EFFECT OF Cu CONTENT ON INTERGRANULAR CORROSION OF A NEW TYPE Al-Mg-Si ALLOY

The effect of Cu content and heat treatment condition on intergranular corrosion behavior of a new type Al-Mg-Si alloys,which is a candidate material for carrier-based aircraft,has been studied by immersion and electrochemical tests.The results of immersion test showed that the mode of corrosion changed from pitting corrosion to intergranular corrosion due to the addition of Cu into the alloy,the degree of corrosion became severe with increasing Cu content.Compared with the alloy under aged and over aged,the one treated according to T6 condition showed much strong susceptibility to intergranular corrosion,which was resulted from continuous distribution of precipitates along grain boundaries of the alloy at T6 status.The results of electrochemical test indicated that all the tested alloys may be passivated rapidly.The free corrosion potentials shifted to positive and the corrosion current densities of the alloys grew with increasing Cu content.The pitting potential,the critical potential for intergranular corrosion and the free corrosion potential shifted to negative with the increase of ageing time.The pitting potential and the free corrosion potential varied with aging time parabolically,however,the critical potential for intergranular corrosion linearly.