Improving the intergranular corrosion resistance of Al-Mg-Si-Cu alloys without strength loss by a two-step aging treatment

In order to improve the intergranular corrosion (IGC) resistance of Al-Mg-Si-Cu alloys without strength loss compared to that of the T6 temper, a new two-step aging treatment has been developed in the present study. The two-step aging treatment includes pre-aging at a relatively higher temperature for a shorter time and then re-aging at a lower temperature for a relatively longer time. The microstructural observation shows that after the optimized two-step aging of 180 °C/2 h+160 °C/120 h, the microstructural characteristics of the alloy combines the matrix of high number density β″ precipitates and grain boundaries of discretely distributed GBPs. The type of microstructures is responsible for the improvement of IGC resistance of the alloy without strength loss.