Effect of Cooling Rate on Exfoliation Corrosion of Al-Zn-Mg-Cu Alloy Thick Plate

The effect of cooling rate on exfoliation corrosion of Al-Zn-Mg-Cu alloy thick plate was investigated by polarization curve test,corrosion immersion test and end quench method.The results show that with cooling rate deceasing,the resistance to exfoliation corrosion decreased,from EB to ED,the corrosion potential decreased,the corrosion current density increased,and the polarization resistance decreased.There is a linear relationship between polarization resistance and cooling rate.The decreasing of cooling rate results in the higher coverage ratio and lower copper content of the grain boundary precipitates,wider precipitate free zone near grain boundaries,which are the primarily responsible for lower resistance to exfoliation corrosion.