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The strength and wear resistance of aluminium alloys must be improved to enhance their usage in lightweight constructions. Thus, in this study, graphene nanoplates (GNPs) and boron nitride (BN) nanoparticles were reinforced into the Al 5251 aluminium alloy by friction stir processing (FSP). The Al 5251 aluminum alloy sheets were patterned with holes and filled by mono GNPs, mono BN nanoparticles and a hybrid of BN nanoparticles and GNPs. The microstructure, wear, and mechanical properties of the as-received, after FSP, and the manufactured surface nanocomposites were analysed. Wear tests were performed using two methods: weight loss and volume loss methods. FSP led to four times grain refinement. Due to the Zener pinning effect, the reinforcement nanoparticles improved the grain refinement effect by seven times decrease in the mean grain size. The wear rate by volume and weight loss with reinforcing BN nanoparticles decreased by 160 and 1,340%, respectively. Note that the GNP reinforcement insignificantly improved the wear resistance and hardness compared with the BN nanoparticles. The hardness was increased by 50, 120, and 80% by reinforcing the Al 5251 alloy with GNPs, BN, and a hybrid of BN nanoparticles and GNPs, respectively. The nanocomposite reinforced with GNPs exhibited superior mechanical properties compared to the other nanocomposites.

This research is devoted to the microstructure evolution and deformation behavior of the Al-1.2Mg-0.7Si-1.0Cu-0.1Sc-0.2Zr alloy during the isothermal multidirectional forging (MDF) in a large cumulative strain and temperature range. The structure investigation of the studied alloy revealed several phases precipitated during solidification, among which θ(Al2Cu), Q(Al5Cu2Mg8Si6), Mg2Si, Sc-bearing W(AlScCu) and V(AlSi2Sc2) phases were observed. The MDF at 150–350 °C and a maximum cumulative strain of 14.4 significantly refined grain structure providing a mean grain size of 1.2–2.1 µm. The L12 structured Al3(Sc,Zr) dispersoids with a mean size of 10 ± 1 nm were formed during two-step homogenization annealing. Due to Zener pinning of the nanoscale dispersoids and fine-grained structure, the alloy exhibited near-superplastic behavior in a temperature range of 460–500 °C and strain rate range of 2 × 10−3–1 × 10−2 s−1 with the maximum elongation to failure of ~300%. After a strengthening heat treatment, the forged alloy exhibited the yield strength of 326 ± 5 MPa, ultimate tensile strength of 366 ± 5 MPa, and elongation of 10 ± 3%. The hot deformation behavior was described using the Arrhenius type model. The developed model demonstrated high predictability accuracy with a maximum average absolute relative error of 6.6%. [ABSTRACT FROM AUTHOR]

In the present study, AA7075 and AA2024 aluminum alloys were reinforced with ZrC, and the particles of WC were joined using the friction stir welding (FSW) method. The microstructural and mechanical properties of the welds were investigated using SEM, EDS, and tensile tests. The FSW process resulted in high-quality welds with fine grain structure; the stirred zone has 666% smaller grain size than AA7075 and AA2024 aluminum alloys. The tensile test showed strong and ductile welds. The fracture test showed ductile and less brittle composite joints of AA2024 and AA7075 alloys reinforced with WC and ZrC. The processing parameters in the FSW process significantly affect tensile strength (UTS); therefore, the improvement of UTS with tool speed is much greater than with welding speed. Increasing the tool speed from 400 to 560 rpm increased UTS by 7.1%, and from 560 to 700 rpm by 5.4%. The tensile test results showed that the welds exhibited considerable strength and ductility. Fracture analysis showed that the composite joints made of different AA2024 and AA7075 alloys and reinforced with WC and ZrC were ductile and less brittle. This study showed that FSW can efficiently fuse different aluminum alloys reinforced with ceramic particles. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of Friction Stir Processing (FSP) parameters on the microstructure and mechanical properties of an Al-Si7Mg0.2 alloy. The study's findings indicate that augmenting the rotational velocity of the tool in the context of Friction Stir Processing can reduce grain size and enhance the alloy's mechanical properties. The optimization of process temperature plays a vital role in managing the thermal profile and preventing undesirable consequences such as overheating or excessive cooling. These adverse effects can significantly impact the microstructure and properties of the alloy. The finer grain size of the FSPed samples resulted from the intense plastic deformation and dynamic recrystallization during the process. This grain refinement improved hardness, wear, and corrosion resistance. The temperature distribution during FSP using finite element simulation was highly dependent on the process parameters, such as the rotational speed and the dwell time. The results of this study are employed to develop a fitting model to predict the temperature distribution along the workpiece during the dwelling stage, which can be used to optimize the process parameters for different applications. The optimization of the heat generation inside the stirred zone plays a vital role in managing the thermal profile and preventing undesirable consequences such as overheating or excessive cooling. These adverse effects can significantly impact the microstructure and properties of the alloy. [ABSTRACT FROM AUTHOR]

This paper studies the effect of the laser melting process (LMP) on the microstructure and hardness of a new modified AlCuMgMn alloy with zirconium (Zr) and Yttrium (Y) elements. Homogenized (480 °C/8 h) alloys were laser-surface-treated at room temperature and a heating platform with in situ heating conditions was used in order to control the formed microstructure by decreasing the solidification rate in the laser-melted zone (LMZ). Modifying the AlCuMgMn alloy with 0.4 wt% Zr and 0.6 wt% Y led to a decrease in grain size by 25% with a uniform grain size distribution in the as-cast state due to the formation of Al3(Y, Zr). The homogenization dissolved the nonequilibrium intermetallic phases into the (Al) matrix and spheroidized and fragmentized the equilibrium phase's particles, which led to the solidification of the crack-free LM zone with a nonuniform grain structure. The microstructure in the LMZ was improved by using the in situ heating approach, which decreased the temperature gradient between the BM and the melt pool. Two different microstructures were observed: ultrafine grains at the boundaries of the melted pool due to the extremely high concentration of optimally sized Al3(Y, Zr) and fine equiaxed grains at the center of the LMZ. The combination of the presence of ZrY and applying a heating platform during the LMP increased the hardness of the LMZ by 1.14 times more than the hardness of the LMZ of the cast AlCuMgMn alloy. [ABSTRACT FROM AUTHOR]

The decrease of superplastic forming temperature and improvement of post-forming mechanical properties are important issues for titanium-based alloys. Ultrafine-grained and homogeneous microstructure are required to improve both processing and mechanical properties. This study focuses on the influence of 0.01–2 wt.% B (boron) on the microstructure and properties of Ti-4Al-3Mo-1V (wt.%) alloys. The microstructure evolution, superplasticity, and room temperature mechanical properties of boron-free and boron-modified alloys were investigated using light optical microscopy, scanning electron microscopy, electron backscatter diffraction, X-ray diffraction analysis, and uniaxial tensile tests. A trace addition of 0.01 to 0.1 wt.% B significantly refined prior β-grains and improved superplasticity. Alloys with minor B and B-free alloy exhibited similar superplastic elongations of 400–1000% in a temperature range of 700–875 °C and strain rate sensitivity coefficient m of 0.4–0.5. Along with this, a trace boron addition provided a stable flow and effectively reduced flow stress values, especially at low temperatures, that was explained by the acceleration of the recrystallization and globularization of the microstructure at the initial stage of superplastic deformation. Recrystallization-induced decrease in yield strength from 770 MPa to 680 MPa was observed with an increase in boron content from 0 to 0.1%. Post-forming heat treatment, including quenching and ageing, increased strength characteristics of the alloys with 0.01 and 0.1% boron by 90–140 MPa and insignificantly decreased ductility. Alloys with 1–2% B exhibited an opposite behavior. For the high-boron alloys, the refinement effect of the prior β-grains was not detected. A high fraction of borides of ~5–11% deteriorated the superplastic properties and drastically decreased ductility at room temperature. The alloy with 2% B demonstrated non-superplastic behavior and low level of strength properties; meanwhile, the alloy with 1% B exhibited superplasticity at 875 °C with elongation of ~500%, post-forming yield strength of 830 MPa, and ultimate tensile strength of 1020 MPa at room temperature. The differences between minor boron and high boron influence on the grain structure and properties were discussed and the mechanisms of the boron influence were suggested. [ABSTRACT FROM AUTHOR]

This work studies the effect of incorporating a mix of reinforcement particles of a hard and soft nature on the microstructure and mechanical and physical properties of a high-strength aluminum alloy, AA7075. A friction stir processing technique was used for compositing the surface of this alloy. The vanadium carbide (VC) was selected to be the hard reinforcement, while the boron nitride (BN) and graphene nanoplates (GNPs) were chosen as soft reinforcements. Mono VC, hybrid reinforcements combined of 50 vol.% VC and 50 vol.% BN, and triple reinforcements combined of 33.4 vol.% VC, 33.3 vol.% BN, and 33.3 vol.% GNPs were used for producing the composites. Intensive grain refinement was observed, 930%, in the composite with triple reinforcements. The microhardness and the ultimate compressive strength were improved and reached b0, 29%, respectively, in composites that contained GNPs. The thermal properties were significantly improved, and the coefficients of thermal expansion (CTE) and thermal conductivity decreased to 88% and 15%, respectively. The composite's electrical conductivity was decreased by 58% with triple reinforcements. [ABSTRACT FROM AUTHOR]

This study focused on the microstructural analysis, superplasticity, modeling of superplastic deformation behavior, and superplastic forming tests of the Al-Mg-Si-Cu-based alloy modified with Fe, Ni, Sc, and Zr. The effect of the thermomechanical treatment with various proportions of hot/cold rolling degrees on the secondary particle distribution and deformation behavior was studied. The increase in hot rolling degree increased the homogeneity of the particle distribution in the aluminum-based solid solution that improved superplastic properties, providing an elongation of ~470–500% at increased strain rates of (0.5–1) × 10−2 s−1. A constitutive model based on Arrhenius and Beckofen equations was used to describe and predict the superplastic flow behavior of the alloy studied. Model complex-shaped parts were processed by superplastic forming at two strain rates. The proposed strain rate of 1 × 10−2 s−1 provided a low thickness variation and a high quality of the experimental parts. The residual cavitation after superplastic forming was also large at the low strain rate of 2 × 10−3 s−1 and significantly smaller at 1 × 10−2 s−1. Coarse Al9FeNi particles did not stimulate the cavitation process and were effective to provide the superplasticity of alloys studied at high strain rates, whereas cavities were predominately observed near coarse Mg2Si particles, which act as nucleation places for cavities during superplastic deformation and forming. [ABSTRACT FROM AUTHOR]

The ceramic particle reinforcement process is one of the most utilized techniques to enhance the metal surface. The current investigation uses vanadium and niobium carbides to reinforce the AA6061 alloy using the friction stir process (FSP). The mechanical properties are evaluated using ultrasound and conventional compressive tests; furthermore, the microstructure and physical properties are carried out to show the effect of single and hybrid additives of ceramic particles on the surface composites of aluminum alloy. Scanning electron microscopy (SEM) is utilized to examine the presence and distribution of the reinforcement VC and NbC particles inside the composite matrix. The microstructure examination revealed a good dispersion and homogenized distribution of the reinforcement particles. The results indicated that reinforcement particles significantly enhanced the mechanical and physical properties. The VC and NbC particles play an important role in improving the surface hardening behavior and grain refinement by restricting grain growth during the dynamic recrystallization process in the FSP action. The hybrid composited AA6061/NbC + VC recorded an increase in the compressive stress, yield stress, and hardness of 25%, 20%, and 50%, respectively, relative to the base metal, in addition to a 55% decrease in the coefficient of the thermal expansion (CTE) was reported. Moreover, the hybrid composite AA6061/NbC + VC significantly affected the corrosion rate with a reduction of 45%. [ABSTRACT FROM AUTHOR]

Due to the engine's start/stop system and a sudden increase in speed or load, the development of alloys suitable for engine bearings requires excellent tribological properties and high mechanical properties. Including additional elements in the Al-rich matrix of these anti-friction alloys should strengthen their tribological properties. The novelty of this work is in constructing a suitable artificial neural network (ANN) architecture for highly accurate modeling and prediction of the mechanical properties of the bearing aluminum-based alloys and thus optimizing the chemical composition for high mechanical properties. In addition, the study points out the impact of soft and more solid phases on the mechanical properties of these alloys. For this purpose, a huge number of alloys (198 alloys) with different chemical compositions combined from Sn, Pb, Cu, Mg, Zn, Si, Ni, Bi, Ti, Mn, Fe, and Al) were cast, annealed, and tested for determining their mechanical properties. The annealed sample microstructure analysis revealed the formation of soft structural inclusions (Sn-rich, Sn-Pb, and Pb-Sn phases) and solid phase inclusions (strengthened phase, Al2Cu). The mechanical properties of ultimate tensile strength (σu), Brinell hardness (HB), and elongation to failure (δ) were used as control responses for constructing the ANN network. The constructed network was optimized by attempting different network architecture designs to reach minimal errors. Besides the excellent tribological characteristics of the designed set of alloys, soft inclusions based on Sn and Pb and solid-phase Cu inclusions fulfilled the necessary level of mechanical properties for anti-friction alloys; the maximum mechanical properties reached were: σu = 197 ± 7 MPa, HB = 77 ± 4, and δ = 20.3 ± 1.0%. The optimal ANN architecture with the lowest errors (correlation coefficient (R) = 0.94, root mean square error (RMSE) = 3.5, and average actual relative error (AARE) = 1.0%) had two hidden layers with 20 neurons. The model was validated by additional experiments, and the characteristics of the new alloys were accurately predicted with a low level of errors: R ≥ 0.97, RMSE = 1–2.65, and AARE ˂ 10%. [ABSTRACT FROM AUTHOR]

The paper studies the influence of 0.5–1.8 wt.% Ni alloying on the superplasticity, microstructural evolution, and dynamic grain growth effect in a temperature range of 625–775 °C and room temperature mechanical properties of two-phase Ti-Al-Mo-V alloys. Due to a decrease in β transus and an enhancement in the alloy diffusivity, an increase in Ni content significantly improved superplasticity. The Ni-modified alloys exhibited 1.5–3-fold lower flow stress, a 2.5–3-fold greater elongation to failure, and 1.4–1.7-fold higher strain rate sensitivity m coefficient compared to the Ni-free alloy. An intermetallic Ti2Ni compound precipitated in the 1.8 wt.% Ni-modified alloy during low-temperature deformation at 700 °C and decreased superplastic properties. The Ti-4Al-3Mo-1V-0.1B alloy with 0.9 wt.% Ni exhibited a good combination of the superplastic behavior and room-temperature mechanical properties: an elongation to failure of 500–900% at a low-temperature range of 625–775 °C and constant strain rate of 1 × 10−3 s−1 and a yield strength of 885 MPa and ultimate tensile strength of 1020 MPa after pre-straining for 100% in a superplastic regime and strengthening heat treatment. [ABSTRACT FROM AUTHOR]

The application of superplastic forming for complex components manufacturing is attractive for automotive and aircraft industries and has been of great interest in recent years. The current analytical modeling theories are far from perfect in this area, and the results deduced from it characterize the forming conditions insufficiently well; therefore, successful numerical modeling is essential. In this study, the superplastic behavior of the novel Al-Mg-Fe-Ni-Zr-Sc alloy with high-strain-rate superplasticity was modeled. An Arrhenius-type constitutive hyperbolic-sine equation model (ACE) and an artificial neural network (ANN) were developed. A comparative study between the constructed models was performed based on statistical errors. A cross validation approach was utilized to evaluate the predictability of the developed models. The results revealed that the ACE and ANN models demonstrated strong workability in predicting the investigated alloy's flow stress, whereas the ACE approach exhibited better predictability than the ANN. [ABSTRACT FROM AUTHOR]

In this study, two successive methods were used to improve the grain structure and the mechanical and physical properties of Al 5052 aluminum alloy. The modifying elements, 0.99 wt.% of titanium (Ti) and 0.2 wt.% of boron (B), were added during the casting process. After solidification, single- and double-pass friction stir processing (FSP) were performed to achieve additional grain refinement and disperse the newly formed phases well. The addition of Ti–B modifiers significantly improved the mechanical and physical properties of the Al 5052 aluminum alloy. Nevertheless, only a 3% improvement in microhardness was achieved. The ultimate strength (US), yield strength (YS), and elastic modulus were investigated. In addition, the electrical conductivity was reduced by 56% compared to the base alloys. The effects of grain refinement on thermal expansion and corrosion rate were studied; the modified alloy with Ti–B in the as-cast state showed lower dimension stability than the samples treated with the FSP method. The grain refinement significantly affected the corrosion resistance; for example, single and double FSP passes reduced the corrosion rate by 11.4 times and 19.2 times, respectively. The successive FSP passes, resulting in a non-porous structure, increased the bulk density and formed precipitates with high bulk density. [ABSTRACT FROM AUTHOR]

Improving the mechanical durability and wear resistance of aluminum alloys is a research challenge that can be solved by their reinforcement with ceramics. This article is concerned with the improvement of the mechanical properties and wear resistance of the AA2024 aluminum alloy surface. Surface composites were prepared by incorporating a hybrid of heavy particles (tantalum carbide (TaC), light nanoparticles, and boron nitride (BN)) into the AA2024 alloy using the friction stir process (FSP) approach. Three pattern holes were milled in the base metal to produce the composites with different volume fractions of the reinforcements. The effects of the FSP and the reinforcements on the microstructure, mechanical properties, and wear resistance are investigated. In addition to the FSP, the reinforced particles contributed to greater grain refinement. The rolled elongated grains became equiaxed ultrafine grains reaching 6 ± 1 µm. The refinement and acceptable distribution in the reinforcements significantly improved the hardness and wear resistance of the produced composites. Overall, the hardness was increased by 60% and the wear resistance increased by 40 times compared to the base alloy. [ABSTRACT FROM AUTHOR]

In the present work, an advanced technique was applied to coat an Al 2024 alloy with a surface composite layer reinforced with various nanoparticles. The surface of Al 2024 aluminum alloy was modified with Ta2C, Al2O3 and multi wall carbon nanotubes MWCNTs nanoparticles by friction stir process (FSP). An improvement in the surface of the fabricated nanocomposite due to the refinement of the microstructure grains was achieved. In addition, a significant improvement in the hardness and wear behavior was observed. The reinforcement particles were incorporated into double and triple hybrid composite particles to determine the most effective combination for the controlled properties. The results showed that for the composite reinforced with a double hybrid of Al2O3 and MWCNTs, the microstructure grains of the fabricated nanocomposite surface were refined by 40 times. The hardness was significantly improved, i.e., it was increased by 48% by incorporating the triple reinforcement (Ta2C, Al2O3, and MWCNTs) into the surface of Al 2024 aluminum alloy. The results of wear properties were in agreement with the results of hardness; the maximum wear resistance was obtained for Al 2024-Ta2C + Al2O3 + MWCNTs, and the wear rate was reduced by 11 times. [ABSTRACT FROM AUTHOR]

AlZnMgCu, the high-strength aluminum alloy, is unsuitable for laser melting applications due to its high hot cracking sensitivity and large solidification temperature range. Adapting this alloy for laser melting processing is a high-demand research issue for extending its use. Thus, this paper investigates the effect of adding 4%Si, 4%Si-Sc+Zr, 4%Si-Ti+B, and homogenization annealing on the laser melting process (LMP) of AlZnMgCu alloy. Homogenization annealing at 500 °C for 6.5 h was selected to dissolve most of the low melting temperature phases into the grain matrix and perform stable alloys for the LMP. The pulsed laser melting process (PLM) was performed on the as-casted and the homogenized samples. The microstructures of the as-casted, the homogenized alloys, and after the LMP were evaluated. In addition, the hardness of the base metal (BM) and laser melted zone (LMZ) were measured. The results revealed that the microstructure was enhanced and refined in the as-cast state by adding the modifiers due to the increasing nucleation potency of solidification sites and the formation of primary Al3(Ti, Zr, Sc) phases. The average grain size was decreased by 15.6 times when adding 4%Si + 0.4%Zr + 0.29%Sc, while it decreased by 10.2 times when adding 4%Si + 1%Ti + 0.2%B. The LMZ of the as-casted samples exhibited a non-uniform distribution of the grains and the elements after the LMP. This was attributed to the evaporation of Zn, Mg during the high laser power process besides the non-uniform distribution of elements and phases in samples during casting. After the laser treating of the homogenized samples with 4%Si-Sc + Zr, uniform columnar grains were formed in the direction of the laser. The presence of Ti and B changed the crystallization nature, resulting in the LMZ with very fine and equiaxed grains due to forming many nucleation centers during solidification. The hardness values have positively increased due to Si addition and adding a combination of Ti + B and Sc + Zr. The maximum hardness was 153.9 ± 5 HV achieved in the LMZ of the homogenized samples of 4%Si + 1%Ti + 0.2%B. [ABSTRACT FROM AUTHOR]

In this paper, AA5250 aluminum sheets are reinforced with boron nitride (BN), silicon carbide (SiC), aluminum oxide (Al2O3), and vanadium carbide (VC). The nanocomposites metal matrix are manufactured using friction stir processing (FSP). A novel analytical comparison based on an assessment of mechanical, physical properties and the cost of manufactured materials was conducted to help the engineers and designers choose the most economically feasible nanocomposite. The results revealed extra grain refining for all composites in the stirred zone (SZ) due to the Zener-pinning mechanism. The smallest grain size was obtained in AA5250/BN, and it decreased 20 times that of the base metal (BM). The highest wear resistance was achieved in AA5250/SiC, followed by AA5250/VC and AA5250/BN. The lowest coefficient of friction was obtained for AA5250/BN due to the self-lubrication property of BN; which was μ = 0.28. SiC AA5250 had the highest hardness, increasing three times more than the base metal in terms of its hardness. There was a detailed discussion of the probable explanations for the improvements. However, the outstanding characteristics of the BN nanoparticles, the AA5250/BN was reported to be lower than the AA5250/SiC. In comparison, the AA5250/SiC nanocomposite exhibits the optimum value due to its fitting for different properties relative to the cost. [ABSTRACT FROM AUTHOR]

Increasing the strain rate at superplastic forming is a challenging technical and economic task of aluminum forming manufacturing. New aluminum sheets exhibiting high strain rate superplasticity at strain rates above 0.01 s−1 are required. This study describes the microstructure and the superplasticity properties of a new high-strength Al-Zn-Mg-based alloy processed by a simple thermomechanical treatment including hot and cold rolling. The new alloy contains Ni to form Al3Ni coarse particles and minor additions of Zr (0.19 wt.%) and Sc (0.06 wt.%) to form nanoprecipitates of the L12-Al3 (Sc,Zr) phase. The design of chemical and phase compositions of the alloy provides superplasticity with an elongation of 600–800% in a strain rate range of 0.01 to 0.6/s and residual cavitation less than 2%. A mean elongation-to-failure of 400% is observed at an extremely high constant strain rate of 1 s−1. The strain-induced evolution of the grain and dislocation structures as well as the L12 precipitates at superplastic deformation is studied. The dynamic recrystallization at superplastic deformation is confirmed. The superplastic flow behavior of the proposed alloy is modeled via a mathematical Arrhenius-type constitutive model and an artificial neural network model. Both models exhibit good predictability at low and high strain rates of superplastic deformation. [ABSTRACT FROM AUTHOR]

The mechanical properties and microstructure of as-cast and homogenized AA7075 were investigated. This alloy was modified by adding transition elements 0.3%Sc + 0.5%Zr, 1%Ti + 0.2%B, and 1%Fe + 1%Ni for use in additive manufacturing applications. After adding Ti + B and Sc + Zr, the structure became uniform and finer with the formation of the Al3(Sc, Zr) and TiB2 phases. Coarse structures were obtained with the formation of an extremely unfavorable morphology, close to a needle-like structure when Fe + Ni was added. The mechanical properties of the modified alloys were increased compared to those of the standard alloy, where the best ultimate tensile strength (UTS) and yield strength (YS) were obtained in the AA7075-TiB alloy compared to the standard alloy in as-cast and homogenized conditions, and the highest hardness value was provided by Fe + Ni additives. The effect of the laser melting process on the microstructure and mechanical properties was investigated. Single laser melts were performed on these alloys using 330 V and a scanning speed of 8 mm/s. During the laser melting, the liquation of the alloying elements occurred due to non-equilibrium solidification. A change in the microstructures was observed within the melt zone and heat-affected zone (HAZ). The hardness of the laser-melted zone (LMZ) after adding the modification elements was increased in comparison with that of the standard alloy. Corrosion testing was performed using a solution of 100 mL distilled water, 3.1 g NaCl, and 1 mL HCl over 5, 10, and 30 min and 1 and 2 h. The corrosion resistance of the alloy modified with FeNi was low because of the non-uniform elemental distribution along the LMZ, but in the case of modification with ScZr and TiB, the corrosion resistance was better compared to that of the standard alloy. [ABSTRACT FROM AUTHOR]

Determining a desirable strain rate-temperature range for superplasticity and elongation-to-failure are critical concerns during the prediction of superplastic forming processes in α + β titanium-based alloys. This paper studies the superplastic deformation behaviour and related microstructural evolution of conventionally processed sheets of Ti-6Al-4V alloy in a strain rate range of 10–5–10–2 s–1 and a temperature range of 750–900 °C. Thermo-Calc calculation and microstructural analysis of the as-annealed samples were done in order to determine the α/β ratio and the grain size of the phases prior to the superplastic deformation. The strain rate ranges, which corresponds to the superplastic behaviour with strain rate sensitivity index m ˃ 0.3, are identified by step-by-step decreasing strain rate tests for various temperatures. Results of the uniaxial isothermal tensile tests at a constant strain rate range of 3 × 10−4–3 × 10−3 s−1 and a temperature range of 800–900 °C are presented and discussed. The experimental stress-strain data are utilized to construct constitutive models, with the purpose of predicting the flow stress behaviour of this alloy. The cross-validation approach is used to examine the predictability of the constructed models. The models exhibit excellent approximation and predictability of the flow behaviour of the studied alloy. Strain-induced changes in the grain structure are investigated by scanning electron microscopy and electron backscattered diffraction. Particular attention is paid to the comparison between the deformation behaviour and the microstructural evolution at 825 °C and 875 °C. Maximum elongation-to-failure of 635% and low residual cavitation were observed after a strain of 1.8 at 1 × 10−3 s−1 and 825 °C. This temperature provides 23 ± 4% β phase and a highly stable grain structure of both phases. The optimum deformation temperature obtained for the studied alloy is 825 °C, which is considered a comparatively low deformation temperature for the studied Ti-6Al-4V alloy. [ABSTRACT FROM AUTHOR]

The effect of isothermal multidirectional forging (IMF) on the microstructure evolution of a conventional Al–Mg-based alloy was studied in the strain range of 1.5 to 6.0, and in the temperature range of 200 to 500 °C. A mean grain size in the near-surface layer decreased with increasing cumulative strain after IMF at 400 °C and 500 °C; the grain structure was inhomogeneous, and consisted of coarse and fine recrystallized grains. There was no evidence of recrystallization when the micro-shear bands were observed after IMF at 200 and 300 °C. Thermomechanical treatment, including IMF followed by 50% cold rolling and annealing at 450 °C for 30 min, produced a homogeneous equiaxed grain structure with a mean grain size of 5 µm. As a result, the fine-grained sheets exhibited a yield strength and an elongation to failure 30% higher than that of the sheets processed with simple thermomechanical treatment. The IMF technique can be successfully used to produce fine-grained materials with improved mechanical properties. [ABSTRACT FROM AUTHOR]

This paper presents the effect of temperature and strain rate on the superplastic deformation behavior of Ti-3%Mo-1%V-4%Al, Ti-4%V-6%Al, and Ti-1.8%Mn-2.5%Al alloys, which have different initial microstructures. The microstructure, before and after superplastic deformation in the deformation regimes that provided the maximum elongation, was analyzed. The deformation regimes, corresponding to the minimum strain hardening/softening effect, provided a higher elongation to failure due to their low tendency toward dynamic grain growth. As the values of stress became steady (σs), the elongation to failure and strain-hardening coefficient were analyzed under various temperature–strain rate deformation regimes. The analysis of variance of these values was performed to determine the most influential control parameter. The results showed that the strain rate was a more significant parameter than the temperature, with respect to the σs, for the investigated alloys. The most influential parameter, with both the elongation to failure and strain-hardening coefficient, was the temperature of the Ti-3%Mo-1%V-4%Al and Ti-1.8%Mn-2.5%Al alloys and the strain rate of the Ti-4%V-6%Al alloy. [ABSTRACT FROM AUTHOR]

The effect of isothermal multidirectional forging (IMF) on the microstructure evolution of a conventional Al⁻Mg-based alloy was studied in the strain range of 1.5 to 6.0, and in the temperature range of 200 to 500 °C. A mean grain size in the near-surface layer decreased with increasing cumulative strain after IMF at 400 °C and 500 °C; the grain structure was inhomogeneous, and consisted of coarse and fine recrystallized grains. There was no evidence of recrystallization when the micro-shear bands were observed after IMF at 200 and 300 °C. Thermomechanical treatment, including IMF followed by 50% cold rolling and annealing at 450 °C for 30 min, produced a homogeneous equiaxed grain structure with a mean grain size of 5 µm. As a result, the fine-grained sheets exhibited a yield strength and an elongation to failure 30% higher than that of the sheets processed with simple thermomechanical treatment. The IMF technique can be successfully used to produce fine-grained materials with improved mechanical properties.