Effect of B4C Content and Heat Treatment on the Microstructure, Mechanical Properties, and Tribological Behavior of Alumix–B4C Composites

The present study investigates the combined effect of B4C content and heat treatment on the microstructure, mechanical properties, and tribological behaviour of Alumix 431 matrix composites consolidated by field-assisted sintering technology/spark plasma sintering (FAST/SPS). Composites containing 5 wt.% and 10 wt.% B4C were examined in the as-sintered, solution-treated, and artificially aged conditions. Microstructural evolution was characterized by SEM/EDS, XRD, and TEM, while hardness, compression, and dry-sliding tests were used to evaluate material performance. Artificial ageing promoted the formation of fine MgZn2 and (Cu,Zn)Mg precipitates and substantially strengthened the matrix. The highest mechanical performance was obtained for the aged 5 wt.% B4C composite, reaching 172 HV1 and a maximum compressive stress of 742 ± 12 MPa. Increasing the B4C content to 10 wt.% did not further improve the mechanical properties because of greater microstructural heterogeneity. In contrast, the higher B4C content became beneficial under tribological loading after heat treatment, with the aged 10 wt.% B4C composite exhibiting the lowest wear rate after 500 m. Worn-surface analysis revealed predominantly abrasive wear accompanied by tribo-oxidation. The results demonstrate that composite performance is governed by the interaction between B4C content and the precipitation-strengthened matrix rather than by reinforcement content alone.