Effect of Sc micro-alloying on microstructure and corrosion behavior of 7085 alloy friction stir welded joints

Abstract

The corrosion resistance of 7085 and 7085Sc alloys FSW joints was studied by discussing intermetallic compounds, surface oxide film and grain boundary. It shows that Sc-containing Cu-rich phase and Al3(Sc,Zr) would form in 7085Sc alloy, which reduces the size of pitting sources, and is conducive to inhibiting the micro-galvanic corrosion of intermetallic compounds. Secondly, Sc element can promote the formation of a more stable oxide film on the surface, thereby reducing the corrosion rate of 7085Sc alloy. After FSW of the two alloys, the HAZ region produces a Cu-poor zone between GBPs and adjacent matrix due to the coarsening of grain boundary precipitates, which increases the micro-galvanic corrosion effect and easily leads to strong intergranular corrosion behavior. The intergranular corrosion of WNZ is mainly caused by the potential difference between GBPs and the matrix in the grains. The corrosion potential of each micro area of 7085Sc alloy welded joint is improved, and the corrosion resistance is more excellent. This is mainly due to the high proportion of low angle grain boundaries in each region, the decrease of Cu element difference on HAZ grain boundaries, and the decrease of potential difference between GBPs and intragranular in WNZ.