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In the present research, the microstructures and mechanical properties of Al–Si–Cu alloy matrix composites reinforced with nanosized alumina (Al2O3) and zirconia (ZrO2) were investigated. For this purpose, Al2O3 particulates were replaced with different wt% of ZrO2 to improve microstructure and mechanical properties. The T6 heat treatment was also performed to investigate mechanical properties in heat-treated condition. Tensile testing, hardness measurement, optical microscopy, x-ray diffraction (XRD), energy dispersive spectroscopy, and scanning electron microscope examination were used to characterize the behavior of composite and matrix. The highest tensile strength was achieved in the specimen containing 1.25 wt% ZrO2 and 0.75 wt% Al2O3, which shows an increase to 36% in comparison with the nonreinforced base alloy. The hardness values indicated 11% increase following the heat treatment. Fracture surface examinations revealed a transition from ductile fracture mode in as-cast aluminum alloy to rather brittle in Al–Si–Cu alloy matrix hybrid composites. [ABSTRACT FROM PUBLISHER]

The size parameters of 6061 aluminum alloy rib-web forging were optimized by using hot-processing map and finite element method (FEM) based on high-temperature compression data. The results show that the stress level of the alloy can be represented by a Zener-Holloman parameter in a hyperbolic sine-type equation with the hot deformation activation energy of 343.7 kJ/mol. Dynamic recovery and dynamic recrystallization concurrently preceded during high-temperature deformation of the alloy. Optimal hot-processing parameters for the alloy corresponding to the peak value of 0.42 are 753 K and 0.001 s. The instability domain occurs at deformation temperature lower than 653 K. FEM is an available method to validate hot-processing map in actual manufacture by analyzing the effect of corner radius, rib width, and web thickness on workability of rib-web forging of the alloy. Size parameters of die forgings can be optimized conveniently by combining hot-processing map and FEM. [ABSTRACT FROM AUTHOR]

In the present study, the relationship between structural and mechanical properties of friction stir processed Al-1100 alloy and process parameters (tool rotation rate: ω and traverse speed: ν) was studied to get an better understanding and optimizing the friction stir processing (FSP) condition of this alloy. Microstructural studies revealed that increasing of ω up to 720 rpm resulted in grain refinement in the stirred zone (SZ), but higher increasing of ω caused grain growth in this zone. These variations of SZ grain size illustrated that the prevailing factor that determined the SZ grain size was plastic deformation at first and thereafter, peak temperature in the SZ. Mechanical properties investigations were in accordance with microstructural findings and illustrated that optimized FSP condition for Al-1100 alloy was 720 rpm and 20 mm/min. Optimized FSP condition resulted in a significant improvement of tensile strength and elongation up to 22 and 8% of those of base metal, respectively. [ABSTRACT FROM AUTHOR]

In this paper, AA 2024 T3-rolled sheets were joined in butt joint configuration through the friction stir welding process. Different joints were carried out varying the principal process parameters (i.e., tool welding speed and tool rotational speed). The aim of this work was the study and the experimental characterization of the influence of the process parameters on the forces acting on the tool during the FSW process. Furthermore, it was studied the correlation between the forces and the grain size, in particular with the extension of the heat-affected zone. Forces acting along the axis parallel to the tool are actually greater than those acting along welding direction. All the recorded forces are strictly dependant on the process parameters adopted. No correlation has been found between the grain dimension within the weld bead and the recorded forces, while the greater the forces, the narrower the extension of the heat-affected zone. [ABSTRACT FROM AUTHOR]

A model was developed to predict thickness and continuity of β phase (AlMg) formed at grain boundaries of long-term aged Al 5083 alloy. In this model, a variable collector plate mechanism was adopted at the early stage of aging, then, at about 1 month ( $$ 2\sqrt {D_{\text{b}} t} \approx 100\;{\text{nm}} $$ ), the model transitions to a constant collector plate mechanism. Two concentration profiles of Mg, one for a semi-infinite bulk at short diffusion distances and one for a finite slab at long diffusion distances ( $$ 2\sqrt {D_{\text{m}} t} \approx 20\,{\text{pct}} $$ of the grain size), were applied to this model for different aging times. Capillarity effects were used to determine the morphology of β phase at the grain boundary. Combining different collector plate mechanisms and Mg concentration profiles, the whole β phase growth process was divided into three stages (short-term Mg concentration profile-variable collector plate, short-term Mg concentration profile-constant collector plate, and long-term Mg concentration profile-constant collector plate). Finally, the model was solved numerically. Experimental results of β phase length and thickness were obtained using transmission electron microscopy (TEM) images of Al 5083 aged at 343 K (70 °C) for different thermal exposure times. Modeling results of β phase thickness and continuity agree well with experimental observations. [ABSTRACT FROM AUTHOR]

In this work the effect of heat treatment on the structure and the durability of double layer Ni/Al coatings was investigated. An initial Ni–Cr layer was primarily deposited by thermal spray, followed by a successive Al metallic layer in a second stage. The specimens were then heat treated in inert atmosphere. Nickel aluminide compounds were formed as a result of the diffusion between the two layers upon annealing. Indeed, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy examinations of the coated samples revealed that the as sprayed coatings contain two distinct Al and Ni–Cr layers while the heat treated coatings were gradually transformed to Al 3 Ni depending on the heat treatment parameters. The as sprayed and annealed specimens were tested by subjecting them in an air environment at 700 °C and 800 °C, for the evaluation of their durability and resistance. It was found that the annealed samples have superior high temperature resistance compared with the as sprayed coatings and bare steel, which is attributed to the presence of Ni–Al compounds, to the low coating porosity and to the formation of dense oxides on the coating surface. [ABSTRACT FROM AUTHOR]

The effect of Al additions on grain refinement of Mg-Gd-Y alloys with different solute contents at different cooling rates has been investigated. For all alloys, significant grain refinement was due to the formation of Al(GdY) nucleant particles. The number density and size distribution of Al(GdY) were affected by both solute content and the cooling rate. Grain sizes ( d) of Mg-Gd-Y base alloys and of Mg-Gd-Y-Al alloys were related to solute content (defined by the growth restriction factor, Q), cooling rate ( $$ \dot{T} $$ ), and area number density ( ρ) and size ( d) of nucleant particles that can be activated. It is found that grain sizes of Mg-Gd-Y base alloys follow the relationship $$ d_{\text{gs}} = a + \frac{b}{{Q\sqrt {\dot{T}} }} $$ , while grain sizes of Al-refined samples follow the relationship $$ d_{\text{gs}} = \frac{a'}{{\sqrt {\rho {}_{\text{ns}}} }} + \frac{b'}{{\sqrt {\dot{T}} Qd_{\text{p}} }} $$ , where a, b, a′, and b′ were constants. In addition, the grain refinement effect of Al additions was more susceptible to solute content and the cooling rate than that of Zr which is regarded as the most efficient grain refiner for Mg alloys. [ABSTRACT FROM AUTHOR]

The scope of this investigation is to evaluate the effect of welding parameters on the mechanical properties and microstructural features of 3-mm-thick AA7075-T6 aluminum alloy subjected to gas heating system as a preheating source during friction stir welding. Toward this end, a gas heating system was designed to heat up the weld seam just ahead of rotating tool to soften the material before being stirred. Three welding parameters, five levels, and a central composite design (CCD) have been used to minimize the number of experimental conditions. The joining parameters such as tool rotational speed, welding speed, and shoulder diameter have a significant influence on determining the mechanical properties of the welded joints. It was found that using preheating system mostly can result in higher total heat input into the weld joint and effectively reduces the formation of defects when unsuitable process parameters were used. Also, an attempt has been made to establish the mathematical model to predict the tensile strength and microhardness of the joints. The optimal welding conditions to maximize the final responses were investigated and reported. The results show that the joint fabricated at a rotational speed of 1,050 rpm, welding speed of 100 mm/min, and shoulder diameter of 14 mm exhibited higher mechanical properties compared to other joints. [ABSTRACT FROM AUTHOR]

The use of Al engine blocks has increased significantly to improve vehicle fuel efficiency. However, the gray cast iron cylinder liners cause the development of large tensile residual stress along the cylinder bores which necessitates the optimization of mechanical properties in this region to prevent premature engine failure. This study compared the microstructure of T4-treated Al billet castings of varying cooling rate to that of the cylinder region of T4-treated (current production schedule) Al engine blocks. The aim of this study was to develop a cost-effective small scale heat treatment optimization method for engine block production. Comparisons in microstructure between the engine block and the billet castings were carried out using optical and scanning electron microscopy. The results suggest that the microstructure and hardness at the top, middle, and bottom of the cylinder were similar to those of each representative billet casting, indicating that heat treatment resulted in successful replication of the engine block locations. In addition, tensile testing revealed that the YS and UTS increased slightly following T4 treatment for all billet castings, which was also observed at the middle of the engine block cylinder bridge. As such, this method can be an effective forerunner for future heat treatment optimization in Al engine block production. [ABSTRACT FROM AUTHOR]

An ultrahigh strength silicon carbide particle reinforced aluminium matrix composite (SiCp/Al), in which the volume of SiC particles was ∼15% and the initial size was ∼10 μm, was prepared using a spray deposition technique, and then hot extrusion and equal channel angular pressing (ECAP) were performed on the composite to investigate the evolution of microstructures and mechanical properties. Microstructural observations revealed that homogeneous equiaxed grains were obtained and the grain size was reduced from ∼3·0 μm to ∼400 nm after four passes of ECAP using route Bc. SiC particles were broken from ∼10 to ∼2 μm sized fragments by the huge shear stress, and many cavities between the broken SiC particles developed; these cavities derived from the broken SiC particles were filled with the Almatrix. Following T6 heat treatment (comprising solution heat treatment and then artificial aging), the microstructure of the equal channel angular pressed SiCp/Al composite showed a very high stability; the tensile strength, yield strength, modulus and elongation of the composite were 770·0 MPa, 575·0 MPa, 106·6 GPa and 7·4% respectively. [ABSTRACT FROM AUTHOR]

7050 aluminium alloy metal matrix composites reinforced with different weight fractions of Al3Ti particles were fabricated using an in situ synthesis method and subsequent rolling, solution and aging treatment. The effects of Al3Ti particle content and particle size on the microstructures and mechanical properties of the composites were investigated by means of hardness measurements, optical microscopy and electron probe. We concluded that the grain size of the composites was smaller than that of the matrix alloy, and with an increase in the plastic deformation, the dispersion of particles was more uniform and fine. It was also found that the hardness of the composites increases with increasing weight fraction and decreasing particle size. By increasing the plastic deformation, the hardness of both the composites increased first and then decreased with the following deformation. In addition, the heat treatment contributed to the hardness. [ABSTRACT FROM AUTHOR]

Highlights: [•] T4 heat treatment and the addition of Li modify the microstructure of alloy. [•] Heat treatment improves the tensile properties of non-modified and modified alloys. [•] Fracture surfaces of modified specimens had more ductile dimples than base alloys. [ABSTRACT FROM AUTHOR]

Highlights: [•] Only two kind Fe-rich intermetallics are found in the heat-treated Al–5.0Cu–0.6Mn–xFe alloys. [•] Squeeze cast Al–5.0Cu–0.6Mn alloys containing 1.5% Fe have desirable mechanical properties. [•] The difference between gravity die cast and squeeze cast Al–5.0Cu–0.6Mn–xFe alloys. [ABSTRACT FROM AUTHOR]

ABSTRACT A controlled overaging process is proposed to increase region II fatigue crack propagation resistance of 2024-T3 aluminium alloy. Overaging was achieved by subjecting the material from the initial T3 state to heat treatment at specific aging temperatures resulting in substantial reduction in hardness. Fatigue crack growth tests were subsequently performed in the intermediate Δ Κ region to assess the influence of aging treatment on fatigue crack propagation rate. The experimental results showed that overaging at high temperatures enhances the fatigue crack growth resistance of the material with regard to initial T3 state. Fatigue crack growth rates were found to decrease with increasing overaging temperature. Cyclic stress strain tests were performed to assess the impact of the performed overaging on cyclic behaviour. The results revealed that cyclic strain hardening is enhanced in the overaged material, contributing to increased fatigue crack closure levels. [ABSTRACT FROM AUTHOR]

In this study, dissimilar AA7075-O/6061-O and AA7075-T6/6061-T6 butt joints were produced by friction stir welding (FSW), and postweld heat treatment (PWHT) was applied to the joints obtained. The effects of initial temper condition and PWHT on the microstructure and mechanical properties of the dissimilar joints were thus investigated. It was demonstrated that sound dissimilar joints can be produced for both temper conditions. A hardness increase in the joint area ( i.e., strength overmatching) was obtained in the joints produced in the O-temper condition, whereas a hardness loss was observed in the joint area of the joints obtained in the T6 temper condition. It was also well demonstrated that PWHT could be used in order to improve the joint properties for both O and T6 joints provided that the joint is defect-free prior to subsequent heat treatment. [ABSTRACT FROM AUTHOR]

We demonstrate experimentally that a part-per-million addition of Sn solutes in Al-Mg-Si alloys can inhibit natural aging and enhance artificial aging. The mechanism controlling the aging is argued to be vacancy diffusion, with solutes trapping vacancies at low temperature and releasing them at elevated temperature, which is supported by a thermodynamic model and first-principles computations of Sn-vacancy binding. This "diffusion on demand" solves the long-standing problem of detrimental natural aging in Al-Mg-Si alloys, which is of great scientific and industrial importance. Moreover, the mechanism of controlled buffering and release of excess vacancies is generally applicable to modulate diffusion in other metallic systems. [ABSTRACT FROM AUTHOR]

The microstructures and properties of 2024 and 7A09 aeronautical aluminium alloys subjected to thermal cycling have been investigated in simulated low earth orbit (LEO) space environment using microhardness tests, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microhardness tests revealed that the hardness decrease first and then increase, but finally decrease with the cycle times. The results of XRD and TEM show that, in 2024 aluminium alloy, the precipitate evolution with the cycling time is the small needle-like S′ phases transforming to the rod-like equilibrium S phases. In 7A09 aluminium alloys, needle-like η′ phases and short rod-like η equilibrium phases transform to rod-like η equilibrium phases and large size of Guinier-Preston zones in the process of thermal cycling. Furthermore, many cavities around the precipitated phase appear after 500 cycles in both 2024 and 7A09 aluminium alloys. The relationship between microstructural evolution and thermal fatigue in LEO space environment was discussed. [ABSTRACT FROM AUTHOR]

Submitted article deals with influence of iron based phases segregation by nickel, which is in literature known as iron based phases corrector. Iron is one of the most common impurities that can be found in Al-Si alloys. It is impossible to remove iron from melt by standard operations, but it is possible to eliminate iron negative effects by addition of other elements, that enables segregation of iron in form of intermetallics with less harmful effect. For melt treatment was selected an exact alloy with requested iron content - master alloy AlNi20. Influence of nickel was evaluated quantitatively by chemical analysis (solubility), thermal analysis and microstructure evaluation. Experimental results analysis shows a new view on solubility of iron based phases during melt preparation and treatment with higher iron content and also nickel effect as iron corrector of iron based phases. It can be concluded that nickel did not influenced iron based phases (β-phases), it does not change their type into more favorable form. As an initial impulse for starting this work was insufficient theoretical knowledge of usage secondary alloys Al-Si-Cu with higher iron content and its appropriate elimination in process of castings production for automotive industry. Increased iron content in alloys causes segregation of iron phases in various shapes and types during solidification, which subsequently affects quality, soundness and lifetime of castings. Because of increased demands for casting quality, final mechanical properties and effort to reduce costs, it is necessary to look for compromises in casting production from secondary alloys with occurrence of various impurities. [ABSTRACT FROM AUTHOR]

The mechanical properties of different aluminium alloys used in the manufacture of power train automotive parts were studied. The alloys were cast in wedge shape ingots that promote a one-dimensional solidification gradient. Tensile samples were machined from bars that were cast with different degrees of microstructural refining and were heat treated at times and temperatures that depended on their composition. The mechanical properties were measured from samples that had been held for 200 h within the temperature range of 25 to 300°C. It was found that the increase of Cu in alloys of the Si-Mg type alloys enhanced the mechanical properties above room temperature. The best properties were found in the Al-Cu alloy. [ABSTRACT FROM AUTHOR]

In the present study, 7005 aluminum alloy billets were supplied in the warm extruded and T6 heat treated state. They were then reheated to the semisolid state and the microstructural evolution and coarsening investigated. This is necessary groundwork if the billets are to be formed to shape by semisolid processing, an innovative manufacturing route which has recently gained wide use for a range of aluminum alloys but which has not yet been applied to 7005. The results showed that the average spheroid size, liquid film thickness and liquid fraction of 7005 aluminum alloy increased with increase in soaking time. Intragranular liquid droplets were present in solid grains, and coarsened with increase in soaking time and isothermal temperature. The roundness of globules of solid in the semisolid state at 600°C–615°C was in the range of 1.5 to 2.0 after soaking for periods up to 12min at 620°C, but for times greater than 15min was more than 2, which is unlikely to be suitable for the semi-solid forming process, where smooth flow is required and therefore relatively round globules. When the isothermal temperatures were 600°C, 610°C, 615°C and 620°C, the coarsening rates were 542μm3 s−1, 606μm3 s−1, 683μm3 s−1 and 688μm3 s−1, respectively. The coarsening rate K increased with the increase of isothermal temperature. These values place this alloy on the dividing line between typical coarsening rates for normally cast alloys and typical coarsening rates for normally wrought alloys. This is attributed to the fact that the alloy has a relatively simple precipitation hardening system in comparison with other 7xxx alloys and the hardening precipitate (MgZn2) melts below the temperature the experiments have been carried out at, hence preventing the precipitates inhibiting liquid film migration and diffusion along narrow liquid films at spheroid boundaries. Coarsening tends to occur via Ostwald ripening and coalescence, but Ostwald ripening plays an increasing role with the increase of isothermal temperature. [ABSTRACT FROM AUTHOR]

Abstract: Anodized films of aluminum alloys are composed of an inner thin barrier layer and an outer thick porous layer. A sealing process as a post treatment of anodizing, the porous layer achieves improved mechanical and chemical performance as well as decorative color. Nevertheless, dramatically increased hardness could not be achieved using traditional sealing processes. In this study, the sealing of anodized aluminum alloy was carried out by repetition of dipping in a hexavalent chromium oxide solution and heat treatment. The changes in the anodized layer before and after the sealing were analyzed by XRD and SEM. Electrochemical corrosion and wear rate test were also carried out. The hardness, wear resistance and corrosion resistance were compared with traditional sealing methods, such as boiling water and cold nickel fluoride. By heat treatment after dipping in a hexavalent chromium oxide solution, Cr2O3 was formed and filled the pores in the porous layer of the anodized film. Therefore, the hardness of the anodized film was increased with an improvement in wear resistance. In addition, improvement in corrosion resistance was achieved by Cr2O3 sealing. [Copyright &y& Elsevier]

The experimental attempts were effectuated in order to determine the hardness values, respectively to highlight the structure of the AlCu4PbMgMn alloy in different conditions of heat treatment. The experimental tests were performed on the AlCu4PbMgMn alloy, the hardening temperatures were between (500- 530)° C and the alloy was also subjected to artificial aging. The artificial aging was done in a magnetic field (stationary and alternative) and a vibrating one.The efficiency of same thermic treatment depends on a series of factors, some depending on the material and others on the work parameters. The optimum variant or variants can be obtained by joining in a correct way the chemical composition with the parameters values of the heat treatments and supplementary with some utilization factors of stimulating the process at the net crystalline level. [ABSTRACT FROM AUTHOR]

Abstract: The hot deformation behavior of homogenized AA7150 aluminum alloys containing different Zr contents (0–0.19wt%) was studied in uniaxial compression tests conducted at various temperatures (300–450°C) and strain rates (0.001–10s−1). Microstructural evolution was investigated using an optical microscope, a field-emission gun scanning electron microscope, a transmission electron microscope and the electron backscattered diffraction technique. The results reveal no significant variation in the peak flow stress or activation energy between the 7150 base alloy and the alloy containing 0.04% Zr. With a further increase in the Zr content to 0.19%, the values of peak flow stress and activation energy increased significantly. The materials constants and activation energy for hot deformation were determined from the experimental compression data obtained for all alloys studied. The solved constitutive equations yielded good predictions of the peak flow stress over wide temperature and strain-rate ranges for 7150 alloys with different Zr contents. The dynamic recovery level of the materials was reduced after being alloyed with Zr, which was associated with a decrease in the mean misorientation angle of boundaries and a decrease in subgrain size. The addition of Zr promoted the retardation of dynamic recovery and the inhibition of dynamic recrystallization during hot deformation due to the pinning effect of Al3Zr dispersoids on dislocation motion and to restrained dynamic restoration. [Copyright &y& Elsevier]

Abstract: The effects of temperature on the dynamic yield and spall behaviors of two aluminum alloys, 2024-T4 and 7075-T6, were investigated using plate-impact spall experiments, including real-time measurements of free surface velocity. A heating device was designed that was coupled to a light gas gun. Hugoniot elastic limit (HEL) strength and spall strength were calculated using the free surface velocity profiles. Normalized HEL strength and normalized spall strength of 2024-T4 and 7075-T6 exhibited a similar linear decrease with increasing temperature. Comparison of aluminum alloys and pure aluminum demonstrated differences in the correlation of HEL strength and spall strength. This difference was linked to the different underlying mechanisms of damage. [Copyright &y& Elsevier]

Abstract: The isothermal deformation compression tests of AA7085 aluminum alloy were performed on Gleeble-1500 system in the temperature range from 250°C to 450°C and at strain rate range from 0.01s−1 to 10s−1. The microstructure of samples was observed using optical microscopy (OM) and transmission electron microscopy (TEM) techniques. The results show that the peak stress levels decreased with the increase of deformation temperatures or the decrease of strain rate, which can be represented by the Zener–Hollomon parameter in the exponent-type equation with the hot deformation activation energy of 249.11KJ/mol. Dynamic recrystallization more obviously occurred in the sample with higher Z value than in the sample with lower Z value. Dynamic recrystallization is sensitively dependent on the deformation temperature. [Copyright &y& Elsevier]

Al-Al13Fe4-Al2O3-TiB2nanocomposite powder was fabricated by mechanical alloying (MA) and subsequent heat treatment of aluminum, ferrotitanium and boron oxide as a raw material. The obtained nanocomposite powder was evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Also; microhardness values of powder particles after different milling times were measured. Microhardness of this nanocomposite was found to be about 161 HV. The results of XRD showed that the nanocrystalline supersaturated solid solutions of aluminum (α-Al) that formed within 30 h of MA with a mean crystallite size of 12 nm. The above experimental results showed that the heat-treated 30 h of MA powders leads to the in situ formation of nanocrystalline TiB2in an Al matrix with a mean crystallite size of 45 nm. It was also found that after the heat treatment, moreover, the TiB2phase, the other compounds such as Al2O3and Al13Fe4have been formed. [ABSTRACT FROM AUTHOR]

Magnesium alloys are attracting great interest from the automotive industry because of the potential for weight reduction. An AZ91D cast alloy was studied in the current work to understand the effect of heat treatment on the microstructure and dynamic compressive properties. The selected heat treatments include solution treatment (T4) and solution treatment followed by aging (T6). The as-cast alloy microstructure consists of intermetallic β-phase (MgAl) precipitates surrounded by α + β lamellar eutectic in α-Mg solid solution. The AZ91D-T4 specimens showed small β-phase precipitates along the grain boundaries and regions of eutectic mixture. The T6 heat treatment causes the β-phase platelets in the α + β eutectic to grow and develop into β-precipitates. The difference in the phase morphology reflects into the mechanical properties. The Vickers hardness of the T6 heat-treated specimens was 3.6% higher than the as-cast alloy. The compressive yield strengths of T4 and T6 treated specimens were 1.3% and 43.1% higher than those of as-cast specimens. The high strain rate compression testing resulted in increase in the strength with strain rate for the T4 and T6 specimens. A maximum increase of 42% was observed in T6 specimen tested at a strain rate of 4,000/s in comparison to the quasi-static compression. Under high strain rate compression testing, the T6 heat-treated specimens showed failure of the β-precipitates resulting in increased energy absorption in comparison to the quasi-static compression. [ABSTRACT FROM AUTHOR]

The direct thermal method is used for the creation of globular microstructures suitable for semi-solid metal forming. In this paper, both simulation and experimental results using direct thermal method are presented. ProCAST® software was used to estimate temperature distribution inside the aluminum billet. In validation work, molten aluminum A356 was poured into metallic copper tube molds and cooled down to the semi-solid temperature before being quenched in water at room temperature. The effect of pouring temperatures of 630°C, 650°C, 665°C, 680°C and holding times of 45s and 60s on the microstructure of aluminum A356 alloy were investigated. The simulation results showed that the average temperature rate within the copper mold, from initial pouring temperature to just before quenching, was approximately 1°C/s. Examination of the solidified microstructures showed that the microstructure was more spherical when lower pouring temperatures and holding periods were used. From the micrographs it was found that the most globular and smallest structures were achieved at processing parameters of 630°C and 45s. [ABSTRACT FROM PUBLISHER]

In this study, the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of friction stir butt-joined AA6061 Al-alloy plates both in O and T6-temper conditions was investigated by detailed microstructural investigations and microhardness measurements, in combination with transverse tensile testing. It was determined that the PWHT might result in abnormal grain growth (AGG) in the weld zone particularly in the joints produced in O-temper condition depending on the weld parameters used during friction stir welding. The PWHT generally led to an improvement in the mechanical properties even if AGG took place. Thus, the post-weld heat-treated joints exhibited mechanical properties much higher than those of respective as-welded plates and comparable to those of the respective base plates. [ABSTRACT FROM AUTHOR]

Phase transformations in aluminum alloys 1424 and V-1461 are investigated. Special features of the structure of the δ′-phase in the initial stages of aging of alloy 1424 are determined with the help of x-ray diffraction analysis and transmission electron microscopy. The earlier plotted diagram of aging-induced phase transformations (AIPT) of alloy 1424 is amended. The temperature and time ranges of the existence of the phases are determined and an AIPT diagram is plotted for alloy V-1461. It is shown that the maximum strength properties of alloy V-1461 are implemented in phase domains (δ′ + θ′ + $$ {{T^{\prime}}_1} $$ + S′) and (δ′ + $$ {{T^{\prime}}_1} $$ + S′). This makes it possible to obtain various phase compositions corresponding to the required combination of properties and substantiates the use of multistage aging modes. [ABSTRACT FROM AUTHOR]

Fracture surfaces of aluminum alloys VAD23, AK6, V95, 01911, 1420, 1430, 1440, 1451 are studied after different variants of aging. Common features of formation of fractures are determined depending on the modes of heat treatment, conditions of deformation and presence of impurities in the aluminum alloys. Efficiency of the use of fractography for estimating the working capacity of the aluminum alloys is demonstrated. [ABSTRACT FROM AUTHOR]

The influence of initial texture on rollability is investigated using cuneal AZ31 Mg alloy sheets. Upon large thickness reduction, the sheet with initial basal texture has many edge cracks, whereas the sheet is crack-free if its normal direction is orthogonal to c-axis of hexagonal close packed (HCP) lattice. Microstructural analysis shows that the former one has heterogeneous grain structure owing to grain-boundary-related recrystallization, and by contrast the later one has a more uniform microstructure for the twin-related recrystallization. The initial nonbasal texture can lead to excellent rollability and anisotropic deformation, based on which a new iterative approach of rolling is proposed, which may achieve large reduction in few passes. [ABSTRACT FROM AUTHOR]

The experimental stress-strain data from isothermal hot compression tests, in a wide range of temperatures (350-500 °C) and strain rates (0.005-0.5 s-1), were employed to develop constitutive equations in a commercially pure aluminum (AA1070). The effects of temperature and strain rate on the hot deformation behavior were represented by Zener-Hollomon parameter including Arrhenius term. The results show that the hardening rate and flow stress are evidently affected by both deformation temperature and strain rate. The power law, exponential, and hyperbolic sinusoidal types of Zener-Hollomon equations were used to determine the hot deformation behavior of AAI070. The results suggested that the highest correlation coefficient was achieved for the hyperbolic sine law for the studied material. So the proposed deformation constitutive equations can give an accurate and precise estimate of the flow stress for AA1070, which means it can be used for numerical simulation of hot forming processes and for choosing proper forming parameters in engineering practice accurately. [ABSTRACT FROM AUTHOR]

Abstract: The damage introduced by compressive deformation at room temperature and 300°C in three cast AlSi alloys with different additions of Cu and Ni is investigated by synchrotron X-ray microtomography. The same damage mechanisms are identified for all alloys independent of the heat treatment and test temperature: fracture of aluminides, fracture of eutectic Si, debonding between Si and Al-matrix, debonding between aluminides and Al-matrix and fracture of primary Si. The volume fraction of damage decreases with solution treatment time and deformation temperature due to the partial spheroidisation of rigid phases and increase in flowability of the matrix, respectively. The morphology of voids is quantified in terms of their three-dimensional aspect ratio and is correlated with their orientation to obtain information on the load carrying capability of the networks formed by Si and aluminides. [Copyright &y& Elsevier]

In the case of duralumin complex compounds have been identified as: Mg2Si, Al2CuMg, Al7Cu2Fe, etc.This indicates structural complexity for duralumin due to the extensive alloying, complexity that generates multiple factors influence the mechanical, functional, tribological properties. This paper studies the influence of alloying compounds in the emergence hardening phases in aluminum alloys 2024, special destinations use. [ABSTRACT FROM AUTHOR]

Abstract: How microstructures evolve in heat-treatable aluminum alloys during multi-layer friction deposition is an intriguing question. The current work shows that the process invariably leads to overaging of strengthening precipitates in such materials as alloy 2014. The problem can be overcome using a solution treatment, but it can lead to other problems such as abnormal grain growth. Based on these findings, it appears that the benefits of friction deposition cannot be fully realized in heat-treatable aluminum alloys. [Copyright &y& Elsevier]

The effect of heat treatment of the plastically worked 7000 series Al-Zn-Mg aluminium alloy system on its stress-corrosion resistance is examined. For the same chemical constitution, the effect of heat treatment on mechanical and corrosion properties of Al-Zn-Mg alloys systems is remarkable. It was proved that a parameter having significant effect on corrosion properties of the alloy is the rate of alloy cooling after heat treatment. This conclusion is confirmed by observation of structural forms which fully reflect mechanical and corrosion properties of the alloy. [ABSTRACT FROM AUTHOR]

Abstract: The influence of precipitate microstructure on fracture mechanisms is studied in a recently developed Al–Cu–Li alloy, AA2198. The intra-granular and inter-granular microstructures are varied independently by changing the quench rate from the solution heat treatment, the amount of pre-stretching and the heat treatment time. Fracture toughness is evaluated by short bar chevron tear tests that make possible to evidence clearly the mechanisms of inter-granular fracture. It is shown that intergranular ductile fracture significantly occurs in all conditions of heat treatment where substantial precipitation has taken place. This mechanism is mainly controlled by the state of inter-granular precipitation and plays a major role to determine the value of transverse fracture toughness, while the strength and ductility of the alloy are mainly controlled by the state of intra-granular precipitation. [Copyright &y& Elsevier]

Abstract: In this study, machined chips of Al 7050 alloy derived from the aeronautic industry were reprocessed by spray forming technique and hot extrusion. The microstructures and hardness of the deposit and their subsequent development resulting from heat treatment and hot extrusion were investigated. The results show that spray forming contributed to providing a refined and homogeneous microstructure after aging heat treatment at 121 °C for 16 h due to a homogeneous distribution of the hardening η′ metastable phase. [Copyright &y& Elsevier]

Stress corrosion cracking studies of aluminum alloys AA2219, AA8090, and AA5456 in heat-treated and non heat-treated condition were carried out using electrochemical noise technique with various applied stresses. Electrochemical noise time series data (corrosion potential vs. time) was obtained for the stressed tensile specimens in 3.5% NaCl aqueous solution at room temperature (27 °C). The values of drop in corrosion potential, total corrosion potential, mean corrosion potential, and hydrogen overpotential were evaluated from corrosion potential versus time series data. The electrochemical noise time series data was further analyzed with rescaled range ( R/ S) analysis proposed by Hurst to obtain the Hurst exponent. According to the results, higher values of the Hurst exponents with increased applied stresses showed more susceptibility to stress corrosion cracking as confirmed in case of alloy AA 2219 and AA8090. [ABSTRACT FROM AUTHOR]

This paper reports on the effect of artificial aging on the machinability of Al-7Si-Mg (A356) cast alloys for the as-received alloy, solution heat-treated (SHT) alloy and then aged SHT alloy at 155, 180, and 220 °C, respectively. The influence of heat treatment on the machinability of the alloys studied was considered using innovative criteria such as dust emission. The effect of various lubrication modes including dry, mist, and wet process, as well as cutting speed and feed rate, was also investigated. The results obtained from the statistically designed experiments indicate that at the same cutting conditions, the A356-T7 heat treatment generates less dust emission level compared to other various heat treatments (there is 32% less airborne swarf produced than with A356-T6). Aging at low temperature was observed to produce the greatest level of the dust emission while the aging at higher temperatures is accompanied by a reduction in the dust emission level. Fracture surface analysis using scanning electron microscope, has shown that dust emission levels were strongly dependent on the nature of the fracture surface of the alloys studied, with different heat treatments. A change in chip formation was also found to be a function of age hardening and dust emission during machining of the tested aluminum alloy. A correlation was established between the cutting speed, the feed rate, and the dust emission, which is useful for determining the conditions required for minimal dust emission. [ABSTRACT FROM AUTHOR]

The current study proposes a simple constitutive model that integrates the kinetics of precipitation during static aging and the kinetics of precipitate dissolution during preheating to deformation temperature to predict the hot flow behavior of AA6063 alloy. The model relates the flow behavior of the age-hardenable alloy to the alloy chemistry, thermal history as well as deformation temperature, strain, and strain rate by means of a physically based model. Different aging conditions, including supersaturated solid solution and overaging conditions with different deformation parameters, were assessed. Each part of the model was in good agreement with those of experimental and other model results published in the literature. [ABSTRACT FROM AUTHOR]

The evolution of the microstructure of an AlMg4.7Si8 alloy is investigated by scanning electron microscopy and ex situ synchrotron tomography in as-cast condition and subsequent solution treatments for 1h and 25h at 540°C, respectively. The eutectic Mg2Si phase, which presents a highly interconnected structure in the as-cast condition, undergoes significant morphological changes during the solution heat treatment. Statistical analyses of the particle distribution, the sphericity, the mean curvatures and Gaussian curvatures describe the disintegration of the interconnected seaweed-like structure followed by the rounding of the disintegrated fractions of the eutectic branches quantitatively. The ternary eutectic Si resulting from the Si-surplus to the stoichiometric Mg2Si ratio of the alloy undergoes similar changes. The morphological evolution during solution heat treatment is correlated with results of elevated temperature compression tests at 300°C. The elevated temperature compressive strength is more sensitive to the degree of interconnectivity of the three dimensional Mg2Si network than to the shape of the individual particles. [ABSTRACT FROM AUTHOR]

Curves of flow of alloys of the Al – Mg, Al – Zn and Al – Cu systems are obtained for the temperature range of 200 – 500°C at deformation rates from 0.1 to 30 sec –1. A mathematical model of the dependence of the flow stress of the alloys on the temperature and rate parameters of the deformation is designed, which makes it possible to compute flow stresses with an error of 5%. [ABSTRACT FROM AUTHOR]

The effect of Fe and Ni on the parameters of superelasticity of alloy Al – 11% Zn – 3%Mg – 0.8% Cu – 0.3% Zr is studied. It is shown that addition of 1% Ni and 0.6% Fe raises the volume fraction of second-phase particles from 6 to 14%, and this provides a more dispersed and partially recrystallized structure. As a result, the flow stress during superplastic deformation decreases by a factor of 1.5 – 2.0 and the elongation increases from 360 – 420% to 500 – 660% at deformation rates ranging within 2 × 10 −3 – 1 × 10 −2 sec −1. [ABSTRACT FROM AUTHOR]

Solution and aging treatments are important approaches to improve mechanical properties and microstructure of aluminum-base alloys. In this research, a new type high strength Al-Cu-Si-Mn cast alloy was prepared. The effect of different solution and aging treatment temperatures on microstructure and mechanical properties of the Al-Cu-Si-Mn cast alloy were studied by means of microstructure observation and mechanical properties testing. Results showed that after solution treated at different temperatures for 12 h and aged at 175 °C for 12 h, with the increase of the solution temperature, both the tensile strength and the elongation of the alloy firstly increase and then decrease, and reach their peak values at 530 °C. When the solution temperature is below 530°C, the microstructure of the alloy consists of α phase, undissolved θ phase and T phase; while when it exceeds 530 °C, the microstructure only consists of α phase and T phase. After solution treated at 530°C for 12 h and aged at different temperatures for 12 h, both the tensile strength and the elongation of the alloy firstly increase and then decrease with the increasing of temperature, and reach their peak values at 175 °C. Therefore, the optimal heat treatment process for the alloy in this study is 12 h solution at 530°C and 12 h aging at 175 °C, and the corresponding tensile strength is 417 MPa, elongation is 4.0%. [ABSTRACT FROM AUTHOR]