Preparation of Al-20Si-4.5Cu alloy and its composite from elemental powders

Hypereutectic Al-Si-Cu alloys with a low thermal expansion coefficient and good wear resistance are commonly prepared from pre-alloyed powders using atomization. In the present work, an attempt was made to explore the possibility of fabricating the materials from cheaper elemental powders through sintering the compacts of the mixture of a silicon powder and an Al-4.5Cu elemental powder in the liquid state. Another advantage of taking this fabrication route is that it gives an additional flexibility to incorporate Al2O3 particles into the alloys to form aluminium matrix composites with a further improved Young's modulus, dimensional stability and wear resistance. Due to the change in the phase constitution brought about by the silicon addition, the sintering scheme for the Al-Cu elemental powder must be modified. The results show that it is well possible to take advantage of the good sinterability of the Al-4.5Cu elemental powder, to maintain the dimensions of the Al-20Si-4.5Cu compacts and to hold their shape during liquid-phase sintering. After consolidation with hot extrusion and heat treatment, the materials show an improved Young's modulus and a lowered thermal expansion coefficient at the sacrifice of strength and ductility. The success in using the elemental powders to produce the hypereutectic Al-Si-Cu alloys and their composites opens up a new flexible and economic way to tailor the properties of the materials.