process. The intermetallic compounds are refined and distributed uniformly throughout the matrix after the M-SIMA process. The mechanical properties have been improved due to fine spherical grain formation with refined eutectic Si. A high tensile strength (UTS: 204 MPa) with a remarkable improvement in ductility (El: 30%) is achieved after the M-SIMA process at 585°C for 30 min in comparison to the as-cast Al–7Si alloy (UTS: 117 MPa, El: 16%). [ABSTRACT FROM AUTHOR]

The effects of Fe, Cr and thermal exposure on the microstructure and mechanical properties of Al-Si alloy were investigated in this work. The results indicated that the main phases of the Al-Si-Cu-Ni-Mg-(0.6–0.9%) Fe (wt. %) alloy were α-Al, Si, Al5Cu2Mg8Si6, Al3CuNi, Al7Cu4Ni, Al2Cu, and AlFeSi at room temperature. The size of the AlSiFe phase increased with increasing the weight fraction of Fe. The shape of Fe-rich phase changed from rod-like to star-like, followed by long needle-like with Fe varying from 0.6% to 0.9%. The mechanical properties of the studied alloys at elevated temperatures increased with Fe. The ultimate tensile strength of the three alloys at 350 °C was 111.2 MPa, 124 MPa, and 128.7 MPa, respectively. In addition, the ductility and strength of the studied alloys at room temperature decreased with increasing the Fe, due to the large size of the hard and brittle Fe-rich phase strictly cleaved the aluminum matrix. After thermal exposure, the properties of the alloy at room temperature and elevated temperature decreased obviously at the beginning of 0.5~8 h, and then tend to be stabilized during thermal exposure at 350 °C for approximately 32~64 h. Fe-rich was a thermal stable phase at 350 °C.

The aim of this article was to investigate the influences of directions and magnitudes of static electrical field (E) on eutectic spacings (λ), Brinell hardness (HB) and ultimate tensile strength (σUTS), yield strength (YS) and % elongation (%El) in the Al–12.6 wt.% Si alloy. For this purpose, the Al–12.6 wt.% Si molten alloy was solidified with different directions and magnitudes of E. Directions of E were chosen to be parallel (E+) and antiparallel (E−) to the solid–liquid (S–L) growth direction, and the magnitudes of E were in the range of 14.1–17.9 kV cm–1. The E+ and E− provided an increment or decrement in the atomic mass flux of liquid Al atoms at S–L interface during the solidification. Thus, the value of λ increased as 100% and the values of HB and σUTS decreased as 6.3 and 6.2%, respectively, with increasing the E+. But the λ value decreased as 34% and the values of HB and σUTS are increased as 8.5 and 5.6%, respectively, with increasing E−. The dependence of λ, HB and σUTS on the E+ and E− was determined by regression analysis. [ABSTRACT FROM AUTHOR]

This paper presents the study of the microstructure, wear properties of spray-deposited and hot compressed Al-35Si and Al-45Si alloys. The microstructure analysis and wear mechanisms of spray formed and as cast alloys were studied by using optical and scanning electron microscope (SEM). The microstructure of the spray-formed alloys showed fine particulate of primary Si and eutectic phases distributed uniformly in the equiaxed Al- matrix. Microstructural refinement was further increased in the hot-compressed alloys. Hardness, dry friction and wear tests were performed on spray formed alloys and compared with as cast alloys. Friction coefficient (COF) and wear rate of the alloys were measured under different applied loads (10–50 N) and sliding velocities of 1 and 1.5 m/s at constant sliding distance of 5000 m. The results indicated that the hardness and wear resistance of spray formed and hot-pressed alloys were considerably high over that of the as cast alloys. The improvements in hardness and wear resistance of spray-formed alloys were mainly attributed to morphology, size and distribution of Si particles induced during spray deposition process. Analysis of worn surfaces by SEM showed dominant wear mechanism of spray-formed alloy was mainly abrasive wear and oxidation wear. [ABSTRACT FROM AUTHOR]

Al-Si based alloy matrix composites are now broadly utilized by the industrial sectors like automobile, structural, aerospace and more practical industrial applications due to its noncompetitive economy range, good mechanical properties and less density. In order to widen its applications, it is very significant to improve its mechanical and workability behavior. So, in this work, an effort has been taken to develop a ZnO microparticles (3, 4.5 & 6 %) reinforced with Al-Si-Mg (AA6061) alloy by stir casting route.Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (X-RD) were employed for characterization studies of the composites. Tensile and hardness of the composites are investigated, compared and analyzed its effects. Another novel finding of the work is determining the workability behavior of the prepared samples with aspect ratio of 1 by incremental compressive loading of 25 kN through cold upsetting technique. For all developed samples, true axial stress (σz), hoop stress (σө), hydrostatic stress (σm), effective stress (σeff), formability stress index (β) and stress ratio parameters [(σz/σeff), (σө/σeff), (σm/σeff)] were determined and the results are correlated with the axial strain (εz). The results clearly infers that increasing weight contributions of ZnO particles increase the mechanical properties, all the stresses and stress ratio parameters of the composites. [ABSTRACT FROM AUTHOR]

The synthesis of alloys whose components show low miscibility, such as Al-Si, achieves in the mechanical alloy a method of amplifying this condition and generating microstructural changes that modify the properties of the alloy. Aluminum alloys containing 20% wt Si have been synthesized by mechanical alloying varying the grinding time and characterized by different techniques, in order to investigate the effect of grinding time on the microstructure, density and electrical resistivity. XRD measurements confirm the biphasic condition of the Al-Si system, identifying the presence of the characteristic phases Al-α and Si-δ, and detecting changes in the lattice parameters as a result of the formation of Al/Si solid solutions; A solid solution of Si in Al-α with a solubility of up to 3.14% at dissolved Si and a crystallite size of 30 nm is formed after 70 hours of grinding. The SEM-EDS study indicates a heterogeneous distribution of particles of different sizes that tend to be homogeneous for grinding times greater than 30 hours. Calorimetric studies detect a single endothermic reaction corresponding to said temperature at the beginning of fusion, in accordance with the phase diagram, and showing an increase in the enthalpy of fusion above the value of the silicon enthalpy. The density variation is directly associated with the synthesis, compaction and sintering processes. During the synthesis of the alloy, the electrical resistivity modifies its behavior from a metallic conductor to one of composite materials for long grinding times. This study corroborates the increase in the solubility of Si in Al, and its effect on the properties studied. It also reflects a gradual relaxation towards equilibrium of all the processes involved as the alloy consolidates with increasing grinding time. [ABSTRACT FROM AUTHOR]

The effects of Mg on microstructure, defects and properties of Al–Si alloy deposited by Wire and Arc-based Additive Manufacturing (WAAM) were investigated. The WAAM alloys were characterised by the metallographic microscope, X-ray diffraction, scanning electron microscope, computed tomography and electronic universal testing machine. The results show that the secondary dendrite arm spacing (SDAS) and hydrogen content of as-deposited WAAM alloy increase, and the tendency of pore formation increases with an increase in Mg content. The impurity Fe in the WAAM alloy with low Mg content is mainly in β-Fe phase, while with high Mg content is mainly in the π-Fe phase. After solution treating and ageing treatment (T6 heat-treat), the microstructure of WAAM alloy tends to be uniform. With the increase of Mg content, the size of eutectic silicon particles increases gradually. Furthermore, the UTS and YS of the alloys increased, and the elongation decreased. [ABSTRACT FROM AUTHOR]

Al-Si alloys exhibit promising wear resistance, thus being mainly employed to weld Al alloy parts and processed into components of equipment. During the new continuous casting direct rolling (CCDR) process, the raw material gradually cools and solidifies, simultaneously plastically deformed. Hence, the materials manufactured through the CCDR process presented an unparalleled microstructure. The experimental results indicated that the strength of the CCDR Al-Si alloy can be increased through cold rolling. A two-stage heat treatment (solid solution and aging treatment) was introduced to improve the ductility and satisfy the industrial application. Furthermore, the erosion wear characteristics and fracture mechanism of the CCDR Al-Si alloy dominated by the ductility were confirmed. Both cold rolling specimens (FR) and those with heat treatment (FRH) showed greater wear resistance than as-manufactured (F). The FR specimens exhibited greater wear resistance owing to a higher Al matrix strength at a lower impact angle; on the other hand, at a higher impact angle, the FRH specimens with a softer Al matrix presented better wear resistance due to the formation of a lip structure to reduce material removal. The TEM results confirmed that the nanoscale grains formation was induced in the erosion-affected region and affected the Si concentration. Conclusively, the heat-treated CCDR Al-Si alloy possessed excellent erosion resistance and workability, which can serve as a reference processed as wear-resistant mechanical parts. [ABSTRACT FROM AUTHOR]

The in situ formation of SiC in Al–40Si alloys during the fabrication of SiC/Al–Si composites by high-pressure solidification were investigated. The results demonstrate that the in situ formation of SiC occurs by a gradual conversion of Al 4 C 3 and Al 4 SiC 4 to SiC. In situ SiC can be formed in an Al–40Si alloy solidified under a pressure of 3 GPa at a temperature of 1373 K. The SiC particles (SiC p) formed in situ was compatible with the α-Al matrix and the Si phases. The relative density of the SiC/Al-38.6Si composite was 99.9%. The bending strengths of the Al–40Si alloy and the SiC/Al-38.6Si composite obtained by solidification under a pressure of 3 GPa were 200.8 MPa and 322 MPa, respectively, which represents an enhancement of 60.3% as a result of reinforcement by the in situ-formed SiC. [ABSTRACT FROM AUTHOR]

Trace elements Co, Cr were added to investigate their influence on the microstructure and physical properties of Al-Si extruded alloy. The Co, Cr elements were randomly distributed in the matrix, forms intermetallic phase and their existence were confirmed by XRD, EDS and SEM analysis. With addition of trace elements, the microstructure was modified, Si particle size was reduced and the growth rate of β-(Al5FeSi) phase limited. Compared to parent alloy, hardness and tensile strength were enhanced while the linear coefficient of thermal expansion (CTE) was significantly reduced by 42.4% and 16.05% with Co and Cr addition respectively. It is considered that the low CTE occurs with addition of Co was due to the formation of intermetallic compound having low coefficient of thermal expansion. The results suggested that Co acts as an effective element in improving the mechanical properties of Al-Si alloy.

To systematically investigate the effect of rare earth element Gd on microstructure and mechanical properties of Al-Si-Mg(A357) cast alloy, A357 alloys with different Gd additions were investigated by OM, SEM, EPMA, XRD, DSC, TEM and tensile test. The results show that the addition of Gd can refine the grain and secondary dendrite arm spacing of the alloy. Besides, Gd refines eutectic Si, instead of transforming its morphology. The mechanical properties are improved by Gd addition due to obvious refinement of the grain and eutectic Si, the reduction of secondary dendrite arm spacing. For the A357-0.5Gd(mass fraction/%) alloy, the ultimate tensile strength(UTS) is 355MPa, which is 37MPa higher than that of the alloy without Gd. However, when increasing the Gd mass fraction to 1.0%, the formation of a high number of coarse Al2Si2 Gd results in the decrease of the mechanical properties of the alloy.The refinement mechanism of Gd was investigated.Combined with the TEM observation, it can be inferred that the Gd addition produces fewer twins but some nanosized particles within eutectic Si. The density of twins is not high enough to cause the morphology transition of eutectic Si. The refinement effect of Gd on eutectic Si may be attributed to the increase of constitutional overcooling and the formation of nanosized particles, inhibiting the growth of eutectic Si during solidification.

The fatigue life of a hot extruded Al-12.7Si-0.7Mg alloy under T1, T4, and T6 conditions was studied. The microstructure and tensile properties of the alloy were investigated in order to analyze the fatigue behavior. The results of the fatigue test showed that an extruded Al-12.7Si-0.7Mg alloy provided greater fatigue life compared to a cast Al-Si alloy, which was explained by the refined microstructure characterized by fine Si particles uniformly distributed in the Al matrix of fine equiaxed grains promoted by hot extrusion. The fatigue property of the alloy in T6 treatment was higher than that in the T4 and T1 conditions due to strengthening precipitation.

The Al-Si-Cu-Mg-Ni alloy is a commonly used piston alloy. In this work, different amounts of phosphorus modifier and Al-2P (Al-2%P) master alloy modifier were added to the original alloy. The ultrasonic melt treatment method was also applied to improved the microstructure of near-eutectic multi-cast Al–Si alloys. Investigation was performed by means of optical microscopy and scanning electron microscopy. The results show that the effect of Al-2P master alloy modifier is more stable. However, the phosphorus modifier requires a higher amount of addition to achieve a refinement effect similar to that of the Al-2P modifier. The external ultrasonic field mainly acts on the AlP particle. The heterogeneous nucleation of the primary Si phase and the AlP clusters formed by the phosphorus modifier are more aggregated than the fine-dispersed AlP particles formed by the Al-2P master alloy modifier in the melt. Hence the ultrasonic melt treatment is more effective for the phosphorus modification. [ABSTRACT FROM AUTHOR]

The microstructure of samples of austenitic stainless steel and Al-Si alloy, obtained by the wire based additive method under various conditions was investigated. The effect of the beam current, the deposition intervals and the electron beam post-processing on the microstructure is shown.

The microstructure characteristics and wear behavior of a spray-deposited (SD) and the hot compressed Al-28Si alloys were investigated and the results were compared with corresponding SD and as-cast alloys. The microstructure, hardness and wear properties of the spray-deposited alloy was studied using X-ray diffraction, optical microscopy, scanning electron microscopy (SEM), microhardness measurement and wear tests. The microstructures of the SD alloy were composed of refined and uniformly distributed primary silicon (Si) and the formation a fine eutectic phase at the inter particle boundaries of an equiaxed grain morphology of the aluminum (Al) matrix. The decrease in the porosity level and further refinement of primary Si and eutectic Si phases in the hot pressed alloy. The wear tests indicate that the hot pressed spray formed alloy showed good wear resistance compared to both the SD and as-cast alloys. The improvement in the wear behavior is discussed in the light of microstructure evolution by the spray-deposition process. The worn surfaces were characterized by SEM-energy dispersive X-ray spectroscopy (EDS).

The refinement potential of Al-3.5FeNb-1.5C master alloy on pure aluminium and Al-9.8Si-3.4Cu alloy has been investigated. Different amounts of Al-3.5FeNb-1.5C master alloy were added to estimate the optimal addition level. It was found that the addition of Al-3.5FeNb-1.5C grain refi ner can promote signifi cantly the refi nement of grains in the pure aluminium, particularly at 0.1wt.%, with the mean primary aluminium α-grain size reducing to 187±3 μm from about 1-3 mm. Similarly, the microstructural study of the Al-9.8Si-3.4Cu alloy die casting at different weight percentages (viz. 0.0wt.%, 0.1wt.% and 1.0wt.%) of Al-3.5FeNb-1.5C master alloy shows that the Al-3.5FeNb-1.5C master alloy as a grain refi ner is also acceptable for Al-Si cast alloys when the silicon content is more than 4wt.%. As a result of inoculation with Al-3.5FeNb-1.5C master alloy, the average grain size of α-Al is reduced to 22±3 μm from about 71±3 μm and grain refi ning effi ciency is not characterized by any visible poisoning effect, which is the major limitation in the grain refi nement of Al-Si cast alloys by applying Al-Ti-B ternary master alloys. Mechanical properties such as ultimate tensile strength and yield strength are signifi cantly improved by 9.6% and 9.7%, respectively.

Al-18%Si-4.5%Cu alloy was processed by route BC equal-channel angular pressing (ECAP) at a temperature of 400 °C. Electron backscattered diffraction (EBSD) was used to analyze the microstructure and microtexture during the ECAP process. The microstructural results showed three important effects: First, the particle-stimulated nucleation (PSN) and continuous dynamic recrystallization (CDRX) had the main effect on the refinement of the aluminum matrix during the ECAP process. Second, after the third and fourth passes, due to redundant strain created by route BC, the heterogeneous microstructure was observed. Third, further ECAP passes led to further fragmenting and better distribution of the particles. The microtextural results showed that further ECAP passes led to strengthening the B / B ¯ component at the center and also strengthening the A*1 and A*2 components at the bottom of specimens. The microhardness results showed that the grain refinement strengthening and precipitation strengthening were the main strengthening mechanisms in the route BC-ECAPed Al-18%Si-4.5%Cu alloy. [ABSTRACT FROM AUTHOR]

The separation behaviour of primary silicon from high-silicon Al-Si melts during the directional solidification under alternating electromagnetic field with varying frequencies and pulling rates is investigated. Results show that the separation of Si from Al-Si melts significantly depends on the electromagnetic frequency and the solidification rate of the melts as well. Moreover, the separation and enrichment effects of Si electromagnetic frequency with 3 kHz was superior to 30 kHz during the electromagnetic separation process, which was independent on the initial concentration. The flat and distinct separation interfaces could be formatted by using a relatively low pulling rate of 5 μm/s and a frequency of 3 kHz. Finally, the differential scanning calorimetry analysis showed that the alloy section had good thermal stability in the whole electromagnetic separation process. This method has the prospect and potential of becoming the method for manufacturing low-cost Al-Si alloys after the electrothermal process. [ABSTRACT FROM AUTHOR]

The microstructure evolution and property change of four kinds of low silicon cast aluminum alloy exposed to heat for 0–50 h at 200°C were studied by means of Brinell hardness test, tensile property test, friction and wear property test and XRD analysis. The results show that with increasing thermal exposure time, the tensile strength of each group of samples decreased and the amount of wear increased. The tensile strength of samples with more Si content decreased slowly. When the time increased to 50 h, the increase of wear loss was the largest. The hardness of samples after thermal exposure increases compared with that before thermal exposure. The residual stress of (311) diffraction crystal surface of AlSi3.5Mg0.66 under different thermal exposure time was measured. The type of residual stress changed from residual tensile stress to residual compressive stress after thermal exposure. There is an abnormal phenomenon that the hardness of the sample increased and the amount of wear increased, and it is evident that the distribution of residual stress was inhomogeneous after thermal exposure. It is found that with increasing thermal exposure time to 50 h, the average lattice distortion ε of the low-index crystal plane and the high-index crystal plane in the aluminum alloys gradually increased. [ABSTRACT FROM AUTHOR]

This paper deals with different types of modifiers and their effect on the microstructure of the Al-Si alloy. For the purposes of this research, strontium, antimony and calcium were used as the modifiers of the AlSi10CuNiMn alloy. Unmodified alloy was cast in order to be compared with the alloy modified by different modifiers in various concentrations. The results of this research were analysed via light and electron microscopy. [ABSTRACT FROM AUTHOR]

Four-dimensional (4D) electrochemical impedance spectroscopy was applied to clarify the role of microstructures on the corrosion behaviour of Al-Si alloys additively manufactured by laser powder bed fusion in the immersion of NaCl solution. 3D complex impedance plots, comprising real, imaginary, and time axes, indicate that the impedance increases gradually at initial stage and then does not show apparent time variation. These behaviours, following surface morphology analysis, are strongly related to the remaining fine silicon particles on the surface due to the preferential Al dissolution, which suppress the further dissolution from underlying along with the protective oxide film formation. • 4-dimensional(4D) electrochemical impedance spectroscopy used for corrosion study. • Additive-manufactured Al-Si alloys with different annealing temperatures employed. • 3D complex impedance plots indicate time variation of impedance due to dissolution. • Time variation of charge transfer resistance demonstrate small dissolution rate. • Remaining fine Si particles suppress further Al dissolution with film formation. [ABSTRACT FROM AUTHOR]

Fabrication condition greatly influences the microstructures and properties of Al alloys. However, most of the available reports focus on a single fabrication technique, indicating there is still a lack of systematic comparisons among wider ranges of fabrication methods. In this paper, with conventional casting (via sand/Fe/Cu mold) and additive manufacturing (AM, via selective laser melting, SLM) methods, the effects of cooling rate (Ṫ) on the microstructures and mechanical properties of hypoeutectic Al-10Si-0.5Mg alloy are systematically investigated. The results show that with increasing cooling rate from sand-mold condition to SLM condition, the grain size (d) is continuously refined from ~3522 ± 668 μm to ~10 μm, and the grain morphology is gradually refined from coarse dendrites to a mixed grain structure composed of columnar plus fine grains (~10 μm). The eutectic Si particles are effectively refined from blocky shape under sand/Fe-mold conditions to needle-like under Cu-mold conditions, and finally to fine fibrous network under SLM condition. The tensile yield strength and elongation is greatly improved from 125 ± 5 MPa (sand-mold) to 262 ± 3 MPa (SLM) and from 0.8 ± 0.2% (sand-mold) to 4.0 ± 0.2% (SLM), respectively. The strengthening mechanism is discussed, which is mainly ascribed to the continuous refinement of grains and Si particles and an increase in super-saturation of Al matrix with increasing cooling rate.

Cooling rate plays a critical role in determining the thermal conductivity of Al-Si alloys. Although the effect of morphology and size of Si (changed by heat treatment) on its thermal conductivity has been investigated, the effect of cooling rates on thermal conductivity has not been well studied. In this study, we investigated the microstructure of an Al-8Si (with and without modification by Strontium (Sr)) alloy with cooling rates from 46.2 °C/s to 234 °C/s. It was found that the effect of cooling rate on thermal conductivity of Sr modification and Sr-free samples are opposite from each other. As a result, while the cooling rate increased from 46.2 °C/s to 234 °C/s, the calculated thermal conductivity increased from 145.3 MS/m to 151.5 MS/m for Sr-free Al-8Si alloy, and the calculated thermal conductivity was reduced from 187.5 MS/m to 176.7 MS/m for the Sr-modified Al-8Si alloy. By discussing how thermal conductivity correlates with eutectic silicon morphology and secondary dendrite arm spacing, the relationship between cooling rate and thermal conductivity were explained. This work suggests a new design strategy for improving the thermal conductivity of Al-Si hypoeutectic alloys.

This review covers research aimed at finding the optimum composition and growth rate to obtain a highly modified Al-Si alloy using directional solidification. Investigations of microstructure and mechanical properties as a function of Si content and growth rate are analyzed. These works show that the composition yielding a eutectic microstructure changes considerably with increasing solidification rate in the range of 102-104 μm/s. The increase in ultimate tensile strength with increasing Si content up to that giving a completely eutectic microstructure is explained by a redistribution of volume content of α-Al and eutectic. The increase in tensile strength with increasing rate is explained by a decrease in microstructural scale accompanying the transformation of flake-to-fiber eutectic microstructure. The optimal fine fiber structure without any primary crystals of Al-Si alloy at a given Si content is obtained at the solidification rate giving a completely eutectic microstructure at that composition. Hypereutectic alloys can be fully modified using rapid cooling at such solidification rate that causes coupled growth of the eutectic for given composition of the alloy. Additional Sr modification results in a super-modified structure, high tensile strength and record high elongation. [ABSTRACT FROM AUTHOR]

Al-Si alloy nanocomposites reinforced with nano-carbon (carbon nanotubes (CNTs), graphene nanoplatelets (GNPs)) and in-situ Al 2 O 3 were fabricated via the process of surface modification, ball milling and hot isostatic pressing (HIP). The microstructure and mechanical properties of the nanocomposites were tested and analyzed. The interface between nano-carbon and Al matrix bonded tightly for reacting at the interface to form Al 4 C 3 , and the in-situ synthesis Al 2 O 3 particles were dispersively distributed and had high bond strength with Al matrix. The nanocomposites show high compactness (≥98.5%) and excellent mechanical properties, the hardness, tensile, compressive and shear strength of the nanocomposite with 1.0 wt% CNTs are 96.4 HV, 237.7 MPa, 389.5 MPa and 130.3 MPa, respectively. The interface bonding mechanisms and strengthening mechanisms were studied in detail. The results show that the reinforcement phases mainly reinforce the nanocomposites by grain refinement strengthening, dislocations strengthening, particles strengthening and load transfer. • The Al-Si nanocomposites with isotropic microstructure and excellent mechanical properties were prepared via HIP. • The synergetic effect of nano-carbon and in-situ Al 2 O 3 in the nanocomposites were investigated. • The structure and interface of the nanocomposites were analyzed and discussed in detail. • Strengthening and fracture mechanisms of the nanocomposites were analyzed systematically. [ABSTRACT FROM AUTHOR]