The Toughening Mechanism Of Ultra-Fine Grained Wrought Aluminium Alloy

The application of wrought aluminum alloys is restricted because of its low strength and low hardness. Ultra-fine grained/Nano-grain materials produced by severe plastic deformation technology (SPD) have high strength, but, they exhibit disappointingly low ductility. In this work, a wrought aluminum alloy sample was subjected to multi-directional forging (MF) and aging treatment. The strength of samples was enhanced by reducing grain-size after MF, and the ductility of ultrafine-grained (UFG) materials was improved due to the aging treatment. So the samples possess high strength and high ductility after the processing.In this thesis,2A80wrought aluminum alloy samples were subjected to MF and aging treatment. The hardness and stress-strain of samples were tested by hardness tester and stretch test machine. Microstructure features of the samples were characterized by metallographic microscope and transmission electron microscope (TEM). The evolution for Microscopic structure evolution and mechanical property were discussed in detail.The results show that the microstructure of samples were become UFG after the MF and aging treatment processing, the strength and the hardness were Increased significantly, also have a high plasticity. The hardness and the strength of the samples were subjected to MF at room temperature and aging treatment are up to116HBW and404.17MPa respectively, the tensile elongation is10.33%. Samples MF at the temperature of130℃and aging treatment are124HBW and387.09MPa respectively and the tensile elongation is10.60%.High strength and high hardness are duo to the grain-size be reduced in samples and a mass of dispersing precipitated phases are distribution in the matrix. At the same time, aging treatment made the UFG to a mixture structure of different grain size. The relatively coarse grain induced work hardening, which improve the ductility. Ultrafine particles distributing within the grains, which help to accumulate dislocations, increase the dislocation storage capability and resist dislocation slip, and then the ductility was also improved. The residual stress of the samples would relieve during the aging treatment, also enhance the ductility. A linear correlation strengthening mode of elastic-plastic was built on the engineering stress-strain curves. On this basis, the relationship between strength and plasticity of UFG materials were discussed in detail. These were providing fundamental insight into the mechanisms that govern the strength and ductility of UFG materials.