EXFOLIATION CORROSION BEHAVIOR OF 7150 Al ALLOY

The exfoliation corrosion behavior of 7150 Al alloy after treatments of T6,T73 and RRA(with retrogression at 175℃)was investigated.The electrochemical behavior of a simulated η(MgZn2)precipitate in NaCl solution and the coupling behavior of the coupled system of η-phase and Al-matrix were examined.The corrosion morphology of a simulated Al alloy with η-phase particles was also observed.The results show that 7150-T6 Al alloy possesses great sensitivity to exfoliation corrosion,7150-T73 Al alloy has low susceptibility to exfoliation corrosion,which is close to that of 7150-RRA Al alloy with retrogression at 175℃ for 3 h.The corrosion potential of η precipitate in 7150 Al alloy is negative with respect to that of Al matrix,and its corrosion current density is greater.Therefore,the precipitate serves as anodic phase and anodic dissolution occurs on its surface.The precipitate is distributed continuously along the grain boundary of 7150-T6 Al alloy,and there exists an active corrosion path resulting from the galvanic action between precipitates and their adjacent Al matrix,resulting in its greatest sensitivity to intergranular corrosion and exfoliation corrosion.The precipitate of the T73 and RRA treated 7150 Al alloys is distributed discontinuously at the grain boundary,and their susceptibility to intergranular corrosion and exfoliation corrosion is greatly lowered.