Effect of polycarbosilane precursor state on in-situ SiC formation and property enhancement in A356 aluminum alloy

This study examines the influence of precursor physical state on the in-situ formation of SiC ceramic reinforcement in A356 aluminum alloy using a polymer-derived ceramic route. Polycarbosilane was introduced through two methods: (i) Pyrolysis – powder route processed at 800°C (PP-800) and (ii) Pyrolysis – liquid route (spray injection) processed at 800°C (PL-800). Both processes were carried out at 800°C to isolate precursor-state effects under identical pyrolysis conditions. Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis – Differential thermal analysis (TGA – DTA) confirmed near-complete ceramization and SiC formation at ~ 800°C. Microstructural analysis revealed that PL-800 produced finer dendrites (Secondary dendrite arm spacing ≈25 ± 2 µm) and uniformly dispersed sub-micron SiC particles, whereas PP-800 showed coarser dendrites with grain-boundary-segregated SiC clusters due to delayed decomposition. XRD verified SiC formation in both routes, with significantly reduced Al4C3 formation in PL-800. Porosity was lowest for PL-800 (~0.8%), compared to 2.1% for PP-800. The PL-800 composite exhibited superior mechanical properties (Ultimate tensile strength ≈225 MPa, Yield strength ≈110 MPa, elongation ≈4.5%) owing to refined microstructure and cleaner interfaces. Overall, the ultrasonic spray-assisted liquid Polymer route is demonstrated as a more effective method for producing high-performance A356–SiC composites.