Effect of Al₂O₃ addition on characteristics of Al-4Cu-4Mg composites produced by thixoforming process

Aluminium matrix composites have been widely developed due to its lightweight, therefore, Al composites have been potentially used for many application especially for vehicle components. Al-4Cu-4Mg reinforced Al₂O₃ has been successfully produced by the thixoforming process. In this study, Al-4Cu-4Mg as a matrix phase was prepared from Al ingot, Cu plate and Mg ingot and these materials were heated at 750°C, then Al₂O₃ particles with various from 5vf-% to 20vf-% were added into molten Al-4Cu-4Mg to produce composites using stir casting method. The stir cast composite was heated at 640°C to semi-solid state temperature then press as called thixoforming process. The effect of Al₂O₃ addition on characteristics and microstructure of stir cast and thixoformed composites are studied. The results show that thixoformed composites have better properties than that of stir cast composites, such as hardness, porosity and wear resistance. The porosities of thixoformed composites are lower with less Al₂O₃ content than that of high Al₂O₃content. The microstructures of stir cast composites are generally dendrite structure while thixoformed composites are columnar and globular which contributed to having better characteristic than that of dendrite structures. The hardness and wear resistance of thixoformed composites are higher than that of stir cast composite. It is also showed that composite containing 10vf-% Al₂O₃ provides optimum mechanical properties for both stir-cast and thixoformed composites.