Effects of Sc Addition and Retrogression and Re-aging on Microstructure and Mechanical Properties of Al-8Zn-2Mg-2Cu-0.15Zr Alloy

The synergistic effects of 0-0.3 wt.% Sc addition and retrogression and re-aging (RRA) on microstructure and mechanical properties were evaluated in Al-8.0Zn-2Mg-2Cu-0.15Zr alloy. The minor Sc addition can effectively refine the grains of the tested alloy. When the Sc content increased from 0 to 0.2 wt.%, the grain size decreased from 200-250 to 30 μm. As the Sc content increased from 0.2 to 0.3 wt.%, the grain size was still 30 μm, almost without change. The grain refining is due to the formation of Al 3 (Sc, Zr), which has a better coherent relationship with the matrix than Al 3 Zr. The RRA treatment results in a slight decrease in the tensile strength (R m ) and significant improvement in the total elongation (A) of the tested alloy. The sample's R m before and after the RRA decreased slightly from 517 to 510 MPa when the Sc is 0.3 wt.%; the A increased significantly from 6.0 to 12.0%. The tested alloy prepared by adding 0.1-0.3 wt.% Sc has a higher tensile strength and toughness than those alloys without Sc due to the formation of Al 3 (Sc, Zr). After the RRA treatment, both the formation of η (MgZn 2 ) and the release of internal stress decrease the strength and increase the total elongation of the tested alloy relative to values before the RRA treatment.