Influence of Zr addition on the microstructure and properties of PM Al-8Fe-4Ni alloy

The microstructure and texture of PM Al-8Fe-4Ni and A1-8Fe-4Ni-2.5Zr (wt%) alloys were studied. All solute additions were retained in solid solution in the fine powder particles and only alpha-Al and tau (Al9FeNi) were present in the > 10 mu m size fractions inthe as atomised powders of both alloys. These phases were present in the as extruded and heat treated alloys at 673K with precipitation of L1(2)-Al3Zr occuring in the quaternary alloy after 1h at 673K. The as extruded rods consisted of a banded structure made of alternate fine and coarse microstructure in the extrusion direction and were characterised by a sharp [111] fiber texture component of the aluminium matrix in the ternary alloy. The quaternary alloy was significantly harder and exhibited a fairly random texture. Although coarsening of the tau phase was noted, the fact that the aluminium texture after heat treatment was similar to that of the as-extruded alloys indicates that the high level of dispersoids prevented significant grain growth or recrystallisation even after 1000h at 673K. The higher hardness and enhanced thermal stability of the quaternary alloy were attributed to the precipitation of L1(2)-Al3Zr. At 773K and 873K a sharp increase in the intensity of the fibre texture component occured with increasing time.