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Ultrafine-grained (UFG) materials produced by severe plastic deformation methods generally exhibit a higher strength, but a lower uniform ductility. In this paper, an UFG Al–Zn–Mg–Cu alloy was fabricated via cross accumulative extrusion bonding (CAEB) and subsequent aging to achieve high strength and moderate uniform elongation. The influences of CAEB and subsequent aging on microstructure and tensile properties of the alloy were investigated. After CAEB, TEM characterization revealed that the microstructure exhibited typically ED-elongated ultrafine grains (740 ± 20 nm). Post-CAEB aging led to the formation of many nano-sized particles with different morphologies. These particles precipitated in the grain interiors and at grain boundaries, among which the main strengthening phase was η′ phase. EBSD characterization showed that the fraction of high angle grain boundaries increased to 61.0% for the post-CAEB aged alloy. At the same time, microtexture was significantly weakened as the CAEB process was applied to the alloy. The main texture components were mainly composed of Cu and S as well as a small amount of Brass and Cube. In addition, the tensile test at room temperature demonstrated that the post-CAEB aged sample possessed a high ultimate tensile strength of 562 MPa while simultaneously maintaining a moderate uniform elongation of 21.5%. • UFG Al–Zn–Mg–Cu alloy (740 ± 20 nm) was produced by cross accumulative extrusion bonding (CAEB). • Post-CAEB aging made the GP zone, η′ and η phase appear on the Al matrix. • The SST+CAEB+aging alloy possessed a high strength of 562 MPa and moderate uniform elongation of 21.5%. [ABSTRACT FROM AUTHOR]

To examine the effects of pre-induced precipitations on microstructure evolution and mechanical properties of pre-twinned ZK61 Mg alloy at elevated temperatures, the commercially rolled ZK61 Mg alloy sheets (AR samples) were pre-twinned and {10−12} tensile twins were added (PT samples). Some samples were aged, precipitated phases were introduced (PTA samples), and subsequently uniaxial tensile strain was applied. The results reveal that at elevated temperatures, the interactions of detwinning, dynamic recrystallization (DRX), and precipitation have a distinctive impact on the microstructure evolution. At room temperature (RT) and 100 ℃, strain is dominated by detwinning, while the precipitation phase impedes the detwinning behaviors. DRX influences the evolution of the microstructure at 150 ℃, 200 ℃, and 250 ℃. The presence of precipitated phases promotes recrystallization nucleation. Continuous DRX (CDRX), detwinning, and precipitated phase deformation are coordinated at 150 ℃. DRX in aged samples has a limited effect, while detwinning plays a dominant role. The ultimate tensile strength (UTS) value increment of PTA sample relative to PT sample reaches 31.8 MPa. The deformation is generated by the discontinuous DRX (DDRX) at 250 ℃, and the precipitation and DDRX have a higher impediment on detwinning, resulting in more twins restraining in the PTA sample. The UTS value of PTA sample only increases by 7.7 MPa compared with PT sample. • Precipitation effects detwinning and dynamic recrystallization in ZK61 Mg alloy. • Detwinning and recrystallization compete at elevated temperatures. • VPSC were used to analyze the slip behaviors. [ABSTRACT FROM AUTHOR]

In this study, accumulative extrusion bonding (AEB) was used to process Mg–1Gd/Mg–13Gd laminated composites, in which the Mg–13Gd layers had much finer grains than the Mg–1Gd layers. This grain size difference was maintained after 2-pass, but diminished after the 3-pass. The 2-pass composite samples exhibited an excellent combination of ultimate tensile strength (291 MPa), elongation (20.6%) and yield strength (144 MPa), which are much superior than the individual component materials. Moreover, the 2-pass samples also exhibited maximum extra strength and ductility that is higher than what is predicted by the rule-of-mixture. The observed high strength and ductility are mainly attributed to back-stress strengthening and work hardening, respectively. The 2-pass samples exhibited the highest back stress, indicating an optimum laminate thickness for producing the highest back stress hardening. This work provide a new understanding on the design of heterogeneous laminated Mg alloys for improving mechanical properties. [ABSTRACT FROM AUTHOR]

The special microstructure distribution of the friction stir welded (FSW) Mg alloys joints is usually responsible for the non-uniform deformation and poor mechanical properties. Hence, it was possible to improve the joint mechanical properties by modifying the microstructure. In the present study, two kinds of AM60/AZ31 Mg alloys dissimilar FSW joints with different microstructure were obtained using different rotation rates (800 rpm and 1600 rpm). The results of mechanical tests showed that the tensile strength and elongation of the joint at 1600 rpm were 13.5% and 115% higher than those at 800 rpm, respectively. The microstructure observation indicated that the grain size of various zones in the joint at 1600 rpm was obviously larger than that at 800 rpm, especially at the AM60 side. However, there was no obvious difference in the texture distribution of the two welds. In addition, microstructure observation after fracture showed that there were more twins in AM60 side of the joint with coarse grains. These coarse grains promoted the activation of basal slip and twinning in the regions far away from the nugget zone (NZ) interface. This weakened the strain localization of the joint to some extent. Meanwhile, the coarse grain joint had lower concentration degree of the strain and dislocation near the NZ boundary compared with the fine grain joint. These factors led to better mechanical properties of the joint with coarse grains. This work could provide some guidelines for improving the inhomogeneous deformation behavior of dissimilar Mg alloys FSW joints. [ABSTRACT FROM AUTHOR]