Mechanical properties of a spray-cast aluminum alloy processed by severe plastic deformation

Experiments were conducted to evaluate the mechanical properties of a spray-cast Al-7034 alloy processed by severe plastic deformation. The alloy was received with an average grain size of ∼2.1 μm and processed by equal-channel angular pressing (ECAP) at a temperature of 473 K to give a grain size of ∼0.3 μm after 6 or 8 passes. Following ECAP, the mechanical properties were evaluated at room temperature (298 K) and at an elevated temperature of 673 K. In tensile testing at ambient temperature, the stress-strain curves show very short regions of strain hardening after ECAP and low values for the ultimate tensile strength by comparison with the unpressed alloy. This lack of strength is due to the high pressures imposed by ECAP and the consequent fragmentation and dissolution of the rod-like MgZn₂ precipitates. It is shown that the strength may be restored by performing an appropriate ageing treatment after ECAP. Superplastic ductilities were recorded at a temperature of 673 K with tensile elongations exceeding 1000%. Careful inspection of the polished surfaces of samples pulled to fracture in the superplastic condition revealed the occurrence of extensive internal cavitation. Quantitative measurements showed the development of these internal cavities is consistent with conventional superplastic alloys.