Dependence of flow strength and deformation mechanisms in common wrought and die cast magnesium alloys on orientation, strain rate and temperature

Abstract

The controlling plastic deformation mechanisms (i.e. slip or twinning) and the structural crash performance of Mg alloys are strongly influenced by loading mode, texture and microstructure. This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions (AM30 and AZ31), sheet (AZ31), and high pressure die castings (HPDC, AM50 and AM60). Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature (i.e. 0.00075–2800 s −1 and 100 °C to −150 °C) using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar (SHB) apparatus. In primarily-slip-dominant deformation, the true stress–strain curves showed approximate power-law behavior, and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter, T ln ( 5.3 × 10 7 / ɛ ˙ ) where T is test temperature in Kelvin and ɛ ˙ is strain rate in s −1 . In primarily-twin-dominant deformation, the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s −1 owing to the athermal characteristics of mechanical twinning; the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.