Effect Of Non-isothermal Regression And Re-ageing On Microstructure And Properties Of 7055 Aluminum Alloy

The 7055-T77 state aluminum alloy plate used in China~'s"big plane"project required high strength and good corrosion resistance.The monopoly of T77 technology from foreign countries and the difficulty of the aging degree controlling caused by non-isothermal phenomena during the plate aging process have become the bottleneck for the stable manufacture of high performance 7055-T77 state aluminum alloy thick plates.Therefore,it is of great significance to develop the retrogression and re-ageing of 7055 aluminum alloy thick plates under non-isothermal conditions with China's independent intellectual property rights.In this paper,hardness,electrical conductivity,room temperature tensile,exfoliation corrosion test,differential scanning thermal analysis and transmission electron microscopy were used to study the influence of pre-aging degree,regression heating rate and T_A(the highest regression temperature)on the microstructure and properties of 7055 aluminum alloy.The main conclusions are as follows:(1)Non-isothermal regression and re-aging process,have lower requirements on the accuracy of pre-ageing control,which is beneficial to engineering applications.(2)Regression heating rate and T_A(the highest regression temperature)have a great influence on the properties of the alloy.At the slow regression heating rate(1°C/min),the T_A temperature of the standard process is 215°C;and the T_A temperature of the standard process at the fast regression heating rate(3°C/min)is 225°C.(3)During furnace cooling regression the precipitation of fine precipitates in the crystals has a good strengthening effect,therefore,the hardness of the alloys increases.However,the grain boundary precipitates coarsely and the discontinuousness deepens,which is beneficial to the improvement of the corrosion resistance of the alloy..(4)Re-aging can increase the electrical conductivity of the alloy,but it has different effects on the hardness of the alloy under different regression heating rates.At the slow regression heating rate(1°C/min),the hardness of the alloy decreases after re-aging;while at the fast regression heating rate(3°C/min),the hardness of the alloy increases after re-aging.(5)The optimized non-isothermal regression and re-aging technology can make the alloy loss less strength but own high corrosion resistance.After pre-aging treated at 105°C,24h,heating at 3°C/min to 225°C and furnace cooling to room treatment,then re-aging treatment at 120°C,24h,the tensile strength and exfoliation corrosion grade of the alloy were 616.4 MPa and EA,respectively.The mechanical properties is near to the T6 state and the corrosion resistance is near to the T73 state.Besides,the aging process,which includes slow regression temperature-rising condition,is benifit to the heat treatment of thick plate under industrial conditions.