Microstructure and hardness of nanostructured Al–Fe–Cr–Ti alloys through mechanical alloying

This study investigates the microstructural and compositional evolution of Al93Fe3Ti2Cr2 alloys prepared via mechanical alloying (MA) starting from elemental powders. The potential of the MA-processed Al93Fe3Ti2Cr2 alloy for structural applications at both ambient and elevated temperatures has also been studied. It is found that the nanocrystallization process of the Al alloy proceeds via an initial increase followed by a subsequent decrease in dislocation density to form nano-grains with a dislocation-free interior. The difficulty with which to form supersaturated Al-based solid solutions depends on alloying elements with Fe being the easiest element and Cr the most difficult one to form supersaturated Al-based solid solutions. The hardness of MA-processed Al93Fe3Ti2Cr2 alloys at the as-milled condition can be twice that of 6061-Al alloys and higher than that of the cold drawn 1045 steel. The enhanced strengthening is attributed to grain refinement, formation of supersaturated solid solutions, and work hardening due to ball milling. After exposure to high temperatures (up to 450 °C) the MA-processed Al93Fe3Ti2Cr2 alloy still possesses superior room-temperature hardness due to strengthening of intermetallic precipitation and the retention of fcc-Al nano-grains.