Abstract
The influence of long term annealing at temperatures up to 773 K on microhardness and the microstructure of several melt spun Al-Zr-Ti alloys was studied. The microhardness stability depends on the content of Zr and Ti in these alloys. The best results were obtained in the Al-Al₃(Zr_0.5Ti_0.5) alloy where microhardness increases during annealing at 600 K with time up to 500 hours. The peak microhardness corresponds to the microstructure containing very small particles of the metastable L1₂ Al₃(Zr_xTi_1-x) phase formed by discontinuous precipitation. Over-aging occurring for longer annealing times at temperatures T ≥ 650 K is caused by the formation of much coarser particles of the stable Al₃(Zr_xTi_1-x) phase. The difference between the decomposition behaviour of supersaturated Zr-rich and Ti-rich Al-Zr-Ti alloys may be explained as a result of extremely different diffusion rates of Zr and Ti in Al at temperatures close to 600 K.

Key words
Al-based alloy for elevated temperatures, rapid solidification, microstructure, microhardness, TEM, elevated temperature stability

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