Influence of Heat Treatment on Corrosion and Electrochemical Behaviour of Al-Mg-Si-Ag Alloys with Different Mg/Si

The influences of Mg/Si and heat-treatment on the corrosion performance of Al-Mg-Si-Ag alloy were studied. The results show that when the Mg/Si<1, apart from the precipitation of β phase, there is a small amount of elemental silicon. In the corrosion process, the Si element acts as a cathode, which on the one hand leads to the decrease of the corrosion potential, and on the other hand, it increases the corrosion rate. When Si is excessive, the βʺ density increases significantly, and the continuity of the grain boundary phase becomes higher, which promotes electrochemical corrosion, resulting in severe intergranular corrosion (IGC). In under-aging state, the alloy exhibits the best corrosion resistance. The corrosion current density in the slightly over-aged state is slightly lower than that in the peak-aged state. The slightly over-aging treatment can effectively improve corrosion resistance of the alloy. After the alloy treated by severely over-ageing, the grain boundary coarsened and result in the increase of corrosion current density.