Optimised composition and process design to develop sc-enhanced wrought al-si alloys

Abstract

In a number of aluminium (Al) alloys to date, scandium (Sc) additions have revealed a significant and beneficial effect on strengthening, even when added in small quantities. However, the strengthening response of the ternary Al-Si-Sc alloy system has been hampered by an apparent unfavourable interaction between silicon (Si) and Sc; forming the deleterious V-phase (AlSc2Si2) and thus limiting the allowable Si-content to ~0.15 wt.%. In this study, phase diagrams were calculated using CALPHAD and utilised to design Al-Si-Sc alloy compositions and heat treatment parameters. The Al-Si-Sc alloys were processed using a conventional route of wrought aluminium semi-products. A hardness improvement of up to 30% was achieved for the alloys containing Si as high as 0.8 wt.% in the F-temper. The improved hardness was mainly attributed to the homogeneously distributed, coherent, (Al,Si)3Sc nano-dispersoids in the α-Al matrix formed during a low temperature annealing treatment and retained in the F-temper condition.