The effect of strontium on the microstructure, porosity and tensile properties of A356–10%B4C cast composite

This study was undertaken to investigate the effect of different concentrations of strontium (0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 1%) on the microstructure, porosity content and tensile properties of A356–10%B4C particulate metal matrix composite. In this work, the matrix alloy and composite were characterized by optical microscope, scanning electron microscope equipped with EDS and XRD. The composite ingots were made by stir casting process. The results showed that the addition of 0.03%Sr strongly modified silicon eutectic phase in A356 monolithic alloy, but 0.5%Sr was needed to complete the modification of A356–10%B4C composite. Results also demonstrated that Sr addition increases shrinkage porosity and generates new intermetallics in the microstructure. Further investigations on tensile tests revealed optimum strontium levels for improving tensile properties. In the point of fracture behavior of the composite, modified specimens with 0.2%Sr showed broken B4C particles and acceptable cohesion between B4C and matrix.