Effects of Cu and age treatment on susceptibility to intergranular corrosion of Al-Mg-Si alloys

By the immersion corrosion tests and electrochemistry tests, the effects of changing Cu content and varying age treatments on the susceptibility to intergranular corrosion of Al-Mg-Si alloys have been studied. Phase structures of corrosion products were analyzed by XRD and the corrosion morphologies were observed by SEM. The results of immersion corrosion tests show that obvious intergranular corrosion is detected on the alloys with over 0.5% Cu and the maximum corrosion depth increases with increasing Cu content after the precipitation treatment. Slight intergranular corrosion is found on the alloys with over 1% Cu after the under-aged treatment. Pitting is observed on all alloys after the over-aged treatment. Results of electrochemistry tests indicate that φcorr varies to positive and Jcorr increases with increasing Cu content. The φcorr and Jcorr under the under-aged condition are more negative and smaller respectively than those under the precipitation-age condition.