Development of In Situ As Cast Al–Mg2Si Particulate Composite: Microstructure Refinement and Modification Studies

In situ processed hypereutectic Al–Mg2Si composites are reported as potential replacements for Al–Si–Mg heat-treated alloys in specific automotive applications like brake discs, cylinder heads and piston heads. Experiments were conducted for preparing as cast hypereutectic Al–15 %Mg2Si alloy, with 8 % extra silicon. The alloy microstructure revealed a dendritic morphology of α-Al, primary (P)-Mg2Si particles and Fe rich inclusions embedded in the ternary eutectic matrix. Addition of conventional grain refiner Al–5Ti–1B (1 %wt) lead to refinement of P-Mg2Si dendrites to faceted hopper-like polyhedral particles of ~30 μm in size. Addition of combination of B-rich grain refiner Al–1Ti–2B and phosphorous, resulted in finer (~20 μm), dense and fairly uniformly distributed P-Mg2Si particles in the microstructure. Electron probe microanalysis revealed the presence of free boron on all P-Mg2Si sites. Coupled compounds consisting of Ti, B and P were found to be associated with P-Mg2Si which may be responsible for enhanced refinement and modification of P-Mg2Si particles.