Roles of Sc and Ag Microalloying Elements in the Mechanical Properties of Al-Zn-Mg-Cu (Al7xxx) Alloy

In this study, we use microstructural investigation to examine the effects of Sc and Ag microalloying elements on the mechanical properties of Al-Zn-Mg-Cu-based (7050) alloy. Macroscopically, Sc and Ag microalloying elements significantly reduce the formation of intermetallic particles of S (Al₂CuMg) and T (Mg₃₂(Al, Zn)₄₉) and of stable η (MgZn₂) phase in Al7050 alloy. In addition, Sc microalloying element facilitates the precipitation of the η’ (MgZn₂) hardening phase, while Ag microalloying element impedes the formation of the η’ (MgZn₂) hardening phase. As a result, trace addition of Sc enhances the σ_UTS value of the Al7050 alloy from 552 MPa to 594 MPa without lowering the elongation of the Al7050 alloy (15.0% → 15.5%). In contrast, the tensile strength of the Al7050 alloy decreases from 552 MPa to 456 MPa with the addition of Ag microalloying element, while the elongation increases from 15.0% to 21.0%.