Deformation microstructures, consisting of lattice defects such as dislocations, develop as a result of plastic deformation in metallic materials. Deformation microstructure is one of the most important factors determining the mechanical properties of metals. It has been found that the development of deformation microstructures is affected by crystal structure, crystal orientation, and stacking fault energy (SFE) on {1 1 1} plane in FCC metals and alloys. Huang et al. systematically investigated deformation microstructures in polycrystalline pure FCC metals (Al, Cu: SFE > 80 mJ/m²) and found that three different types of dislocation microstructures develop depending on the grain orientation. On the other hand, it has been reported that, in FCC alloys with low SFE (< 30 mJ/ m²), planar dislocation structures with dislocations constraint on their slip planes and deformation twins develop in grains of specific orientations. These microstructures are quite different from those of pure metals. However, it is still unclear how the transition of deformation microstructures and their dependence on crystal orientation occur with varying the SFEs in FCC metals and how they relate to the macroscopic mechanical properties. Therefore, this study aims to clarify the effects of crystal orientation and SFEs on room temperature deformation behaviour and evolution of deformation microstructures in FCC metals by systematically investigating the deformation microstructures in tensile-deformed Cu-Al alloys, in which the SFE can be easily controlled by changing the Al content. 

True stress-true strain curves and work hardening rate-true strain curves of Cu-1.0 at.%Al, Cu-3.0 at.%Al, and Cu-6.0 at.%Al (SFE ~ 60, 40, 30 mJ/m², respectively) were evaluated by tensile tests at room temperature. Uniform and total elongations were similar among these materials, while both flow stress and work hardening rate increased with increasing the Al concentration. The increase in the yield strength can be attributed to solid solution strengthening. Compared with Cu-1.0 at.%Al and Cu-3.0 at.%Al, the work hardening rate of Cu-6.0 at.%Al increased significantly after a true strain of about 0.05. This indicates that the deformation microstructures changed significantly at SFE of between 30 and 40 mJ/m². The effects of SFE on the deformation microstructures and mechanical properties in the alloys will be discussed in detail in the presentation by showing their microstructure images.