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

Composites of a commercial Al-2024 alloy reinforced with particulate TiC ha ve been produced by the pressureless melt infiltration route. Infiltration was carried out at 1200 degrees C for 2 h and composite materials containin g 52 and 55 vol.% TiC were obtained. The phases other than the matrix and t he reinforcement were identified as CuAl2, AlTi3, Ti3AlC, and TiAl3. It was found that the composites were age hardenable after solutionizing at 530 d egrees C for 150 min and subsequent natural or artificial ageing at 190 deg rees C. Mechanical properties of the composites, as-fabricated and heat-tre ated, showed a strong dependency on the ceramic content. After heat treatme nt, 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 com posites containing 52% TiC, but the estimated values were lower than those obtained for the 55% TiC composites. Scanning electron microscope (SEM) exa mination revealed transgranular fracture throughout the CuAl2 agglomerated precipitates in the as-fabricated composites. In the heat-treated condition s, brittle and intergranular fractures were observed. (C) 2000 Elsevier Sci ence S.A. All rights reserved.