Investigating the effect of heat treatment on the fracture toughness of a hot extruded Al–Ti composite produced by powder metallurgy route

Abstract

An Al-5 wt% Ti composite was fabricated via powder metallurgy technique and hot extrusion. The produced composite samples were heat-treated subsequently at 600 °C for various time durations of 0, 4 and 10 h to achieve different volume fractions of the intermetallic Al3Ti phase. Pure aluminum sample was produced as a benchmark specimen to be compared to the composite samples. SEM studies were used to investigate the microstructure of the composite samples, and it was revealed that core-shell structured particles were formed in the composite heat-treated for 4 h. Triple point bending test was performed on the single edge notched beam specimens of the heat-treated Al-5 wt% Ti composite and the pure aluminum sample to investigate the bending strength and the fracture toughness. Two different methods of Kee and the fracture energy were implemented to evaluate the toughness of the Al-5 wt% Ti composites and the pure aluminum sample; the results indicated raising the heat treatment duration caused the fracture toughness (Kee) of the composite samples to decline, and the same trend was observed for the initiation and propagation fracture energies as well. By increasing the heat treatment time from 0 to 10 h, the fracture toughness of the composite dropped from 20.1 MPa m to 10.2 MPa m, while the pure aluminum sample had the greatest value of 25.6 MPa m. The SEM images of the fractured surface of the composite samples elucidated the effect of heating time on the fracture mechanism of the composites; the governing fracture mechanism changed from particle fracture for the composite heat-treated for 4 h to the particle decohesion for the one heat-treated for 10 h.