Effect of tensile strain rate on high-temperature deformation and fracture of rolled Al-15 vol% B4C composite

Deformation behavior of a rolled Al-15 vol% B4C composite was studied at high temperatures, using single- tensile tests over a wide range of strain rates. The deformation of the composite is characterized by high apparent stress exponent, na and high activation energy, Qa, which are higher than those reported in pure Al. The analysis showed the presence of threshold stress that its value increases with decreasing the testing temperature. Using the threshold stress in the analysis, the obtained values of the true stress exponents, nt of ~ 5 and the true activation energy, Qt of 130 kJ mol−1, were similar to those reported for pure Al. TEM results of subgrain formation along with the mechanical data (nt and Qt) suggest that dislocation climb in the Al matrix is the rate controlling mechanism. The elongation (ef %) showed a maximum value at 500 °C at intermediate value of Zener-Hollomon parameter, Z. The fracture surfaces of tested samples are characterized by mixed modes of ductile (dimple formation) and brittle (cleavage) failures, which were dependent on the deformation conditions of temperature and strain rate.