Effect of grain boundary precipitation on corrosion of heating-aging treated Al-4.47Zn-2.13Mg-1.20Cu alloy

Abstract

To thoroughly explore the relationship between precipitation and corrosion in a precipitation-strengthened Al-4.47Zn-2.13Mg-1.20Cu (wt%) wrought alloy plate after a nonisothermal aging (NIA) treatment, specifically, a heating-aging treatment (HAT), electrochemical testing and transmission electron microscopy (TEM) were conducted in the present work. The H(5) process exhibited excellent corrosion resistance with a low corrosion current density (icorr) and a high corrosion potential (Ecorr) compared to those for the T6 treatment. After the HAT, the precipitates at the grain boundaries (GBs) gradually became intermittent with a narrow precipitate-free zone (PFZ), effectively preventing GBs precipitates from anodic dissolution. The HAT enabled the rapid diffusion and enrichment of Cu at the GBs and reduced the potential difference between the grain boundary and matrix, thereby decreasing the intergranular corrosion (IGC) susceptibility. Moreover, the time spent for a HAT can be decreased by approximately 70% in comparison with that for a T6 treatment. The current results indicate that NIAs could improve the mechanical properties and production efficiency with a decreased energy consumption.

Keywords

• Al–Zn–Mg–Cu wrought alloy
• Heating-aging treatment
• Intergranular corrosion
• Precipitation