| 7075 aluminum alloy is a kind of high strength aluminum alloy widely used in aerospace and electronic industry.At present,T6 state 7075 aluminum alloy produced in domestic has poor corrosion performance and large residual stress.The existing research cannot provide perfect and comprehensive guidance for these problems.As an important step in the production of aluminum alloy,aging treatment can reduce stress,improve strength and enhance corrosion resistance,which has great potential in improving the performance of aluminum alloy.In this paper,aluminum alloys with different secondary aging temperature and regression temperature are obtained by controlling the aging process parameters.The mechanical properties,corrosion and residual stress are tested.The main conclusions are as follows :(1)After two-stage aging treatment,the elongation of 7075 aluminum alloy increases,but the strength and hardness decrease,and the softening effect is more obvious with the increase of two-stage aging temperature.The main strengthening phases of 7075 aluminum alloy are ηphase and η‘ phase,and η‘ phase begins to precipitate at about 150 °C.The alloy with two-stage aging has excellent corrosion resistance.When the temperature of two-stage aging is increased,the alloy shows better corrosion resistance.The recrystallization of the alloy occurs during the two-stage aging,the subgrains decrease,the large angle grain boundaries increase,and the internal stress decreases.(2)The hardness of 7075 aluminum alloy after regression treatment for about 50 min is relatively high.The strength of the alloy increases first and then decreases with the increase of regression temperature,and the elongation increases all the time.Regression reaging has effect on the grain orientation of aluminum alloy.After regression treatment at 170 °C,the contents ofη‘ and η phases precipitated in the alloy reach the maximum.The regression temperature determines the corrosion resistance of the alloy after regression reaging.Higher regression temperature lead to better corrosion resistance of the alloy,but the corrosion resistance of the aluminum alloy regression at 170 °C and 180 °C is close.Higher regression temperature lead to faster residual stress in the aluminum alloy decreases,and more substructures recrystallization occurs.Small angle grain boundaries are transformed into large angle grain boundaries,and the elastic strain energy in the grains is also reduced more completely.After comprehensive comparison of various properties,it is considered that 170 °C / 50 min is the optimal regression process for 7075 aluminum alloy.(3)The 7075 aluminum alloy with T6 state has higher strength and hardness.After two-stage aging treatment,the toughness of the alloy increases but the strength decreases.The alloy with regression re-aging has the strength of T6 state and the toughness of the alloy with two-stage aging treatment.There are more GP zone strengthening phases in T6 alloy,and moreη‘ phase and η phase are precipitated as strengthening phases after reaging treatment.The corrosion of T6 alloy is the most serious,and the corrosion resistance of 7075 aluminum alloy treated by regression re-aging is equivalent to that of two-stage aging,which is better than that of T6.The intragranular precipitates determines the strength and hardness of 7075 aluminum alloy,and has little relationship with substructure,recrystallization and grain boundary morphology.Regression reaging and two-stage aging can significantly reduce the residual stress of T6 state 7075 aluminum alloy.In this paper,the effects of three aging methods on the microstructure,corrosion resistance and residual stress of 7075 aluminum alloy were mainly studied.Based on the comprehensive performance,it was considered that the alloy after reaging at 120 °C/20 h+170 °C/50min+120 °C /16 h has good comprehensive performance.It provided experimental reference for the production and processing of enterprises. |
