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Powder mixture of pure Al and oxidized SiC was consolidated into SiCp/Al composites by equal channel angular pressing and torsion (ECAP-T). The influences of several parameters on the thermal expansions, the thermal conductivities, and the recrystallization temperatures of the as-consolidated composites were studied. These parameters are the number of ECAP-T passes (1, 2, and 4), the content of SiC (10, 20, and 40 wt.%), and the fabrication temperature (150, 250, and 350 °C). The results show that increasing the number of ECAP-T passes has a positive effect on depressing the coefficient of thermal expansion (CTE) of the composite within a certain temperature range, since the total variation amplitude of the CTE is enlarged. The CTE can also be decreased by increasing the content of SiC. The number of ECAP-T passes and the contents of SiC in the composites are both positively related with the thermal conductivity of the composites. No direct relationship between the fabrication temperature and the thermal properties was detected. However, the composite fabricated at too low temperature (150 °C) can not obtain full densification, leading to the appearance of low CTE and thermal conductivity. Finally, when the number of ECAP-T passes is elevated from 2 to 4, the recrystallization temperature of the composite has an obvious declination. [ABSTRACT FROM AUTHOR]

This paper describes a finite element model for predicting the temperature field in high power ultrasonic welding aluminum AA6111 to two dissimilar alloys, magnesium AZ31, and low carbon steel DC04. Experimental thermocouple and other evidence are used to infer the magnitude and distribution of the heat input to the workpiece, as a function of time, for each of the material combinations welded. The resulting temperature histories are used to predict the growth of intermetallic phases at the interface in Al-Mg welds. The microstructural model successfully predicts the thickness of the intermetallic layer, but the sensitivity of the results to temperature is demonstrated. [ABSTRACT FROM AUTHOR]

In order to improve the room temperature ductility and high temperature strength of Fe-25Al alloys, in situ 20 wt.%AlO/Fe-25Al composites with 0, 1, 2, 3, 4, and 5 at.% Cr element contents (0-6.70 wt.%) were prepared by mechanical alloying inducing self-propagating reaction with subsequent plasma-activated sintering. Microstructures, room temperature hardness, flexural strength, fracture toughness, and compression property and wear behavior at mid-high temperatures of the sintered samples were tested and analyzed. The results showed that all the composites with Cr element addition had good microstructure with fine grain size and high relative density. The flexural strength and fracture toughness increased first and then decreased with increasing content of Cr. Especially, the composites with 3 at.% Cr had the highest flexural strength, highest fracture toughness, and best compressive properties during 298-1073 K, and the main fracture mechanism changed from brittle fracture at room temperature to plastic deformation and pullout of the second phase at 673 K. With Cr content increasing, the friction coefficients decreased and the wear rates increased because of decreasing hardness. The composites with 3 at.% Cr had excellent wear properties with lower friction coefficient and wear rate. [ABSTRACT FROM AUTHOR]

We fabricated Mg-Al-Sb alloy by arc melting system. Microstructural analyses were performed and it was found that only MgSb and AlSb phases formed for different heat treatment conditions. The phase transition at 580 °C according to DTA analysis was determined as partial melting and it was supported by phase analyses studies in the literature. The resistivity results showed the metallic and the semiconducting type behavior depending on the heat treatment temperatures. The thermal conductivity measurement was performed in the range of 2-300 K and the data were analyzed by the sum of lattice and carrier components. The thermopower data showed negative and positive values which indicate the sign of total carriers. The linear temperature dependence of thermopower indicates metallic type characteristic of the samples. Mechanical properties of the sample showed two type hardness values dependent on heat treatment temperature. [ABSTRACT FROM AUTHOR]

Isothermal heat treatments in ambient air were performed on wrought Ti–6Al–2Sn–4Zr–2Mo (Ti-6242) material at 500, 593 and 700°C for times up to 500 h. In the presence of oxygen at elevated temperatures simultaneous reactions occurred in Ti-6242 alloy, which resulted in the formation of an oxide scale and a layer with higher oxygen concentration (termed as alpha-case). Total weight gain analysis showed that there was a transition in the oxidation kinetics. At 500°C, the oxidation kinetics obeyed a cubic relationship up to 200 h and thereafter changed to parabolic at prolonged exposure times. At 593°C, it followed a parabolic relationship. After heat treatment at 700°C, the oxidation obeyed a parabolic relationship up to 200 h and thereafter changed to linear at prolonged exposure times. The observed transition is believed to be due to the differences observed in the oxide scale. The activation energy for parabolic oxidation was estimated to be 157 kJ/mol. In addition, alpha-case layer was evaluated using optical microscope, electron probe micro-analyser and microhardness tester. The thickness of the alpha-case layer was found to be a function of temperature and time, increasing proportionally, and following a parabolic relationship. The activation energy for the formation of alpha-case layer was estimated to be 153 kJ/mol. [ABSTRACT FROM AUTHOR]

We have investigated the influence of repetitive near-infrared (NIR) pulsed laser shots in the melting regime on the surface characteristics of an aluminum 6061-T6 alloy. Characteristics of interest include surface morphology, surface roughness, and surface hardness in the melted zone as well as the size of the melted zone. For this study, the proper pulse energy for inducing surface melting at one shot is selected using numerical simulations that calculate the variation in temperature at the laser beam spot for various input pulse energies in order to find the proper pulse energy for raising the temperature to the melting point. In this study, 130 mJ was selected as the input energy for a Nd:YAG laser pulse with a duration of 5 ns. The size of the melted zone measured using optical microscopy (OM) increased logarithmically with an increasing shot number. The surface morphology observed by scanning electron microscopy (SEM) clearly showed a re-solidified microstructure evolution after surface melting. The surface roughness and hardness were measured by atomic force microscopy (AFM) and nano-indentation, respectively. The surface roughness showed almost no variation due to the surface texturing after laser shots over 10. The hardness inside the melted zone was lower than that outside the zone because the β″ phase was transformed to a β phase or dissolved into a matrix. [ABSTRACT FROM AUTHOR]

The evolution of the strengthening precipitate in a precipitation-hardening alloy, such as the gamma prime ( γ′) phase in Ni-base superalloys, during heat treating and welding can affect the resultant mechanical properties significantly. Computational kinetics simulation can be a useful tool for understanding and controlling of such evolution. The present study was conducted to simulate the γ′ precipitation and dissolution during aging and welding of the recently developed Ni-base superalloy 718plus using the PanPrecipitation module of the Pandat software along with available thermodynamic and kinetic databases. The purpose was to demonstrate the application of such software and databases to materials processing including heat treating and welding. The variations in the volume fraction, average precipitation size, and number density of γ′ with time during aging and welding were calculated. The calculated results under aging condition agreed well with the available experimental data, while those under welding also predicted the correct trend. [ABSTRACT FROM AUTHOR]

Aluminium A356 alloy is widely used at automobile and aircraft industries in the form of cast component with varying section size. This study investigates how the microstructure and mechanical properties of different section size vary before and after heat treatment and aging processes. Aluminium ingot is melted using a furnace and poured in to the mold having mold cavities of varying dimensions. Cast components are heat treated as per ASTM standard B917-01 at a temperature of 537 °C for 12 hours followed by a temperature of 155° for 5 hours. In order to investigate the effect of heat treatment and aging processes microstructure and mechanical properties such as impact strength, hardness, and tensile strength were analysed as-cast condition and after heat treatment and aging process. [ABSTRACT FROM AUTHOR]

This work focuses on studying the relationship between the welding and hardening parameters of friction stir welded Al 2024 alloy. The experiments were conducted using Box Behnken design of Response surface methodology. The conducted experiments were then subjected to mechanical testing such as ultimate tensile strength and izod impact tests. Then the identified Least Square hardening model was compared with the welding parameters to explain the relationship between them. The Statistical software “Minitab 16” was used to generate models of the responses. This relation between the identified models of the responses with the welding parameters helps to predict the mechanical property behavior of the friction stir welded Al 2024 alloy. This prediction helps to understand the behavior of the alloy during friction stir welding thereby minimizing the experimental cost and time in the future. [ABSTRACT FROM AUTHOR]

The conventional way of rating the performance of a material subjected to sliding wear is in the form of P – V diagram. The seizing of material is due to changing in the elastic limit and flow stress due to thermal softening and in due course due to cold welding in localized region between the two surfaces. Because of these interactions the allowable pressure decreases with increase in velocity and vice versa. It is to be observed that simply by heat treatment of alloy the seizure resistance is enhanced by 12.5% and further 22.2% by dispersion of 10 wt% of SiCp to alloy. All these facts are discussed on the basis of prevailing wear mechanism. [ABSTRACT FROM AUTHOR]

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]

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 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]

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 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]

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]

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]

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]

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 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]

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]

The effect of preheating on strain rate and liquid flowrate is analysed to develop a model for solidification cracking in successive laser weld spots in 2024 aluminium alloy. It is shown that the lower tendency for solidification cracking with preheating can be attributed to the lower strain rate but not the feeding rate. It is also shown there is a strong tendency for solidification crack propagation through the fusion lines between the consecutive weld spots where there is already a crack present at the fusion line. This observation can be attributed to the higher local strain rate and lower feeding rate. [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 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]

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]

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]

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]

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]

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]

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]

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: 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]

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: 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]

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]