PRESSURE DIE CAST GRAPHITE DISPERSED AL-SI-MG ALLOY MATRIX COMPOSITES

An improvement in casting of aluminium alloy graphite particulate comp osite synthesized by stir casting is discussed. About 15 wt.% graphite particles were dispersed in Al-Si-Mg (LM 25) alloy by the rheocasting technique. The composite ingots were used as a master alloy and dilut ed further with LM 25 alloy to obtain a 5 wt.% dispersion of graphite in the matrix. The composite ingots thus processed were subsequently r emelted and pressure die cast into plates. Macroscopic and microscopic examination of the plates revealed fewer defects and a fine distribut ion of particles. The ultimate tensile strength evaluated in this comp osite was superior (132-136 MPa) to that of gravity die cast (85-95 MP a) composites. The fracture toughness of the composites was in the ran ge 8-10 MPa m1/2.