MICROSTRUCTURE AND PROPERTIES OF PRESSURE DIE CAST ALUMINIUM ZIRCONIUM SILICATE COMPOSITES/

Al-7.3Si-2.4Mg alloy matrix composite dispersed with 15 mass%, zircon sand (zirconium silicate, ZrSiO4) particles of 50 mu m average particl e size (APS) (20-200 mu m size range) synthesized by stir casting was pressure die cast into plates. The zircon sand particles were uniforml y distributed in the pressure die cast composite plates with refined S i, Mg,Si and other phases along with finely dispersed gas porosities c ompared to gravity die cast composites. The ultimate tensile strength of the pressure die cast composite plates (195-205 MPa) were superior to both gravity die cast composite (70 MPa) and pressure die cast matr ix alloy (145 MPa) plates. The tensile fracture of pressure die cast c omposite showed particle cracking suggesting existence of good interfa cial bonding between the particle and the matrix. The tensile properti es of the pressure die cast composites at temperatures exceeding 423 K decreased sharply as a result of opening up of entrapped gas porositi es. The dry abrasion wear tests showed only removal of the matrix and dispersed zircon sand particle offering resistance to wear when the ab raded surface particle sizes were smaller (40 mu m) than the zircon sa nd particles (50 mu m) in the composites. On the other hand when the a brading surface had larger particles (400 mu m) extensive wear of the composite took place by breaking of the zircon sand particles as well as by removal of the matrix.