PARTICLE INCORPORATION BY MELT STIRRING FOR THE PRODUCTION OF METAL-MATRIX COMPOSITES

The production of ceramic particle-reinforced metal-matrix composites by the melt-stirring technique involves two different steps: firstly, the establishment of particle-melt contact, and secondly, the wetting of the particles by the melt. The wetting behaviour of metal-ceramic systems has been studied extensively, whereas the contacting problem has been largely neglected. In this paper, a novel in situ thermal method has been used to investigate the kinetics of particle-melt contacting, based on melt cooling during and immediately after the particle addition. An enthalpy balance relates the amount of cooling and the fraction of the particles contacting the melt. For the aluminium alloy (A356) with 15 vol % silicon carbide (17 mum diameter), it was found that only 16 % of the particles contacted the melt after mixing times of 15 min, but contact could be improved to 36 % by adding magnesium to the melt. The fraction contacting the melt agreed well with the particle volume fraction calculated independently. Sampling of the froth layer on top of the melt revealed that a large portion of the particles resides there prior to incorporation into the melt.