Microstructure and heat-treatment response of Al-2024/TiC composites

Composites of a commercial Al-2024 alloy reinforced with particulate TiC have been produced by the pressureless melt infiltration route. Infiltration was carried out at 1200°C for 2 h and composite materials containing 52 and 55 vol.% TiC were obtained. The phases other than the matrix and the reinforcement were identified as CuAl2, AlTi3, Ti3AlC, and TiAl3. It was found that the composites were age hardenable after solutionizing at 530°C for 150 min and subsequent natural or artificial ageing at 190°C. Mechanical properties of the composites, as-fabricated and heat-treated, showed a strong dependency on the ceramic content. After heat treatment, the 55% TiC composites showed an increase of hardness from 28.5 to 38.5 HRC; meanwhile ultimate tensile strength increased from 379 to 480 MPa. A similar behavior, as a function of heat treatment, was observed for the composites containing 52% TiC, but the estimated values were lower than those obtained for the 55% TiC composites. Scanning electron microscope (SEM) examination revealed transgranular fracture throughout the CuAl2 agglomerated precipitates in the as-fabricated composites. In the heat-treated conditions, brittle and intergranular fractures were observed.