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A TD-tilted basal texture in Mg alloys often generates a strong planar mechanical anisotropy. Unfortunately, there has been not a quantitative study on this issue. In the present study, the mechanisms for the anisotropy of tensile yield strength in RD-TD plane were quantitatively studied for a Mg-2Zn-1Ca alloy with different grain sizes and textures. Here, RD and TD refer to the rolling direction and transverse direction of the plate. The results show that there is a strong planar yield anisotropy (∼ 24 ± 5 MPa), regardless of grain size, while this yield anisotropy is absent in texture with a circular distribution of basal poles. The examination of microstructure and X-ray diffraction analysis reveals that, besides basal slip as the predominant mode under both RD-tension and TD-tension, prismatic slip in RD-tension and both prismatic slip and extension twinning in TD-tension are also important. The parameters of Hall-Petch relation are also used to further analyze the mechanism for yield anisotropy. The changeable intercept, σ 0 , and invariant Hall-Petch slope, k, between RD-tension and TD-tension are rationalized accounting for this anisotropy. The reasons why there are different σ 0 and similar k between TD-tension and RD-tension are quantitively discussed. At last, a texture design for decreasing the planar yield anisotropy is given.

Friction stir welding (FSW) is an effective welding technique to realize the joining of dissimilar aluminum alloys. The microstructural heterogeneities induced by FSW across the joints could have curial implication for the corrosion performance of the joints. In this research, the microstructure and localized corrosion behavior of shoulder interface zone (SIZ), vortex zone (VZ), bottom zone (BZ) and bottom interface zone (BIZ) in the stir zone (SZ) of dissimilar FSW AA2024/AA7075 joint was systematically investigated through detailed microstructural characterization and relevant corrosion tests. The results indicated that plentiful of Cu-rich constituent particles are formed on AA2024 side and the areas near the interface on both sides, and corrosion originates from these regions. Grain size has little influence on corrosion behavior of the SZ, while the local regions with higher stored energy are more sensitive and liable to corrosion. The sequence of mixing degree of materials in the four regions of the SZ is: BZ > VZ > SIZ > BIZ, which is in contrast to the order of corrosion rate. Galvanic corrosion is detected in the SIZ and BIZ, and sufficient mixing of materials significantly weakens the galvanic corrosion, resulting in higher corrosion resistance in the BZ.

In this work, Mg–2Zn–0.5Ca (wt.%) alloy sheets fabricated according to various rolling parameters were evaluated to investigate the effect of rolling parameters on room-temperature stretch formability. The sheet rolled at 360 °C with a pass rolling reduction of 10~33% exhibited the worst I.E. value of 4.4 mm, while the sheet rolled at 360 °C with a pass rolling reduction of 20~50% exhibited the best index Erichsen (I.E.) value of 5.9 mm. Among the sheets, the (0002) basal texture intensity was the weakest, and the grain basal poles split away from the normal direction toward both the rolling direction and the transverse direction. Microstructural and deformation mechanism measurements of stretch forming to 2 mm for the sheet rolled at 360 °C with a pass rolling reduction of 20~50% by electron backscatter diffraction and in-grain misorientation axes showed that there was a higher activity of {10–12} extension twins and that a prismatic slip was initiated. As a result, the weakening of the texture and the broader distribution of basal poles in the plane contributed to the improved formability of the sheet rolled at 360 °C with a pass rolling reduction of 20~50%.

In this investigation, the local microstructure evolution, mechanical properties and corrosion behavior of the dissimilar friction stir welded AA2024/7075 joints were evaluated as a function of rotational speed. The results showed that the rotational speed mainly affects the local microstructure and performance of the dissimilar joints. Fine equiaxed grains are formed in the nugget zone (NZ). The average grain size decreases in the sequence of shoulder zone (SZ), center zone (CZ) and bottom zone (BZ), and increases with increasing rotational speed. Different types of shear textures are formed at different positions of the NZ, which vary with the rotational speed. The maximum tensile strength of 411.4 MPa is acquired in the joint at 950 rpm, with the welding efficiency of about 87.6 % relative to the AA2024 base material. The fracture position of all the joints is in the lowest hardness zone during tensile tests. Higher corrosion current density presents in the welded zone, which results from the formation of galvanic corrosion. The corrosion behavior of the welded zone is influenced by rotational speed and higher corrosion resistance can be acquired in the joint fabricated at 950 rpm due to the appropriate precipitates density and size.

In this work, we performed some joining experiments of dissimilar aluminum alloys AA2024-T351 and AA7075-T651 using friction stir welding (FSW) technique with different process parameters (rotational speed, welding speed and plunge depth). Response surface methodology based on a central composite rotatable design was used to establish the mathematical models predicting the tensile properties and corrosion rate of dissimilar FSW joints with some high confidence level. Analysis of variance method was employed to verify the developed models. Besides, the influences of FSW process parameters on tensile and corrosion properties of joints were analyzed. In order to obtain a desirable combination property of the dissimilar FSW joints, the optimum process parameters after experimental verification were proposed as: rotational speed 1495 rev/min, welding speed 187 mm/min and plunge depth 0.03 mm. This verification illustrated that the developed models are appropriate for the modeling and optimization of process.

In this work, the microstructure and texture evolution of an as-cast Mg-2Zn-2Gd alloy subjected to different hot rolling regimes (cross rolling (CR) and unidirectional rolling (UR), CR+UR and UR+UR, respectively) and subsequent annealing at 400 °C were systematically investigated. The hot CR helps to develop relatively homogeneous distribution of (0002) poles in a circle inclining about 40° away from the ND in the annealed sample. However, this type of texture cannot be retained after subsequent unidirectional rolling along the RD and annealing, forming a texture with (0002) poles inclining approximately 40° from the ND toward the TD. It is found that the (0002) poles of recrystallized grains generally distribute along the direction perpendicular to the rolling direction, irrespective of the orientations of parent grains. There is a intense in-plane anisotropy of yield strength in plates containing a TD-tilted texture, while the homogeneous distribution of (0002) poles along the TD and RD can completely remove this planar mechanical anisotropy.

In the present study, the texture evolution and mechanical anisotropy in a typical Mg–Zn–Ca alloy through hot cross rolling (CR) and unidirectional rolling (UR) were systematically studied. The results show that the rolling path greatly affects the annealed texture. The UR develops a texture with basal poles mainly distributing along the transverse direction (TD). By contrast, an ellipse-like (0002) texture with basal pole inclining largely away from the normal direction (ND) is developed after hot cross rolling and annealing. Therefore, the CR is an effective method to tailor the texture of the experimental alloy. Unfortunately, this ellipse-like texture could not reserve during the subsequent unidirectional hot rolling and annealing. Both UR and CR plates exhibit a strong planar mechanical anisotropy compared with the traditional unidirectional rolled plate. Keywords: Mg alloys, Hot cross rolling, Texture, Mechanical anisotropy

In the present research, the microstructure characterization of the thermo-mechanically affected zone (TMAZ) in dissimilar FSW AA2024/7075 joint was systematically investigated. The results showed that many Cu-rich and Zn-rich constituent particles are generated in the TMAZ on the advancing side (AS-TMAZ) and the retreating side (RS-TMAZ), respectively. This mainly depends on the corresponding base materials (BMs) at the AS and RS. The precipitated particles are coarsened in the AS-TMAZ and RS-TMAZ compared to the corresponding BMs owing to the thermal cycle produced during FSW. Grain bending occurs in the TMAZ, and the degree of grain curvature in the RS-TMAZ are more pronounced than that in the AS-TMAZ. Many dislocations and sub-grains including a large number of LAGBs can be found in the AS-TMAZ and RS-TMAZ. The entire texture intensity is stronger in the AS-TMAZ and weaker in the RS-TMAZ as compared to the corresponding BMs. The original texture components are changed and some new shear components can be produced as a result of the severe shear deformation during FSW. The hardness value of the AS-TMAZ and RS-TMAZ is lower than that of the corresponding BMs due to the precipitated particles coarsening during FSW.