Effect of scandium addition on mechanical properties and corrosion resistance of medium strength Al-Zn-Mg(-Cu) alloy

Al-Zn-Mg alloys are widely used construct material for wide range of application including automotive industry, building, and aviation. Scandium is rare earth metal, which modifies structure of semi-products and can lead to increasing of tensile and yield strength because of Al3Sc intermetallics of nanoscale size. This paper describes results of influence of small addition of scandium (0,08 wt. %) on mechanical and corrosion properties of cold-rolled sheets of 1913 alloy. 1913 is Russian medium strength corrosion resistant weldable Al-Zn-Mg alloy with addition of Cu for improvement of stress corrosion resistance and Mn with Zr for structure improvement. It is shown that addition of Sc transforms kinetics of artificial aging and accelerates decomposition of solid solution, besides tensile strength increases up to 50 MPa in artificially aged tempers. Changes in microstructure and quench sensitivity are described; results of intergranural corrosion, exfoliation and stress corrosion tests are introduced after different heat treatment including peak strength aging and overaging tempers.