Pseudo-in-situ stir casting: a new method for production of aluminum matrix composites with bimodal-sized B4C reinforcement

A new method was applied to produce an Al-0.5wt%Ti-0.3wt%Zr/5vol%B4C composite via stir casting with the aim of charac-terizing the microstructure of the resulting composite. For the production of the composite, large B4C particles (larger than 75 μm) with no pre-heating were added to the stirred melt. Reflected-light microscopy, X-ray diffraction, scanning electron microscopy, field-emission scan-ning electron microscopy, laser particle size analysis, and image analysis using the Clemex software were performed on the cast samples for microstructural analysis and phase detection. The results revealed that as a consequence of thermal shock, B4C particle breakage occurred in the melt. The mechanism proposed for this phenomenon is that the exerted thermal shock in combination with the low thermal shock resis-tance of B4C and large size of the added B4C particles were the three key parameters responsible for B4C particle breakage. This breakage in-troduced small particles with sizes less than 10 μm and with no contamination on their surfaces into the melt. The mean particle distance measured via image analysis was approximately 60 μm. The coefficient of variation index, which was used as a measure of particle distribu-tion homogeneity, showed some variations, indicating a relatively homogeneous distribution.