Quasi-static and fatigue behavior of extruded ME21 and twin roll cast AZ31 magnesium sheet metals

Extruded ME21 (nominal thickness 1.5 mm) and twin roll cast AZ31 sheet metals (nominal thickness 1.2 mm) are investigated via quasi-static tensile and compressive tests and cyclic stress and strain controlled fatigue tests at ambient temperature. Both materials show a strong basal texture with the c-axis being almost normal to the sheet plane in AZ31 and tilted about 20° from the normal towards the extrusion direction in ME21. Furthermore, a direction dependence of the tensile strength values is observed. The difference in tensile yield strength comparing the extrusion (rolling) to the transverse direction is about 10% in AZ31 and 25% in ME21. In compression the quasi-static stress-strain curves show negligible differences in extrusion (rolling) and transverse direction up to 10% total strain. ME21 shows comparatively low tangent modulus and pseudoelastic behavior at low stresses. Sigmoidal shape of hysteresis loops starts to appear at strain amplitudes >0.4% in both materials. The cyclic stress-strain curve is approximated by the Ramberg-Osgood equation using different parameters for tension and compression. The strain-life curve is described by the Basquin equation and the bilinear Manson-Coffin approach. In addition, the evolution of mean stress, stress amplitude, and Masing behavior are analyzed and strain- and stress-life curves of both materials are compared and discussed.