Phase transformations in isochronally annealed mould-cast and cold-rolled Al–Sc–Zr-based alloy

The effect of small additions of scandium and zirconium on microstructure, thermodynamic and mechanical properties during the non-isothermal annealing of the mould-cast and cold-rolled aluminium was studied. Electrical resistometry together with the microhardness (HV0.3) measurements and transmission electron microscopy compared to differential scanning calorimetry results were used to characterize the effect. The Al–Sc–Zr-based alloy with a small addition of Ti in both states reaches the peak hardness by annealing to 330 °C due to precipitation of the Al3Sc particles. Relative resistivity changes (above 240 °C) of both alloys exhibit similar dependence on annealing temperature. Precipitation of particles (L12 structure) at 390 °C and 450 °C was observed by TEM. The apparent activation energy for precipitation of Al3Sc particles was calculated. The decomposition sequence of oversaturated solid solution of the studied Al–Sc–Zr-based alloy is compatible with the recently published decomposition sequence of Al–Sc–Zr system and the formation of layer rich in Ti, namely: Sc-rich clusters → Al3Sc phase → layer rich in Zr → layer rich in Ti → Al3(Sc,Zr,Ti) phase.