Combining pre-rolling with retrogression and re-aging treatment to balance strength and corrosion resistance of 7A99 Al alloy

The 7A99 Al alloy was subjected to peak aging (PA) and retrogression + re-aging (RRA), and the pre-rolling (R) was combined with RRA (RRRA) to balance the mechanical properties and corrosion resistance. The results show that the precipitates of PA-treated sample are mainly unstable eta' phase with small size, while the coarse and stable eta phase appears after RRA and RRRA. The grain boundary precipitates of PA-treated sample exhibit the smallest size and continuous distribution, while they show increased size, discontinuous distribution, and Cu enrichment after RRA and RRRA. The hardness and strength of RRRA-treated sample are higher than those of RRA-treated one, and they are even close to the values of PA-treated one. Moreover, the samples exhibit better corrosion resistance after RRA and RRRA than that after PA. These results indicate that the proposed RRRA method can enhance the corrosion resistance without a significant sacrifice on the mechanical strength.