High strain rate superplastic behaviour of powder-metallurgy processed 7475Al+0.7Zr alloy

Superplasticity was investigated in powder-metallurgy (PM) processed 7475Al+0.7Zr alloy. Strain-rate-change (SRC) tests were carried out at various temperatures to examine the relationship between strain rate and flow stress. After the compensation by threshold stress, the superplastic flow was found to be well correlated with lattice diffusivity in aluminium, like that in the ingot-metallurgy (IM) processed 7475Al alloy having a coarser grain size. Large tensile elongations of up to 1000% could be obtained at a very high strain rate near 10−1 s−1 and at 515°C. Short fibre formation was observed after the superplastic deformation. This formation seemed to be related to liquid formation on the grain boundaries and similar evidences were found over a wide range of temperature, not necessarily near the incipient melting point.