The precipitation strengthening of directionally solidified Al Si Cu alloys

The structure of directionally solidified (DS) eutectic alloys is generally composed of matrix and reinforcing phases which reveal a sharp fibre texture. The reinforcing phase of Al-Si alloys is built of a silicon-rich solid solution, embedded in the matrix of aluminium-rich solid solution. The growth direction of the both phases is near 〈200〉. The mechanical properties of pure Al-Si alloys are low and may be improved by the addition of another element like copper. The investigations were performed in an Al-Si hypoeutectic alloy with additions of 2 and 4 wt.% copper. The alloys were solution treated at 530 °C, quenched in water followed by ageing at 200 °C. The Al2Cu precipitates formed during ageing significantly increasing the mechanical properties of the investigated alloy. Hardness changes were measured in the course of ageing. The structure was investigated by means of scanning microscopy, X-ray phase analysis and lattice parameter measurements.