Tensile-compressive asymmetry in extruded AZ31B rod and its effect on Profilometry-based Indentation Plastometry (PIP)

This paper concerns Tensile-Compressive Asymmetry (TCA) in a Mg-based alloy. Strong TCA is in general unusual, but previous publications have indicated that it can arise with the AZ31(B) alloy (in extruded rod or rolled plate form), such that there is a factor of up to two between yield stress values obtained by testing the same sample (in the same direction) in tension and in compression. This is confirmed in the present work. It has also been previously established that this effect is associated both with strong crystallographic texture and with the plasticity involving at least some deformation twinning. It is thus more likely with hexagonal metals, such as Mg, since their lower crystallographic symmetry (compared with cubic metals) favours this type of deformation. The microstructural evolution, and operative deformation mechanisms, that give rise to the observed TCA effects are investigated in detail here and at least most of the observed mechanical characteristics are rationalised. Finally, the Profilometry-based Indentation Plastometry (PIP) methodology for inferring stress-strain curves from indentation tests is applied to this material. As expected, full TCA characteristics cannot be obtained via PIP, but it is shown that there is a well-defined relationship between curves inferred in this way and the full set of uniaxial test outcomes.