Effect of solute Si and Cu on grain size of aluminium alloys

The relationship between grain size and growth restriction factor (GRF) and solidification interval at hypoeutectic solute concentrations was investigated in Al-Si and Al-Cu binary alloys. Si and Cu both provide a grain refining effect for aluminium alloys that starts to deteriorate at approximately 3 wt-%Si and 5.7 wt-%Cu in Al-Si and Al-Cu binary alloys respectively. The GRF, which increases monotonically with increasing solute content until the eutectic point, cannot be correlated to grain size at high solute concentrations. The solidification interval, on the other hand, is inversely related with the measured grain size, producing a nearly perfect correlation for the entire range of hypoeutectic solute concentrations. The grain size decreases as long as the solidification interval increases and vice versa. The solidification interval impacts both the nucleation as well as the growth of alpha(Al) grains. A growing solidification interval facilitates increasing nucleation and growth restriction, favouring small grains.