Ageing kinetics and precipitation hardening behavior of aluminum-silicon: A volume fractions examination approach

This work examines the ageing kinetics and precipitation hardening behaviour of ferrosilicon-silicon carbide reinforced aluminium metal matrix composites (AMMCs) with particular focus on the influence of varying the percentage volume fractions (%V_f) of reinforcement, ageing temperature and time on the material’s behaviour. The investigation systematically analyzed different %V_f of silicon carbide (SiC) of the AMMCs fabricated using dual stir casting technique; to examine the ageing kinetics, precipitation hardening behaviour and their impacts on the material’s mechanical properties so as to identify optimal ageing conditions for maximizing the performance of the composites. Percentage volume fraction and distribution of SiC particulates within the microstructure significantly affected the ageing kinetics and precipitation hardening behaviour; as higher %V_f of reinforcement led to a pronounced hardening effect which enhanced composite’s hardness by 45.98% and the yield strength by 46.28%. The activation energy of diffusion of the material increased with higher %V_f of SiC from 3508.508 J/mol at 0%V_f of SiC to 9170.342 J/mol at 25%V_f of SiC. This observed increment in activation energy follows the complex and enhanced diffusion pathway of Al-Si atoms, resulting in higher activation energy for the sustenance of the diffusion processes. The acceleration to precipitation hardening dropped with corresponding increase in ageing time. Thus, the precipitates hardening ratio (R) decreased from 0.9 with 5%V_f of SiC to 0.6 with 25%V_f of SiC at 100  ageing temperatures. A 15-20 %V_f of SiC offered a good balance between accelerated ageing kinetics and manageable activation energy, providing efficient hardening without excessively high diffusion barriers.