Size effects in aluminium alloy castings

A finding by Benzerga et al. (Acta Mater 2001; 49:3071) that the yield strength of Al–7Si–0.3Mg castings is smaller for castings with a fine secondary dendrite arm spacing (SDAS) than for those with a coarse SDAS is revisited. Previous experimental data for Al–Si–Mg castings are reviewed, and new experiments carried out, both on the original castings used in Benzerga et al. and on Al–Si binary alloy castings whose microstructures more closely conform to the theoretical model of Benzerga et al. The experimental results show that the inverse size effect reported by Benzerga et al. was a consequence of different heat-treatments applied to the original castings, rather than to any intrinsic size effect. The present results confirm that there is a negligibly small size effect in both heat-treatable (Al–Si–Mg) and non-heat-treatable (Al–Si) castings.