Preform cracking in squeeze cast magnesium based composites – effects of tooling temperature

In theory, a magnesium alloy should offer improved mechanical properties (such as higher strength and modulus) when reinforced with silicon carbide particulates or whiskers, as in the case of aluminium composites. However, unlike aluminium composites, the unique properties of magnesium composites are seldom achieved in practice, as reported in most published literature. Most of the magnesium composites reported were made using the squeeze casting technique, and the most notable effect is premature failure of the composites due to deformation and cracking of the preforms. This kind of perform damage has often been considered to result from use of excessive pressure in the squeeze infiltration step. Using computer modelling, an attempt was made to understand the relationship between preform cracking and the squeeze infiltration conditions of magnesium composites. The results of this work indicated that preform deformation and cracking can also result from improper processing temperatures. Therefore, relatively uniform temperatures in the liquid magnesium infiltrant are necessary in the fabrication of squeeze cast particulate reinforced magnesium composites to achieve acceptable mechanical properties.