Effect of retrogression heating rate on the microstructure and corrosion resistance of aluminum alloy 7050

The effect of retrogression heating rate(340,57,and 4.3℃·min^-1) on the microstructure,intergranular corrosion and stress corrosion resistance of aluminum alloy 7050 was investigated using electrical conductivity,intergranular corrosion and stress corrosion cracking testing and transmission electron microscopy(TEM).The results show that retrogression heating rate affects significantly the corrosion resistance of the alloy treated by retrogression and reaging process,and that under the condition of considering the comprehensive mechanical properties,the alloy has a better corrosion resistance at the medium rate.After retrogression and reaging at the retrogression heating rate of 57℃·min^-1,the maximum intergranular corrosion depth of the alloy is 50 μm,i.e.Grade 3,which is shallower than those at the retrogression heating rates of 340℃·min^-1 and 4.3℃·min^-1.It is found that there are wider precipitate free zones and coarser discontinuous precipitates at grain boundaries.