Effect of the Secondary Phase on the Corrosion of Al-Zn-Mg-Cu Alloy

A non-heat treatment way was applied to study the effect of the secondary phase on the corrosion of Al-Zn-Mg-Cu alloy in order to exclude the effect of variation of grain size. The area ration of corrosion pits and secondary phase (150 samples) was used to characterize the corrosion degree of secondary phase after Intergranular Corrosion test for a constant period. Then the effect of size and distribution of secondary phase was determined by using the SEMEDS and EPMA equipment, the Electrochemical test and the Image-pro plus software after immersion test. The results show that the corrosion resistance of Al-Zn-Mg-Cu alloys is positive related to the size of secondary phase. The sparse or dense phase distribution on and within grain boundary retard the pit initiate and extend along the grain boundary, so it increases the corrosion resistance of Al-Zn-Mg-Cu alloy.