Effects of Si addition on as-cast characteristics of Al-12Zn-6Mg-1Cu-xSi composites with 7.5vol% ZrO₂produced by squeeze casting

Aluminium matrix composites have superior properties and quality that make them ideal for almost any design and function, however the selection of reinforcement is incredibly vital to extend their strength and hardness. Zirconium oxide, which has good fracture toughness, is one option to improve the mechanical properties. This research studied composite materials with Al-12Zn-6Mg-1Cu-xSi as the matrix and reinforced by 7.5vol% ZrO₂. Silicon content was varied to 1, 3.86 and 4wt%, and samples were fabricated by squeeze casting. Materials characterization included Optical Emission Spectroscopy (OES), Rockwell B hardness testing, impact testing, microstructure analysis using an optical microscope and Scanning Electron Microscope (SEM). The results showed that the fabrication process was not able to produce plates with homogeneous ZrO₂distribution. The ZrO₂particles were found agglomerated and initiated porosities which then reduces the mechanical properties. This was due to poor wettability of ZrO₂particles in molten aluminium. The hardness and impact testing showed that the highest values were achieved by 1wt% silicon-containing alloy, with the values of 81 HRB and 0.0157J/mm², respectively. Increased mechanical properties which was expected with increasing silicon content was not achieved because of the presence of porosity.