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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]

The influence of ageing and ageing time on the mechanical properties, such as tensile strength and wear behaviour, of Al18Si3.6Cu0.34Ce alloy have been discussed. The As-cast alloy was subjected to T6 heat treatment (solutionization at 510° for 1 hr and ageing at-210°C) for different ageing durations like 1 hr, 3 hr, 5 hr and 7 hr, the morphology of as-cast and age hardened samples is examined by SEM and optical images, the sharp edges of primary-silicon and α-Al matrix with a columnar grain structure of untreated alloy changed after ageing, they are rounded off, spheroidisation with uniform redistribution of Al2Cu blocks, Al2CeSi intermetallic precipitates are formed with improved grain boundaries, and it develops obstacles in larger scale to the flow of dislocation mechanism, so it strengthens the metal matrix. Compared to as-cast alloy, the mechanical properties are improved after ageing. For 5-hr aged samples, the yield strength (YS) elevated to 127.44 MPa (improved by 83%) with an elongation rate of 1.64% (41.4%) as compared to as-cast alloy, and the ultimate tensile strength of as-cast alloy (158.2 MPa) enhanced to 193.835 MPa and 168.7 MPa after 1 hr and 3 hr ageing, respectively. Ageing improves the flow stress, which is predominantly the effect of homogenisation. Considerable improvements in the wear resistance after age hardening were noticed; both VWR and COF both a linear relation, with applied load at constant speed. As-cast and 7-hr aged samples show poor wear resistance due to co-existence of incoherent phases (Al2Cu and Si) in the metal matrix, and alloy ageing for 1 hr, 3 hr and 5 hr improves the load bearing and shear strength. [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]

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 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]

Two types of microcapsules, namely, Al-10Si@Al 2 O 3 and Al-12Si@Al 2 O 3 , were prepared by pressure steam corrosion combined with heat treatment. The alloy raw materials of Al-10Si and Al-12Si, microcapsule precursors Al-10Si@AlOOH and Al-12Si@AlOOH, and microcapsules Al-10Si@Al 2 O 3 and Al-12Si@Al 2 O 3 were characterized by X-ray powder diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The latent heat and microstructures of the two microcapsules following thermal cycles in an air atmosphere were investigated. The physical models of the microcapsules with and without primary Si precipitation were established, and their thermal-stress distributions were numerically simulated. Results showed that the latent heat of the two microcapsules decreased with an increase in the number of thermal cycles. The cyclic thermal performance degradation mechanism of Al-10Si@Al 2 O 3 and Al-12Si@Al 2 O 3 was as follows: Al consumption formed the shell layer and Al oxidation moved the alloy composition points toward the 100 wt %Si point on the Al-Si binary phase diagram. The precipitation of primary Si led to shell fragmentation due to alternating stress, and the exposed Al was further oxidized, thus reducing the cyclic heat storage performance of the microcapsules. This study provides guidelines for maintaining the latent heat stability of Al-Si alloy microcapsules following thermal cycling in an air atmosphere. [Display omitted] • Al-10Si@Al 2 O 3 and Al-12Si@Al 2 O 3 microcapsules were prepared and their latent heats and microstructures were investigated. • The primary silicon is gradually precipitated at the interface of core and shell during the thermal cycles. • Thermal stress distribution of microcapsules with and without primary silicon precipitation were numerical simulated. • The degradation mechanism of latent heat of microcapsules during thermal cycles were discussed. [ABSTRACT FROM AUTHOR]

The corrosion mechanism evolution of four low silicon-cast aluminium alloys exposed to heat treatment at 200°C for 0–50 h was studied by means of immersion corrosion, intergranular corrosion and electrochemical test, SEM, EDS and EBSD analysis methods. The correlation of corrosion resistance with composition and the thermal exposure time was investigated. The results show that the corrosion mechanism of all aluminium alloys changed after thermal exposure at 200°C. Before thermal exposure, intergranular corrosion was the main corrosion, and after 200°C thermal exposure, serious pitting corrosion and spalling corrosion occurred in the local area. The contents of Si and Mg in the grain boundary increased obviously. The contents of elements in the poor zone of the grain boundary increased, and the electrical potential difference between the grain and the grain boundary reduced. The intergranular corrosion sensitivity of the alloy was reduced. But the degree of pitting gradually becomes serious. The electrochemical test of the aluminium alloy with 3.5 wt% Si showed that its corrosion potential increased with the increase inthermal exposure time, and its corrosion current density increased with the increase inthermal exposure time. After the EBSD test, it was found that the large angle grain boundary decreased gradually and the proportion of large grain size increased with the increase in thermal exposure time to 50 h. [ABSTRACT FROM AUTHOR]

Improving the engineering properties of Al–7Si cast alloys (300 series) provides an attractive alternative to automotive and aircraft engine industries. The solubility limit of silicon (Si) in Al contributes to the precipitation of flake-shaped Si particles with sharp edges, which function as a stress riser and promote crack propagation during the eutectic phase while also weakening the protective layer's durability. In this study, the impact of microstructure refinement of Al–7Si alloys by using cooling slope, thixoforming and the T6 heat treatment process on hardness and corrosion resistance behavior was investigated. Results showed that the microstructures of the as-cast alloy had a very coarse dendritic shape, whereas the dendritic transferred to the globular α-Al phase, and the Si particles were replaced into a lamellar- or acicular-like shape after the cooling slope and thixoforming process, respectively. The as-cast, cooling slope and thixoformed samples were subjected to the T6 heat treatment process, which enhanced the hardness to 79, 99 and 104 HV, respectively, due to Si particle refinement. The potentiodynamic test revealed that the corrosion rate dropped to 0.00790 and 0.00736 mmpy−1 in the heat-treated cooling slope and thixoforming samples. This finding can be attributed to the substantially refined Si particles and reduced eutectic phase area due to the smaller cathodic to anodic area ratio. [ABSTRACT FROM AUTHOR]

AlSi12(Fe), AlSi10Mg(Fe), AlSi10MnMg, and AlMg4Fe2 die-casting alloys were produced by high-pressure die casting (HPDC) and vacuum-assisted high-pressure die casting (VADC) under a vacuum level of 200 mbar. The chemical composition, hardness, gas and shrinkage porosity, and mechanical properties were analyzed. The parts under study were subjected to a T6 heat treatment. The VADC led to a decrease in the percentage of defects in the as-cast state for all the alloys, due to a reduction in the amount of gas porosities. After heat treatment, the quantity of gas and shrinkage porosities increased. The efficiency and level of vacuum used were not sufficient to improve the mechanical properties in the as-cast state. The ductility of AlSi10Mg(Fe) and AlSi10MnMg alloys was improved after heat treatment; however, the YS and UTS of AlSi10Mg(Fe) did not increase. The primary aluminum alloys presented higher elongation values than the secondary aluminum alloys due to the reduced amount of the needle-like β-Al5FeSi phase. [ABSTRACT FROM AUTHOR]

Aluminum high pressure die casting (HPDC) technology has evolved in the past decades, enabling stronger and larger one-piece casting with significant part consolidation. It also offers a higher design freedom for more mass-efficient thin-walled body structures. For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting (for instance, shock towers and hinge pillars, etc.), a costly T7 heat treatment comprising a solution heat treatment at elevated temperatures (450 °C-500 °C) followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement. To enable cost-efficient mass production of HPDC body structures, it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties. Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components. The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy (registered as A379 with The Aluminum Association, USA) to achieve the desired tensile properties without using T7 heat treatment. It was found that Cu addition should be avoided, as it is not effective in enhancing strength while degrades tensile ductility. Mg addition is very effective in improving strength and has minor impact on tensile ductility. The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars. [ABSTRACT FROM AUTHOR]

The aim of this study is to identify the deformation behavior of a high-pressure die-cast Silafont®-36 aluminum alloy in an overaged T7 condition in relation to the significant microstructural changes caused by the overaging heat treatment. The T7 aluminum alloy exhibited a distinctive composite-like microstructure, consisting of coarser α-Al grains and larger spherical Si particles embedded in the matrix, in contrast to its as-cast and T4 counterparts. The softer α-Al matrix of the T7 alloy as revealed by the nanohardness and microhardness led to improved ductility and longer strain-controlled fatigue life at higher strain amplitudes, despite the lower strength. Cyclic stabilization was observed to be a salient feature of the T7 alloy, stemming from the equilibrium between cyclic hardening and cyclic softening. Strain-energy density-based model, by incorporating a material parameter called 'intrinsic fatigue toughness', could be used to predict the fatigue life of the alloy. [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]

This study fabricated a thixoformed Al-7% Si alloy using the cooling slope technique and subjected it to heat treatment before processing with severe plastic deformation to determine the effect of this combination method on the microstructure refinement and hardness of Al-Si alloys (300 Series). Each as-cast and thixoformed Al-Si alloy sample was subjected to equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) individually at room temperature before and after heat treatment. ECAP was conducted in a mould with a 120° channel angle via route A, and HPT was applied with 0.75 and 5 turns. The heat-treated thixoformed Al-Si alloy subjected to the HPT process had an ultra-fine grain microstructure and showed a fine and homogeneous redistribution of the eutectic phase in the Al matrix. For the as-cast alloy, the hardness of the heat-treated thixoformed Al-7% Si alloy increased from 63 HV to 124 and 215 Hv after two ECAP passes and five turns of HPT due to the reduced and redistributed eutectic phase in the Al matrix. Subjecting the Al-7% Si alloy to a combination of semisolid and heat treatment processes before subjecting it to severe plastic deformation resulted in microstructural refinement and improved the hardness of the Al-Si alloy. The results indicate that HPT is a more effective method than ECAP for increasing the hardness of the thixoformed Al-Si alloy due to microstructure refinement.

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 age hardening effect in Fe, Ni and Cr added hyper-eutectic Al-Si automotive alloy has been studied to isochronal and isothermal ageing at various temperatures for different times. It is observed that double aging peaks takes place in the aged alloys due to the formation of GP zones and metastable phases. Fe addition improves the hardness but decreases the tensile properties due to presents of Fe rich intermetallic especially for needle-like β-Al5FeSi. Addition of Ni does not show the positive effect in strength of the experimental alloys. Cr recovers the strength because of the modification of the morphology and the type of Fe-rich intermetallic phases in the cast alloys. It is seen from the microstructure that the needle-like β-Al5FeSi have been refined significantly due to addition of Cr. SEM fractographs show the crack initiation for Fe added alloys by massive cleavage of the brittle β-Al5FeSi phase [ABSTRACT FROM AUTHOR]

The paper presents results of a study concerning an AlSi7Mg alloy and the effect of subjecting the liquid metal to four different processes: conventional refining with hexachloroethane; the same refining followed by modification with titanium, boron, and sodium; refining by purging with argon carried out in parallel with modification with titanium and boron salts and strontium; and parallel refining with argon and modification with titanium, boron, and sodium salts. The effect of these four processes on compactness of the material, parameters of microstructure, and fatigue strength of AlSi7Mg alloy after heat treatment. It has been found that the highest compactness (the lowest porosity ratio value) and the most favorable values of the examined parameters of microstructure were demonstrated by the alloy obtained with the use of the process including parallel purging with argon and modification with salts of titanium, boron, and sodium. It has been found that in the fatigue cracking process observed in all the four variants of the liquid metal treatment, the crucial role in initiation of fatigue cracks was played by porosity. Application of the process consisting in refining by purging with argon parallel to modification with Ti, B, and Na salts allowed to refine the microstructure and reduce significantly porosity of the alloy extending thus the time of initiation and propagation of fatigue cracks. The ultimate effect consisted in a distinct increase of the fatigue limit value. [ABSTRACT FROM AUTHOR]

Chromium (Cr) is rarely added to Al–Si die cast alloys as it has a strong tendency to induce the formation of coarse-sized sludge particles. In the present study, high pressure die-cast samples made of Al-7wt.%Si–Cr–Mg alloys with varied Fe contents (0.11 wt%, 0.26 wt% and 0.32 wt%) were tensile tested under as-cast and T5 heat-treated conditions, in comparison to those made of Al-7wt.% Si–Mn–Mg alloy with a constant Fe content (0.11 wt%). The results demonstrated that under the as-cast condition, the Al–Si–Cr alloys with higher Fe contents can achieve comparable tensile properties as the Al–Si–Mn alloy with strictly controlled Fe level. However, after a T5 heat treatment (205 °C for 60 min), the increment in yield strength is less for the Al–Si–Cr alloys in relative to the Al–Si–Mn alloy, regardless of Fe contents. Scanning electron and scanning transmission electron microscopic characterizations were conducted on the as-cast and heat-treated microstructures, aiming to understand the undermined ageing response caused by Cr addition. • Ageing-induced increment in tensile yield strength is less for Al–Si–Cr–Mg alloys in comparison to Al–Si–Mn–Mg alloy. • Ageing-induced increment in tensile yield strength is mainly determined by the precipitation behavior at sub-surface location. • The intervention of Cr solute atoms on nucleation process of Si nanoprecipitate at sub-surface location undermined ageing response of Al–Si–Cr–Mg alloys. [ABSTRACT FROM AUTHOR]

Issues connected with high quality casting alloys are important for responsible construction elements working in hard conditions. Traditionally, the quality of aluminium casting alloy refers to such microstructure properties as the presence of inclusions and intermetallic phases or porosity. At present, in most cases, Quality index refers to the level of mechanical properties – especially strength parameters, e.g.: UTS, YS, HB, E (Young’s Modulus), K1c (stress intensity factor). Quality indexes are often presented as a function of density. However, generally it is known, that operating durability of construction elements depends both on the strength and plastic of the material. Therefore, for several years now, in specialist literature, the concept of quality index (QI) was present, combines these two important qualities of construction material. The work presents the results of QI research for casting hypoeutectic silumin type EN AC-42100 (EN AC-AlSi7Mg0.3), depending on different variants of heat treatment, including jet cooling during solution treatment.

In this paper, the effects of size, morphology and distribution of eutectic silicon on the thermal conductivity of Al-8Si alloy modified by Sr (0.04, 0.08, 0.12 wt.%) and Sb (0.1, 0.3, 0.5 wt.%) elements with T6 heat treatment were investigated. The results show that the modified fibrous eutectic silicon has a significant capability of improvement of thermal conductivity, while the amount of the modifier has a relatively weak effect on thermal conductivity. After T6 treatment, the fracture or spheroidization of the flake eutectic silicon and the disappearance of clustering phenomenon could raise thermal conductivity, but the coarsening of fibrous eutectic silicon is inconducive to thermal conductivity. Finally, the effect of eutectic silicon on electron transport is analyzed in detail, which could provide a reference for enhancing the thermal (or electrical) conductivity of hypoeutectic Al-Si alloy through effective microstructure control.

Recently, the materials industry has become more interested in the production of aluminum alloys due to their good properties. This paper reports on studies of the influences of the heat treatment on the microstructure and the mechanical properties of welded joints of an aluminum alloy Al - 12 mass % Si according to the standard (DIN EN231). Electric arc is the welding technique used. The microstructures of the welded joints were analyzed using a scanning electronic microscope and an X-ray diffractometer. Mechanical properties were studied by microhardness. The results obtained make it possible to show the importance of the heat treatment application in order to reduce the welding effect on the aluminum alloy, the optimal temperature to obtain a homogeneity hardness values for heat affected zone and the fusion zone is between 400°C and 500°C. The presence of a protective layer of aluminum oxide at FZ and HAZ can protect them from corrosion. [ABSTRACT FROM AUTHOR]

An intensive formation of crystal defects in the α-Al matrix of an as-cast Sr-modified eutectic Al–Si alloy, induced by heat treatment with rapid heating, has been studied. This phenomenon arises from the fragmentation of the Si crystals and the diffusion of Al atoms into the cracks of the Si crystals. During the rapid heating process, a large temperature gradient is established within an as-cast Al–Si sample. It creates a tensile environment for the irregular-shaped and interconnected Si crystals, as the thermal expansion coefficient of the α-Al is ten times that of the Si. Under the thermal constraints, some Si crystals are broken, where the cracks produce the so-called “capillary force” that attracts the surrounding α-Al matrix to fill in them. As the migration of the Al atoms is substitutional, the Al diffusion creates fluxes of vacancies to the interior of the αAl matrix; thus, the crack volume is transferred to the αAl matrix. Due to the homogeneous distribution of the Si crystals and the random presence of the cracks, the αAl matrix is subjected to a varied migration of vacancies in site, in quantity and in direction. Such diffusion is further perturbed by local migration of Al atoms to accommodate the spheroidization of the Si induced by its shape instability. In this way, a large amount of crystal defects (vacancies and then dislocations) are produced in the α-Al matrix. The produced crystal defects then promote the recovery and even recrystallization of the α-Al matrix, resulting in its refinement. Such a mechanism of defect production is applicable to polycrystalline materials composed of phases with incompatible thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

In this work, the effects of Cr content (0–0.67 wt%) and heat treatment on the microstructure evolution and high temperature (HT) tensile strength (350 °C) of the Fe-containing eutectic Al–Si alloy were studied. The results show the main intermetallics are similar in tested specimens at both different heat treatment states, including γ-Al 3 CuNi, δ-Al 7 Cu 4 Ni, Al 4 Cu 2 Mg 8 Si 7 , and AlFeSi. The addition of Cr leads to the transformation from needle-like β-AlFeSi phases to fishbone-like α-Al(Fe,Cr)Si phases. For the HT strengths (350 °C), the UTSs of Al–Si alloys at T5 state are higher than T6 state correspondingly, both of which are progressively decreased with the Cr contents. For the elongation, the Al–Si alloys at T6 state have better plasticity than T5 state correspondingly. Comparably, the elongations remain stable at T5 state, and keep increasing at T6 state with the addition of Cr. The variations of HT strengths and elongations dependent on the Cr content and heat treatment are accounted on the microstructural evolutions, including AlFeSi phase transformation and the Si spheroidization. [ABSTRACT FROM AUTHOR]

The stress states in Si particles of cast Al–Si based alloys depend on its morphology and the heat treatment given to the alloy. The Si particles fracture less on modification and fracture more in the heat treated condition. An attempt has been made in this work to study the effect of heat treatment and Si modification on the stress states of the particles. Such understanding will be valuable for predicting the ductility of the alloy. The stress states of Si particles are estimated by Raman technique and compared with the microstructure-based FEM simulations. Combination of Electron Back-Scattered Diffraction (EBSD) and frequency shift, polarized micro-Raman technique is applied to determine the stress states in Si particles with (1 1 1) orientations. Stress states are measured in the as-received state and under uniaxial compression. The residual stress, the stress in the elastic–plastic regime and the stress which causes fracture of the particles is estimated by Raman technique. FEM study demonstrates that the stress distribution is uniform in modified Si, whereas the unmodified Si shows higher and more complex stress states. The onset of plastic flow is observed at sharp corners of the particles and is followed by localization of strain between particles. Clustering of particles generates more inhomogeneous plastic strain in the matrix. Particle stress estimated by Raman technique is in agreement with FEM calculations. [ABSTRACT FROM AUTHOR]

Layered composite structures can be generated in metallic sheets by roll bonding of dissimilar metals/alloys. In this investigation, heat treatable (Al(Cu)) and non-heat treatable (Al(Si)) aluminium alloys are roll bonded in sheet form. Large hardness differences between layers poses significant bonding challenges in the form of multiple necking within the hard Al(Cu) layers. For successful processing, it is vital to choose the candidate materials in a state of marginal hardness differences during rolling, but being capable of altering properties through subsequent heat treatments. Atomic diffusion takes place during heat treatment of the composite sheet and results in gradual hardness variation across sheet thickness. The Al(Cu) layers contribute to strength, whereas the Al(Si) layers provide protection from corrosion/wear-related degradation in the newly developed hybrid sheet. The overall mechanical properties of the heat-treated composite fall between the base alloys. The bonding interfaces are noted as the potential spots for initiating failure. [ABSTRACT FROM PUBLISHER]

A 2D multi-particle model is carried out to understand the effect of microstructural variations and loading conditions on the stress evolution in Al-Si alloy under compression. A total of six parameters are varied to create 26 idealized microstructures: particle size, shape, orientation, matrix temper, strain rate, and temperature. The effect of these parameters is investigated to understand the fracture of Si particles and the yielding of Al matrix. The Si particles are modeled as a linear elastic solid and the Al matrix is modeled as an elasto-plastic solid. The results of the study demonstrate that the increase in particle size decreases the yield strength of the alloy. The particles with high aspect ratio and oriented at 0° and 90° to the loading axis show higher stress values. This implies that the particle shape and orientation are dominant factors in controlling particle fracture. The heat treatment of the alloy is found to increase the stress levels of both particles and matrix. Stress calculations also show that higher particle fracture and matrix yielding is expected at higher strain rate deformation. Particle fracture decreases with increase in temperature and the Al matrix plays an important role in controlling the properties of the alloy at higher temperatures. Further, this strain rate and temperature dependence is more pronounced in the heat-treated microstructure. These predictions are consistent with the experimentally observed Si particle fracture in real microstructure. [ABSTRACT FROM AUTHOR]

Excellent thermal conductivity and lower density make Al-Si alloys a suitable alternative for cast iron in the fabrication of engine components. The increase in the maximum operation temperature and pressure of engines necessitates improving the thermomechanical fatigue performance of Al-Si alloys. This paper has two major parts focussing on the use of Al-Si based alloys in cylinder heads and engine blocks. In the first part, the structural stress-strain and material property requirements of cylinder heads are discussed. In addition, the physical and mechanical properties of different competing materials used in the manufacture of engine components are reviewed. The physical metallurgy, solidification sequence and thermal conductivity of Al-Si based alloys are reviewed. Also discussed is the effect of microstructural features on thermomechanical fatigue lifetime. This part also includes an overview of the strengthening mechanisms of cast Al-Si alloys, by dispersed phases and heat treatment. Demands to improve fuel economy and reduce emissions necessitate modifications in the materials and design of engine blocks. Wear resistance and low friction coefficient are the major characteristics required for engine block materials. In the second part, the most promising alternative approaches to manufacturing liner-less Al-Si alloy cylinder blocks are elaborated. [ABSTRACT FROM AUTHOR]

Laser surface remelting (LSR) has shown great application potential in Al-Si alloy parts (e.g., surface strengthening, surface repairing). However, the microstructural details and properties of LSR-treated hypoeutectic Al-Si alloy remains to be investigated. In this work, the microstructure of an Al-7Si alloy with adding 0.05 wt% Ce fabricated by LSR was studied through multi-scale characterization. Three regions with distinct morphologies after LSR were obtained: i) the remelting zone (RMZ) including an equiaxed grain region and a columnar to equiaxed transition (CET) region; ii) the heat-affected zone (HAZ) with segregation of Si; iii) substrate zone (SZ). Nanoscale eutectic Si particles were observed in RMZ and HAZ. Moreover, it is confirmed for the first time that the Ce atom can absorb on the {111} Si planes and leads to high density of twins and stacking faults. After LSR, the increased microhardness of RMZ is mainly attributed to the precipitation and dislocation strengthening. By further T6 heat treatment, the microhardness of RMZ increases to 126 HV. Dispersed small Si particles decrease the critical stress of crack propagation. Additionally, the high density of twins, stacking faults and Al-rich clusters within Si particle plays a significant role in toughness improvement. • LSR-treated A356 alloy shows a developed dendrites microstructure with high density of dislocations and Si clusters. • The absorption of Ce atom columns on the {111} Si leading to the formation of twins/stacking faults is firstly observed. • Dislocation and precipitation are dominant strengthening mechanisms, and microhardness reaches 126 HV after T6 treatment. • High density of twins/stacking faults and Al-rich clusters in eutectic Si is beneficial for improving toughness. [ABSTRACT FROM AUTHOR]

This article discusses some observations pertaining to the abrasive wear response of an Al-Si alloy as influenced by microstructural features and test parameters (applied load and traversal distance). The wear performance has also been correlated with corresponding changes in mechanical properties (hardness, UTS, and elongation) and morphology (length, diameter, and length/diameter ratio) of microconstituents like Si. Microstructural/morphological alterations in the alloy were brought about through T6 heat treatment involving solutionizing followed by artificial aging for different durations. Heat treatment brought about significant alterations in the morphology (length, diameter, and length/diameter ratio) of Si particles, as was also reflected in terms of microstructural changes. The length of the Si particles decreased while their diameter increased leading to a reduction in the aspect (length/diameter) ratio of the phase in the case of the heat-treated samples compared to the as cast alloy. Decreasing length, rising diameter, and reduction in the aspect (length/diameter) ratio indicates a higher degree of spheroidization of the phase as a result of heat treatment. Increasing aging duration caused the aspect ratio to decrease further. The study suggests increasing wear loss with a rise in the applied load and traversal distance. The heat-treated samples attained improved mechanical and reduced wear loss over the as-cast samples in general, an exception being the elongation wherein the property became comparable to that of the as-cast alloy at aging durations beyond 7 h. Also, aging for 3 h seems to be sufficient to realize the benefit of heat treatment in terms of improvement in the wear behavior and mechanical properties since it leads to the highest hardness, UTS and elongation properties. Aging durations longer than 3 h led to deterioration in the UTS and elongation properties, while hardness and wear loss attained steady-state condition. The wear-related observations have further been substantiated through the characteristics of wear surfaces, subsurface regions and abrasive medium. The operating material removal mechanisms were observed to be capping, clogging, attrition, and fragmentation of the abrasive medium (particles). An interesting inference of the present study is that there seems to be a direct correlation between abrasive wear response and hardness of the alloy, while properties like UTS and elongation produce a mixed influence. [ABSTRACT FROM AUTHOR]

Abstract: Evolution of tribological properties of electroless Ni–P and Ni–P–Al2O3 coating on an Al–10Si–0.3Mg casting alloy during heat treatment is investigated in this work. The pre-treated substrate was plated using a bath containing nickel hypophosphite, nickel lactate and lactic acid. For preparation of fiber-reinforced coating Al2O3 Saffil fibers pre-treated in demineralised water were used. The coated samples were heat treated at 400–550°C/1–8h. Tribological properties were studied using the pin-on-disc method. It is found that the best coating performance is obtained using optimal heat treatment regime (400°C/1h). Annealing at higher temperatures (450°C and above) leads to the formation of intermetallic compounds that reduce the coating wear resistance. The reason is that the intermetallic phases adversely affect the coating adherence to the substrate. The analysis of wear tracks proves that abrasion is major wear mechanism, however due to the formed intermetallic sub-layers, partial coating delamination may occur during the pin-on-disc test on the samples annealed at 450°C and above. It was found that fiber reinforcement reduces this scaling and increases wear resistance of coatings as compared to the non-reinforced Ni–P coatings. [Copyright &y& Elsevier]

In the present work, electroless Ni-P-Al2O3 and Ni-P-SiC composite coatings on an aluminium-silicon casting alloy are studied. A suspension containing nickel lactate, nickel hypophosphite, lactic acid, water, and dispersed ceramic particles was used for the electroless deposition. The structural study, hardness, and abrasion tests reveal that properties of the coatings strongly depend on the composition of deposition bath and on the heat treatment. The composite coatings heat treated at 400°C/1 h showing outstanding abrasion resistance are promising candidates for surface protection of light components. [ABSTRACT FROM AUTHOR]

Selective Laser Melting (SLM) is an innovative additive manufacturing technology that facilitates the design and manufacture of complex lightweight parts with improved mechanical properties. The current study investigates the impact of post-processing such as heat treatment and Electric Discharge Alloying (EDA) on the lubricated tribological behaviour of SLM Al–Si alloy at ambient and elevated temperatures in comparison with the tribological behaviour of conventionally cast Al–Si alloy. The lubricated sliding wear experiment conducted using a Pin on Disk (POD) tribometer with EN-31 alloyed steel as a counter body. The EDA treatment is highly appealing and enhanced the wear resistance of SLM Al–Si alloy by 14.07% and 24.07% at ambient and elevated temperatures, respectively. Moreover, the EDA treatment increased the wear resistance of cast Al–Si alloy by 28.82% and 46.28% at ambient and high temperatures, respectively, due to the development of a wear-resistant carbide (SiC) and oxide (Al 2 O 3) rich modified layer on the surface. The T6 heat treatment in SLM Al–Si alloy caused deterioration in wear resistance by 10.74% and 36.73% at ambient and elevated temperature, respectively, due to the coarsening of the finer microstructure formed during SLM. In contrast, the T6 heat treatment in cast Al–Si alloy is highly effective in terms of wear resistance with an improvement of 13.26% and 13.64% at ambient and elevated temperature, respectively, due to the hardening effect caused by heat treatment. The prominent wear mechanism identified for all samples at both experimental conditions is severe abrasive wear due to plastic deformation. • Impact of heat treatment & Electric Discharge Alloying on lubricated tribological behaviour of SLM Al–Si alloy is presented. • Electric Discharge Alloying treatment improved hardness and wear resistance of SLM Al–Si alloy. • Heat treatment reduced hardness and wear resistance of SLM Al–Si alloy. • Elevated temperature wear test triggered deterioration of lubricant property and wear resistance. [ABSTRACT FROM AUTHOR]

Abstract: The work is concerned with the high-temperature heat treatment of an Al–12wt.% Si alloy coated by an electroless Ni–P layer. The electroless deposition took place on a pre-treated substrate in a bath containing nickel hypophosphite, nickel lactate and lactic acid. Resulting Ni–P deposit showed a thickness of about 8μm. The coated samples were heat-treated at 200–550°C/1–24h. LM, SEM, EDS and XRD were used to investigate phase transformations. Adherence to the substrate was estimated from the scratch test and microhardness of the heat-treated layers was also measured. It is found that various phase transformations occur, as both temperature and annealing time increase. These include (1) amorphous Ni–P→Ni+Ni3P, (2) Al+Ni→Al3Ni, (3) Ni3P→Ni12P5 +Ni, (4) Ni12P5 →Ni2P+Ni, and (5) Al3Ni+Ni→Al3Ni2. The formation of intermetallic phases, particularly Al3Ni2, leads to significant surface hardening, however, too thick layers of intermetallics reduce the adherence to the substrate. Based on the growth kinetics of the intermetallic phases, diffusion coefficients of Ni in Al3Ni and Al3Ni2 at 450–550°C are estimated as follows: D(Al3Ni, 450°C)≈6×10−12 cm2 s−1, D(Al3Ni, 550°C)≈4×10−11 cm2 s−1, D(Al3Ni2, 450°C)≈1×10−12 cm2 s−1 and D(Al3Ni2, 550°C)≈1×10−11 cm2 s−1. Mechanisms of phase transformations are discussed in relation to the elemental diffusion. [Copyright &y& Elsevier]

Abstract: This paper presents results of structural, mechanical and tribological tests of thixocast hypoeutectic Al–Si alloy A356 (EN AlSi7Mg0.3). The pin-on-disc tribometer was used to carry out tribological tests under dry sliding conditions at different loads. Two sets of specimens were used as pin materials. The first one was taken from the original alloy billet and the second one from thixocast alloy. Heat treatment was applied on both sets of specimens. The results showed that, for all applied loads, heat treatment improved tribological properties, while improvements caused by additional thixocasting were not systematic, i.e. lower friction coefficient was noticed just for lower specific loads. Overall better wear resistance of thixocast materials, compared to the originally alloy, was attributed mainly to their higher silicon content. [Copyright &y& Elsevier]

In the present study, an attempt is made to synthesize Al–Si alloy–SiC particle reinforced composite using liquid metallurgy route and to characterize the composites in terms of microstructure, mechanical properties, and sliding wear behaviour. The composite shows uniform distribution of SiC particles and good interface bonding between SiC particles and the metallic matrix. The sliding wear behaviour is studied using pin-on-disc apparatus against EN32 steel disc at different applied loads and constant sliding speed. The results show that the composite exhibits higher wear resistance, higher seizure pressure, less frictional heating, greater seizure temperature, and marginally lower coefficient of friction when compared with the alloy irrespective of applied load and sliding speed. [ABSTRACT FROM AUTHOR]

Constantly growing requirements concerning the quality of poured machinery components give rise to the need to find new solutions to improve their mechanical and technological properties, considering economic and ecological aspects resulting from energy consumption of the casting and heat treatment processes. This study presents the investigation of the effect of heat treatment on mechanical properties (tensile strength Rm, elongation A5, hardness HBW) of the AlSi7Mg alloy without modification and modified with strontium. Obtained results allowed us to determine T6 heat treatment parameters associated with the improvement of mechanical properties of the alloy with simultaneous limitation of duration of solutioning and aging treatments. The maximum increase in Rm was 67%, and 55% in the case of HBW, with a slight decrease in elongation (approx. 10%) in relation to an alloy not subjected to heat treatment in the adopted scope of tests for the total time of heat treatment of 4–6 h. The increase in elongation of up to 250% requires aging at a temperature exceeding 300 °C, which also causes a decrease in durability and hardness by 20%. Modification of the alloy using strontium before heat treatment facilitates the process of fragmentation and balling of silicone precipitates. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study investigated the active strengthening precipitates existing in the structure of 354-type Al–Si–Cu–Mg cast alloys following the addition of Zr as a primary alloying element in addition to Ni and Mn in different amounts and combinations. The investigation comprised three main parts: the first part simulated the formation and dissolution of strengthening precipitates and their precursors using differential scanning calorimetric (DSC) heating analysis of as-quenched samples, the second part presented transmission electron microscopy (TEM) observations of the fine precipitates existing in the structure of the alloys studied, and the third part examined the mechanical performance (tensile properties and hardness values) of the alloys studied. Interpretation of the DSC heating data in accordance to the available literature showed that the alloys are strengthened primarily by θ-Al2Cu and S–Al2CuMg precipitates and their precursors. Furthermore, some of the copper content was consumed in forming Al–Ni–Cu particles instead of the θ-Al2Cu strengthening phase and its precursors and hence the Ni-free alloys contain higher fractions of the θ-Al2Cu phase and its precursors than the Ni-containing alloys. TEM investigations confirmed the results obtained from the DSC heating analysis regarding the combined strengthening effect of θ-Al 2 Cu and S –Al 2 CuMg precipitates and their precursors as well as the fraction of θ-Al 2 Cu phase in Ni-free and Ni-containing alloys. TEM observations revealed, also, that the alloys studied have a secondary strengthening effect which is exerted by precipitates in the form of Al x (Zr,Ti)Si that formed following the addition of Zr. The Mechanical performance showed to be highly dependent on the chemical composition which controls alloys structure and response to the applied heat treatment and hence the formation of the fine precipitates which are mainly responsible to the strengthening effect. [ABSTRACT FROM AUTHOR]

The paper presents the results of study concerning the evaluation of the precipitation hardening parameters (temperatures and times of solution treatment and artificial ageing processes) having an effect on mechanical properties, and the change in the microstructure of the EN AC-AlSi11(Fe) alloy. Based on the obtained results and performed statistical analysis, regression equations and the response surface model in the form of spatial and contour plots were determined to illustrate the effects of solution treatment and artificial ageing parameters on the mechanical properties of the investigated alloy. The performed heat treatment had a positive effect on improving the mechanical properties of the alloy versus the initial state. The maximum increase in tensile strength was by 52%, in unit elongation by 56%, in Brinell hardness by 44% and impact strength by 88%. Furthermore, a favorable change was observed in the microstructure of the investigated alloy, especially regarding eutectic silicon precipitations, which underwent partial spheroidization and coagulation after the heat treatment. [ABSTRACT FROM AUTHOR]

In this paper, the effects of size, morphology and distribution of eutectic silicon on the thermal conductivity of Al-8Si alloy modified by Sr (0.04, 0.08, 0.12 wt.%) and Sb (0.1, 0.3, 0.5 wt.%) elements with T6 heat treatment were investigated. The results show that the modified fibrous eutectic silicon has a significant capability of improvement of thermal conductivity, while the amount of the modifier has a relatively weak effect on thermal conductivity. After T6 treatment, the fracture or spheroidization of the flake eutectic silicon and the disappearance of clustering phenomenon could raise thermal conductivity, but the coarsening of fibrous eutectic silicon is inconducive to thermal conductivity. Finally, the effect of eutectic silicon on electron transport is analyzed in detail, which could provide a reference for enhancing the thermal (or electrical) conductivity of hypoeutectic Al-Si alloy through effective microstructure control. [ABSTRACT FROM AUTHOR]

Al-20Si alloy with high thermal conductivity and adequately low coefficient of thermal expansion is successfully produced by hot extrusion of pre-alloyed powder and used as a model material in investigating the influences of heat treatment on the thermal properties of the material. In the as-extruded samples, fine Si particles are distributed uniformly in the Al matrix. When the alloy is annealed at 250 °C or 400 °C for 2 h, neither the Al nor Si grains grow significantly, but the internal strain developed in extrusion is relieved. Therefore, thermal conductivity is improved to 148.0 W/(m·K) and the coefficient of thermal expansion is reduced to 17.3 × 10−6/K. With further increasing annealing temperature to 560 °C, the coarsening of Al and Si grains occurs. On one hand, it significantly reduces the grain boundaries and phase boundaries in the material, consequently further increasing the thermal conductivity to 174.8 W/(m·K). On the other hand, the coarsened structures lead to thermal stress during cooling, which offsets the constraining effect of Si on the thermal expansion of Al and results in an increase in the coefficient of thermal expansion. • Fabricating Al-20Si alloy with good thermal properties by powder extrusion • Investigating microstructures by combined technology of EBSD and EDS • Studying the effects of annealing on microstructures and thermal properties • Revealing the internal stress generated in sample cooling and its effects on CTE [ABSTRACT FROM AUTHOR]