Preform cracking in squeeze casting of particulate reinforced magnesium matrix composites

The performance of a squeeze cast particulate reinforced metal matrix composite is critically dependent on the processing conditions used. These conditions will determine the state of stress, and the interfacial reactions (occurred between the particles, binder and the matrix alloy) in the as fabricated composite. In squeeze casting a paniculate reinforced composite, the major processing steps involved are the fabrication of a particulate preform and the subsequent squeeze infiltration of molten metal into the preform. In this study, SiC particulate reinforced magnesium composite system is used as an example. First, SiC particulate preforms were fabricated. Second, different processing parameters such as the casting temperature, tooling temperature, pressure application, and press speed were employed to squeeze infiltrate molten magnesium into the preforms to form composites. One of the most undesirable effects commonly found in squeeze cast magnesium based composites, is the cracking of preforms. This effect is often believed to be attributed to the excessive amount of pressure used during the squeeze infiltration step. With the use of computer modeling, an attempt was made to understand the relationship of preform cracking with the squeeze infiltration process of magnesium based composites. The results of this work indicated that preform cracking can be resulted from a combination of processing conditions other than high squeeze casting pressure.