Strain rate and temperature dependence of dynamic shear properties of Al–Sc alloy

Abstract

The dynamic shear deformation behaviour and fracture characteristics of Al–Sc alloy are studied using a split Hopkinson torsional bar at shear strain rates of 800, 1800 and 2800 s−1 and at temperatures of −150, 25 and 300°C. The experimental results indicate that the shear strain, shear strain rate and temperature all have a significant influence on the mechanical properties of the alloy. At constant temperature, the flow shear stress, fracture shear strain, work hardening rate, yield shear strength, work hardening coefficient, strain rate sensitivity and temperature sensitivity increase with increasing strain rate, while the activation energy decreases. Meanwhile, under a constant strain rate, the flow shear stress, work hardening rate, yielding shear strength, work hardening coefficient, strain rate sensitivity and temperature sensitivity decrease with increasing temperature while the fracture shear strain and activation energy increase. The Kobayashi and Dodd constitutive equation accurately describes the high strain rate shear plastic behaviour of Al–Sc alloy under the current test conditions. The fracture surfaces are characterised by transgranular dimpled features, which are indicative of ductile fracture. The appearance and density of these dimples are significantly dependent on the strain rate and temperature. The fracture surfaces of the gauge length section of the deformed specimen are twisted into band like features as a result of intensive localised shear deformation. This provides clear evidence of 'deformed' type shear bands. The width and microhardness of the shear band change with strain rate and temperature as a result of different work hardening effects. Specimen fracture initiates at the Al3Sc precipitate/matrix interface. The presence of precipitates accelerates the dynamic shear fracture formation through microcracking.