The role of surface treatments and magnesium additions on the dispersoid/matrix interface in cast AlSiMg-15 wt.% SiCp composites

Abstract This article describes the metallography and scanning electron microscopy performed on fractured dispersoid/matrix interfaces in cast AlSiMg-15 wt.% SiCp composites. The effect of surface treatments to SiCp and of Mg additions to the melt were studied. The fractured surfaces of the composites showed a few reaction spots on the surfaces of SiC particles that had been pretreated with acetone and ultrasound applied, in contrast to the relatively clean surfaces observed with untreated particles and with heat-treated particles. The small gaps observed between the particles and the matrix when the former were untreated widened when the particles were subjected to the acetone/ultrasound pretreatment, but reduced when heat-treated particles were used. Additions of about 3 wt.% Mg to the meltproduced more reaction spots over the SiCp surface, especially in the case of untreated particles. The Mg additions were also found to reduce the interface gap. The optical metallography showed precipitation of eutectic Si as well as Mg2Si Phase adjacent to the interface. The role of the adsorbed gases on the surface of the SiCp in controlling the interface is discussed.