Preparation Of Ultrafine-Grained Wrought Aluminum Alloys With High Strength And High Ductile

The applications of wrought aluminum alloys are limited for their low strength, which leading to plastic deformation easily. In this work, a6061aluminum alloy was subjected to multi-directional forging (MF) and ageing treatment. An ultrafine-grained (UFG) sample with high strength and high ductility was formed in6061Al alloy by MF and ageing treatment. The MF process mainly contributes to strengthening and heat treatment to toughening.Microstructure features of the samples were characterized by optical microscope and transmission electron microscope. The mechanical properties were studied in comparison with coarse-grained sample. Fracture morphologies of samples were observed by scanning electron microscope.The microstructure observation shows that an UFG structure is formed after MF and aging treatment. The grain diameter is less than1μm and some coarse grains exist in the sample. Moreover, there are a mass of dispersing ultrafine second-phase particles well distributed in the grains.The results show that the strength increases and ductility decreases after MF processing. After performing MF process at room temperature and130℃, the tensile strength increases from275.9MPa to391.3MPa and341.9MPa, the elongation decreases from14.37%to9.27%and9.66%respectively. The strength and ductility improve simultaneously after post ageing treatment. After ageing treatment, the tensile strength increases to396.3MPa and386MPa, elongation increases to11.08%and11.02%respectively.The samples possess high strength and high ductility after MF and ageing treatment processing. The strength and hardness is enhanced markedly by grain refinement, high dislocation density and dispersing ultrafine second-phase particles within the grains. The ductility is improved due to reducing the forging stress, a mass of dispersing ultrafine second-phase particles within the grains, which increase work hardening. Mechanical properties of sample subjected to MF at room temperature and ageing are better than that performing MF at130℃and ageing. The fracture morphology of the tensile samples is characteristic of dimple, which indicates that the fractures belong to ductile fracture. The size and the number of the tensile fracture dimples decrease after MF process. After ageing treatment, the dimples size decrease but become uniform distribution and the number of dimples increase, which relate to a mass of dispersing ultrafine second-phase particles within Al matrix.