Effect of Rare Earth Sc Addition on Microstructure and Mechanical Properties of an Al-Cu-Mg-Ag Alloy

Al-5.3Cu-0.8Mg-0.6Ag alloys containing 0, 0.1, 0.3 and 0.5 (mass. %) Sc were prepared by ingot metallurgy and thermomechanical treatment. The effect of Sc addition on the precipitation and microstructure of the alloys has been investigated using mechanical testing, optical microscope, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been shown that trace Sc element refines the grains of the casting alloys and the average grain size decreases from 85 μm to 30 μm. Increasing Sc content from 0.1 to 0.3% accelerates the aging hardening process, increases the maximum hardness and the tensile strength of the extruded alloys from room temperature to 300 ℃. The high strength of the alloys with Sc is attributed to the high density and high thermal stability of fine Ω precipitates, and nanosized Al3(Sc,Zr) and AlCu(Zr, Sc) particles.