Effect of B₄C Content and Heat Treatment on the Microstructure, Mechanical Properties, and Tribological Behavior of...

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.