High-strength dissimilar aluminum alloys are difficult to connect by fusion welding, while they can be successfully joined by friction stir welding (FSW). However, the asymmetrical deformation and heat input that occur during FSW result in the formation of a heterogeneous microstructure in their welded zone. In this work, the grain structure and texture evolution in the bottom zones of dissimilar FSW AA2024-T351 and AA7075-T651 joints at different welding speeds (feeding speeds) were quantitatively investigated. The results indicated that dynamic recrystallization occurs in the bottom zones of dissimilar FSW joints, and equiaxed grains with low grain sizes are formed at the welding speed of 60–240 mm/min. A high fraction of the recrystallized grains were generated in the bottom zones of the joints at a low welding speed, while a high fraction of the substructured grains are produced at a high welding speed. Different types of shear textures are produced in the bottom zones of the joints; the number fraction of shear texture types depends on different welding speeds. This study helps to understand the mechanism of microstructure homogenization in dissimilar FSW joints and provides a basis for further improving the microstructure of the welded zone for engineering applications.

This study investigates the influence mechanisms of temperature on the tensile properties of Mg-Zn-Ca alloys, with a focus on the activation differences of slip systems at room temperature (RT) and high temperature (HT), and their effects on work hardening behavior. Observations using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) reveal that Mg-Zn-Ca alloy deformation predominantly relies on basal slip and partial pyramidal slip at RT. The decomposition of pyramidal into basal dislocations enhance dislocation interactions, which increases the work hardening rate and tensile strength. In contrast, more non-basal and multi-slip systems are activated at HT, reducing dislocation interactions and leading to a decrease in the work hardening rate. The HT samples exhibit lower tensile strength but higher elongation. This study reveals the regulatory mechanism of pyramidal dislocation slip decomposition and dislocation interactions at different temperatures, providing a theoretical foundation for designing high-strength, high-ductility magnesium alloys.

Friction-stir-welded dissimilar AA2024/AA7075 joints have an apparent influence on grain and texture development at the weld interface due to differences in physical and chemical properties between the two aluminum alloys. In this work, the effect of tool shoulder profile on grain structure and texture evolution in the center interface zone (CIZ) and bottom interface zone (BIZ) of dissimilar AA2024/AA7075 joints were quantitatively studied by electron back-scattering diffraction (EBSD). The results indicate that abundant fine and coarse equiaxial grains are produced in the CIZ and BIZ of the joints produced with a concentric circle shoulder (CCS) and three-helix shoulder (THS), and the average grain size of the BIZ is lower than that of the CIZ for the same CCS or THS joint. A higher degree of recrystallization occurs in the CIZ of the joint with a CCS than that of the joint with a THS, while a similar degree of recrystallization is presented in the BIZ of the two joints. For the distribution of local misorientation angle between the two sides of the interface in the same CCS or THS joint, the CIZ manifests relatively uniform behavior, while the BIZ presents the characteristics of uneven distribution. Tool shoulder profile has a significant impact on the texture components at the weld interface, which results in different types of shear textures generated in the CIZ and BIZ of the two joints. It is beneficial to make out the microstructural evolution mechanism at the weld interface in dissimilar FSW joints for engineering applications in this study.

Two Ni-AlSi12 coatings were prepared using mechanical alloying (MA) and mechanical alloying followed by laser cladding (LC), respectively. Phase composition and microstructure variations caused by powder weight ratio and laser-specific energy were thoroughly analyzed in this study. Mechanical properties and oxidation behavior are markedly improved by subsequent laser cladding. The MA-LC coating, characterized by high densification and crack-free properties, presents a homogeneous microstructure with refined features. Microhardness testing reveals a marked superiority of the MA-LC coating over the conventional MA coating. The nano-hardness of MA-LC coating is 9.79 GPa, exhibiting that it is 6.84 times the nano-hardness of the MA sample. Owing to metallurgical bonding, the MA-LC coating possesses excellent scratch bonding performance. The MA-LC coating shows favorable oxidation behavior, due to the following three reasons: Firstly, oxygen diffusion can be effectively blocked by the compact Al₂O₃ oxide layer developed on the MA-LC coating surface, which reduces the oxidation velocity. Secondly, the coating’s mean grain dimensions demonstrate an increasing tendency after oxidation, which reduces the grain boundary serving as the oxygen diffusion channel. This enhancement significantly improves the coating’s oxidation resistance. Thirdly, analysis of the coating’s respective kernel average misorientation (KAM) map revealed a significant release of internal stress following 100 h oxidation, which can improve the coating’s resistance to spallation.

This study provides an in-depth investigation into the influence of yttrium (Y) addition on the ratcheting behavior of magnesium (Mg) alloys under asymmetric cyclic loading. Although pure Mg exhibits higher strength under quasi-static tension, the Mg–Y alloy demonstrates markedly superior resistance to ratcheting during cyclic deformation. The Mg–Y alloy shows a substantially reduced ratcheting strain accumulation rate accompanied by pronounced cyclic hardening, ultimately leading to a significant improvement in fatigue life. Transmission electron microscopy (TEM) reveals that the extensive activation of ⟨c + a⟩ dislocations and the resulting high dislocation density in the Mg–Y alloy play a pivotal role in promoting homogeneous plastic deformation and cyclic hardening, thereby effectively suppressing the accumulation of ratcheting strain. This work provides new insights for the development of high-performance, fatigue resistant Mg alloys.