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The unique continuous extrusion-based severe plastic deformation approaches were proposed recently to process high-performance magnesium (Mg) alloys, while the in-depth deformation mechanisms under such complicated thermomechanical conditions were not well understood. In the present work, the fundamental deformation behaviors of AZ61 Mg alloy from 25 to 400 °C were firstly examined under uniaxial compression deformation. Then the deformation mechanisms and microstructural characteristics of AZ61 Mg alloy during continuous expansion extrusion forming (CEEF) were systematically investigated by microstructural observations, finite element and cellular automata simulations. The results showed that the continuous evolutions of temperature, larger strain level and complex stress state with strain rate range of 0 ∼ 5.98 s−1 during CEEF brought the distinctive dynamic recrystallization behaviors and texture development in AZ61 Mg alloy, which were different to that of uniaxial compression deformation. In details, a remarkable grain refinement was achieved via CEEF processing due to the simultaneous actions of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). Gradually enhanced CDRX were observed from center to edge region, which had significant effects on the texture distribution and texture strength. The c-axis of most grains rotated under distinctive shear strain following parabolic metal flow, resulting in stable fiber texture. In addition, the evolution of the internal texture of the alloy led to an obvious increase in the Schmid factor for the activation of basal 〈 c + a 〉 slip system. [ABSTRACT FROM AUTHOR]

SiC particle (SiCp) size has been found to significantly influence the hot workability of particle-reinforced aluminum matrix composites (AMC). In this work, therefore, three types of SiCp/6013 composites with different SiCp sizes (0.7, 5 and 15 μm) were prepared and then subjected to isothermal hot compression tests. In addition, constitutive analysis, processing maps and microstructural characterizations were used to reveal the influence of SiCp size on the hot workability of SiCp/6013 composite. The results showed that the values of hot deformation activation energy Q increased with decreasing SiCp size. Specifically, at lower temperatures (e.g., 350 and 400 °C), the highest peak stress was shown in the AMC with SiCp size of 0.7 μm (AMC-0.7), while in the AMC with SiCp size of 5 μm (AMC-5) at higher temperatures (e.g., 450 and 500 °C). This is because a finer SiCp size would lead to stronger dislocation pinning and grain refinement strengthening effects, and such effects would be weakened at higher temperatures. Further, dynamic softening mechanisms were found to transform from dynamic recovery to dynamic recrystallization with increasing SiCp size, and the dynamic recrystallization occurred more easily at higher temperatures and lower strain rates. Consequently, the instability zones of the composites are all mainly located in the deformation region with lower temperature and higher strain rate, and smaller SiCp results in larger instability zones. [ABSTRACT FROM AUTHOR]

The size and distribution of ceramic particles in aluminum matrix composites have been reported to remarkably influence their properties. For a single ceramic particle, the particle size is too small and prone to agglomeration, which makes the mechanical properties of the composites worse. When the ceramic particle size is too large, the particles and alloy at the interface are not firmly bonded, and the effect of dispersion distribution is not achieved, which will also reduce the mechanical properties of the composites. The multi-size ceramic particles are expected to improve this situation, while their effect on hot workability is less studied. In this study, the hot deformation behavior, constitutive model, processing map and SEM microstructure were investigated to evaluate the hot workability of multi-size SiC particle-reinforced 6013 aluminum matrix composites. The results showed that the increased deformation temperature and decreased strain rate could decrease flow stresses. The flow stress behaviors of the composites can be described by the sine-hyperbolic Arrhenius equation with the deformation activation energy of Q = 205.863 kJ/mol. The constitutive equation of the composites is ε   ˙ = 3.11592 × 10 13 sinh 0.024909 σ 4.12413 exp − 205863 R T . Then, the hot processing map of the SiCp/6013 composites was constructed and verified by SEM observations. The rheological instability zone was in the region of a high strain rate. The optimal processing zone for composites was 450~500 °C and 0.03~0.25 s−1. In addition, the strain level was found to increase both the Q value and the area of the instability zone. [ABSTRACT FROM AUTHOR]

High-temperature compression testing of powder metallurgy (PM) 8009Al alloy reinforced with 15 vol% Al 2 O 3 particles was performed at temperatures of 400–550 °C and strain rates of 0.001–1 s −1 . Its constitutive behavior and processing maps were investigated, and the related microstructural evolutions were characterized by scanning and transmission electron microscopy. The results showed that the stress peak decreased with increasing deformation temperature and decreasing strain rate, which could be described by the Zener-Hollomon parameter Z of the hyperbolic sine relation. The processing map constructed at a strain of 0.5 exhibited two safe processing domains: 500–530 °C at 0.001–0.003 s −1 and 530–550 °C at 0.001–0.01 s −1 . After taking into account the processing map, efficiency of power dissipation and microstructural observations, the optimum processing domain corresponding to 530–550 °C/0.001–0.01 s −1 was determined. As increasing deformation temperature and decreasing strain rate, the composite substructures with high density of dislocations were transformed into subgrains with distinct shapes and the fine dispersed Al 12 (Fe,V) 3 Si phase coarsened inside the matrix, which exhibited typical dynamic recovery (DRV) characteristics. In addition, the interaction of the dislocation-dispersed phase-Al 2 O 3 particle and its effect on the hot deformation behavior of the 8009Al/Al 2 O 3 composite were discussed. [ABSTRACT FROM AUTHOR]

Zn content has significant influence on the hot workability and final properties of Al–Zn–Mg–Cu alloys. In the present work, single and double stage hot compression tests have been performed on Al–Zn–Mg–Cu alloys with various Zn contents at temperatures of 300 °C and 400 °C, and strain rates of 0.01 s−1 and 0.1 s−1, respectively. The results showed that the static softening curve plateau was observed, both the duration of static softening plateau and softening fraction decreased with increasing Zn content at deformation temperature of 300 °C. When deformation temperature increased to 400 °C, the static softening curves appeared approximate typical sigmoidal shape with slight influence from Zn content. By combining additional in-situ electrical resistivity measurement, hardness testing and microstructural observations, the static softening mechanisms were found to be the functions of static recovery and precipitates coarsening at lower temperature, and static recovery and static recrystallization at higher temperature. The increased Zn addition mainly affected static softening mechanisms at 300 °C by forming precipitates. The simplified static softening kinetics were also investigated based on Johnson-Mehl-Avrami-Kolmogorov model which coupling static recovery and static recrystallization. • Single and double stage hot compression tests were performed on Al–Zn–Mg–Cu alloys with different Zn contents. • The duration of observed static softening plateau and softening fraction decreased with increasing Zn content at 300 °C. • The static softening curves appeared approximate typical sigmoidal shape with slight influence from Zn content at 400 °C. • The static softening mechanisms were SRV and precipitates coarsening at 300 °C, and SRV and SRX at 400 °C. • The simplified static softening kinetics were developed based on JMAK model which coupling SRV and SRX. [ABSTRACT FROM AUTHOR]

We experimentally investigated microstructure evolution and strengthening behaviors of three cold-worked austenitic steels that deform via dislocations, twinning and stacking faults. The development of stacking faults and twins acting as kinematical barriers for dislocation motion was found to be influenced by stacking fault energy and accumulated dislocations simultaneously, which in turn accelerate dislocation storage rate, strengthen the alloys, and develop high strain hardening rate. We thus proposed a nonadditive strengthening equation to rationalize experimental observation by combining the dislocation-based two-internal-variable model coupled with kinematical barriers. [Display omitted] [ABSTRACT FROM AUTHOR]

Increasing Zn content in Al–Zn–Mg–Cu alloys can improve the strength but reduce the ductility. Hot deformation is usually employed to process ultra-high strength Al–Zn–Mg–Cu alloys with high Zn addition to address the limitation of low workability. In the present work, uniaxial hot compression tests have been performed on Al–Zn–Mg–Cu alloys with different Zn contents at deformation temperatures of 300 °C and 400 °C, and strain rates of 0.01 s−1 and 0.1 s−1 respectively to study the influence of Zn content on dynamic softening. The results showed that with the increase of Zn content, the work hardening rate of Al–Zn–Mg–Cu alloys during the early stage of deformation was accelerated. And the peak stress and hot deformation activation energy increased first and then decreased slightly. Under deformation condition with high Z value, the dynamic softening of Al–Zn–Mg–Cu alloys increased gradually because that the increased Zn content accelerated the process of dynamic precipitation which was mainly responsible for the dynamic softening. While at low Z value, dynamic softening decreased with increasing Zn content when dynamic recovery and dynamic recrystallization were the predominant softening mechanisms. The addition of Zn inhibited the progress of dynamic recovery and dynamic recrystallization resulting and then decelerated dynamic softening. • The work hardening behavior of Al–Zn–Mg–Cu alloys increased with increasing Zn content. • The dynamic softening behavior of Al–Zn–Mg–Cu alloys was accelerated by the increased Zn content at 300 °C. • With the increase of Zn content, the dynamic softening of Al–Zn–Mg–Cu decreased at 400 °C. • The dynamic softening mechanisms were DPN at 300 °C, and DRV and DRX at 400 °C. [ABSTRACT FROM AUTHOR]