Effect of Sc and Zr additions on the microstructure/strength of Al-Cu binary alloys

Scandium increases the strength of aluminium alloys via three mechanism: 1) solid solution strengthening, 2) precipitation hardening, 3) grain structure control. Despite the well documented benefits, scandium has found very limited use in commercial grade aluminium alloys due to its high cost. However, new efficient extraction technologies promise an ensured supply of scandium and a significant drop in cost. Development of the next generation of aerospace Al alloys will come from innovation in alloy chemistry. One such innovation could be the addition of scandium in combination with Zirconium which increases the specific strength and stiffness of aluminium alloys through the precipitation of the L-12 Al-3(Sc, Zr) dispersoid. However, very little is known about the interactions of the Al-3(Sc, Zr) dispersoid and the theta'-phase. Here, the effects of Sc and Zr additions to a model Al-Cu alloy were examined. The precipitates were investigated through TEM and APT. EBSD was used to characterise the texture of the studied alloys. Finally, the ageing response of the alloys was monitored through tensile testing. The refinement of the Cu precipitates accounted for an increase of up to 120 MPa of the peak aged strength and the core/shell dispersoids accounted for up to 40 MPa.