Pitting corrosion of naturally aged AA 7075 aluminum alloys with bimodal grain size

The bimodal grain sized 7075 aluminum alloys with different ratios of coarse and fine grains were prepared and naturally aged for 300 d. The effects of grain size on pitting characteristics of alloys were investigated. Compared to those in fine grains, the intermetallic particles in coarse grains had bigger size, higher alloying elements content, larger area fraction and lower population density. With the increasing ratio of fine grains, the frequency of pitting current transients increased, while the lifetime and peak value of current transients decreased; the number and volume of stable pits on alloys also decreased considerably.