| Al-Zn-Mg-Cu alloy is a new generation of high-quality structural material with low density,high strength,good toughness,good diffusion performances and thermal processing performances,excellent welding performances,which is considered to be the most alternative non-ferrous metal material to replace steel and iron.7A60 aluminum alloy is a new type 7 series Al-Zn-Mg-Cu alloy developed by Beijing aviation materials research institute,it belong to high zinc-aluminium alloy.In this paper,the Al-Zn-Mg-Cu alloy was subjected to high pressure torsion experiment under different process parameters(such as deformation temperature and numbers of torsion)by the limited-type High Pressure Torsion die,and then proceed aging and solid solution aging experiments.According to the characteristics of Al-Zn-Mg-Cu alloy,using a series of modern material characterization techniques and related quantitative calculation theories,the microstructures,sub-structures(microstrain and dislocation density)and mechanical properties of samples deformed by HPT and samples deformed by HPT after heat treatment were studied extensively.The results shows that the grain size of 7A60 aluminum alloy was coarsen and the hardness is 84.5HV.High Pressure Torsion has important effect on microstructure of 7A60 alloy obviously,the grain is obviously refined to submicron level,the dislocation density increased significantly and the secondary phase of the alloy was broken,refined and dissolve into the matrix,the dissolve degree increased with the increase of temperature and deformation.The hardness of the alloy increased significantly,reaches to 124 HV after High Pressure Torsion.During the aging at 100 ?,the hardness of the alloy first increases and then decreases,the time reach to the peak which decreases with the increase of the dissolution degree of the secondary phase during High Pressure Torsion.During the aging at 135 ?,the alloy hardness first decreases and then increase to the level of Pre-aging level.The dislocation density of the alloy decreases significantly,the secondary phase first aggregated chain-like distribution and the size increases.As the aging time increases,the secondary phase dispersedly distrbuted and the size decreases.During the solution and aging,the hardness of the alloy first increases and then decreases,reaches to the maximum value after solid solution for 1 h and aging for 12 h.The secondary phase's size of the alloy is refined to sub-micronscale or nanoscale andmainly distributed along the grain boundary.The results show that the effect of refine grain strengthening is small and the secondary phase strengthening plays a major role in the heat treatment of 7A60 aluminum alloy deformed by High Pressure Torsion.The morphology,size,distribution of the secondary phase and interaction with dislocations of the secondary phase are the two main factors to affect the secondary phase strengthening.On the other hand,High Pressure Torsion accelerates the secondary phase of the alloy dissolved into the matrix,resulting in large number of defects(vacancies,grain boundaries and dislocations,etc.),which facilitates atom diffusion and shortens the optimal time of solid solution and aging of the alloy deformed by High Pressure Torsion.In addition,the mechanical properties of 7A60 alloy deformed by High Pressure Torsion after solid solution and aging treatment were tested at room temperature.The effect of High Pressure Torsion and heat treatment on the tensile strength and elongation of 7A60 aluminum alloy was studied.The results show that the tensile strength of 7A60 alloy increases significant after High Pressure Torsion and heat treatment compared with as-cast 7A60 alloy under T6,and the highest tensile strength reaches to 864 Mpa,increasing to 20%.The ductility of materials has also been improved,reaching a maximum to 17.2%.The combination of High Pressure Torsion and heat treatment not only enhances the tensile strength,but also improves the plasticity of the alloy. |
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