Effect of rolling on tensile flow and fracture of Al–4.5Cu–3.4Fe cast composite

Al–4.5Cu–3.4Fe composite was cast in a heated cast-iron mould to obtain a structure consisting of needles of brittle Al3Fe intermetallic in a eutectic matrix of Al + Al3Fe. Pieces of this as-cast composite were cut in the form of small bars and deformed to large strain by hot rolling. Tensile tests were carried out on the rolled specimens at room temperature. The associated fracture surfaces were examined under a scanning electron microscope. With an increase in the extent of rolling, the needles of the brittle Al3Fe intermetallic were found to break down into progressively smaller fragments. At the same time the fragmented particles got oriented along the direction of rolling, the extent of orientation increasing with the extent of rolling. A gradual increase in ultimate tensile strength and ductility with an increase in the extent of rolling was observed. The poor mechanical properties of the as-cast composite resulted from the ‘coarse crystalline’ fracture which was caused by the cracking of the brittle second phase particles (Al3Fe). A transition from the coarse crystalline fracture in the as-cast condition to the form of void growth and void linkage occurred as the extent of rolling increased.