EFFECT OF Zn ADDITION ON INTERGRANULAR CORROSION RESISTANCE OF Al-Mg-Si-Cu ALLOYS

摘要

The under-paint film corrosion phenomenon and its prevention method for the 6000 series aluminum alloy sheet have been investigated. Cu-containing Al-Mg-Si alloys were susceptible to intergranular corrosion and the corrosion rate significantly increased under the film. The mechanism of the intergranular corrosion was the selective dissolution of the Mg_2Si phase that precipitated in the grain boundaries. Also the phenomenon was galvanically induced between less noble Mg_2Si and the noble Cu-containing grain body. A small amount of Zn addition was markedly effective to prevent intergranular corrosion and, therefore, improve the corrosion resistance of a painted sheet.