Effects of silicon content on microstructure and stress corrosion cracking resistance of 7050 aluminum alloy

Evolution of microstructure and stress corrosion cracking (SCC) susceptibility of 7050 aluminum alloy with 0.094%, 0.134% and 0.261% Si (mass fraction) in T7651 condition have been investigated. The results show that the area fraction of Mg2Si increases from 0.16% to 1.48% and the size becomes coarser, while the area fraction of the other coarse phases including Al2CuMg, Mg(Al, Cu, Zn)(2) and Al7Cu2Fe decreases from 2.42% to 0.78% with Si content increasing from 0.094% to 0.261%. The tensile strength and elongation of 7050-T7651 alloys is decreased with the increase of Si content by slow strain rate test (SSRT) in ambient air. However, electrical conductivity is improved and SCC susceptibility is reduced with the increase of Si content by SSRT in corrosion environment with 3.5% NaCl solution.