Gravity casting processing of brake discs: use of partially recycled Al-Si-Mg/SiCp composite

Brake discs of (Al-Si-Mg)/SiC composite were produced by gravity casting. To this purpose ingots, containing 50 vol.-% of SiC particles, produced by pressureless metal infiltration at Lanxide Corp., were melted, diluted with an unreinforced alloy (thus achieving a SiC content of 30 vol.-%), and cast in permanents moulds. The possibility of repeating the casting process using recycled material was investigated. Brake discs were fabricated by using 50 or 100% of recycled composite. The influence of material recycling on both microstructure and mechanical strength of composite items was studied by X-ray diffractometry, optical and scanning electron microscopy, and X-ray energy dispersive analysis. Tensile tests were carried out on round bars obtained contemporaneously to the discs by casting. Only a small decrease in strength and an increase in inclusion concentration resulted from material recycling. As brake discs have frequently to experience temperature changes, due to the friction occurring during braking, their sensitivity to thermal fatigue was investigated. Thermal cycling tests were carried out in the temperature range 25-220°C. In these conditions, only negligible material weakening was observed after 2000 cycles.