Effect of heat treatment on microstructure and properties of cast and deformed Al alloys with addition of Yb, Er and Zr

The response of isochronal and isothermal ageing on the microstructure, microhardness and electrical properties of as-cast and deformed AlYbEr and AlYbErZr alloys were studied. The addition of Zr does not affect the grain size of the alloys in the initial state. Stability of grain size in both AlYbEr and AlYbErZr as-cast alloys was proved up to ageing at 450 degrees C for 32 h. On the other hand recrystallized grains were already observed in cold rolled alloys after ageing at 450 degrees C for 2 h. It was found that Zr supports massive recrystallization of the alloys after ageing at 450 degrees C. The presence of L12-structured particles with dimensions about 20-100 nm was proved in the initial state of all studied aloys. Investigation of microstructure of the AlYbEr alloy after treatment up to 450 degrees C and 540 degrees C proved a presence of particles rich on Er, Yb, some of these pin dislocations. The structure of these particles could be tetragonal with the D019 or D023 lattice. In the AlYbErZr alloy many fine L12 particles (contain Er, Yb and Zr) were observed. The L12 particles were observed after ageing at 640 degrees C for 4 h in both alloys. The addition of Zr to the alloy highlighted the core-shell structure of these particles, moreover some of them have the double core-shell structure in the AlYbErZr alloy, where the outer shell contains Yb and Er, the inner shell contains Zr and Yb and Er was detected in the core.