Microstructure and Properties of Pressure Die Cast Aluminium/Zirconium Silicate Composites

摘要

Al-7.3Si-2.4Mg alloy matrix composite dispersed with 15 mass%, zircon sand (zirconium silicate, ZrSiO_4) particles of 50 μm average particle size (APS) (20-200 μm size range) synthesized by stir casting was pressure die cast into plates. The zircon sand particles were uniformly distributed in the pressure die cast composite plates with refined Si, Mg_2Si and other phases along with finely dispersed gas porosities compared 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 matrix alloy (145 MPa) plates. The tensile fracture of pressure die cast composite showed particle cracking suggesting existence of good interfacial bonding between the particle and the matrix. The tensile properties of the pressure die cast composites at temperatures exceeding 423 K decreased sharply as a result of opening up of entrapped gas porosities. The dry abrasion wear tests showed only removal of the matrix and dispersed zircon sand particle offering resistance to wear when the abraded surface particle sizes were smaller (40 μm) than the zircon sand particles (50 μm) in the composites. On the other hand when the abrading surface had larger particles (400 μm) extensive wear of the composite took place by breaking of the zircon sand particles as well as by removal of the matrix.