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 (Mg-32(Al, Zn)(49)) and of stable eta (MgZn2) phase in Al7050 alloy. In addition, Sc microalloying element facilitates the precipitation of the eta' (MgZn2) hardening phase, while Ag microalloying element impedes the formation of the eta' (MgZn2) hardening phase. As a result, trace addition of Sc enhances the sigma(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%.