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The effect of heavy deformation on the structure of Mg-AZ31 alloy at ambientand elevated temperatures

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Constructional Mg alloys like AZ31 (96 wt % Mg, 3 wt % Al, 1 wt % Zn) reveal relatively low density (63% of pure Al density) together with good strength properties. However, their plasticity is low as well as deformability at room temperature, documented in the curves of nominal strain in dependence on relative strain shown in Figure 1. Their shape indicates that exceeding the instability point (maximum of the curve equivalent to Rm value) brings about nearly immediate failure of the specimen. It leads to the conclusion, that the ductility - a feature better describing deformability than elongation - is low. The deformability of Mg alloy increases significantly only at elevated temperature. The Mg‑based alloys, like AZ31 or AZ91 alloy is usually hot-deformed with the use of conventional methods like extrusion at least at 300°C [1]. Low ductility of hexagonal metals at low temperatures caused by the deficiency of easy-activated slip systems decreases their chance to use a method of Severe Plastic Deformation (SPD) as a way of grain structure refinement. Since the deformation at high temperatures is accompanied by the recrystallization process (dynamic or static one), the advantageous effects of plastic deformation are removed. That is why, cold pressing through an angular channel using an ECAP (Equal Channel Angular Pressing) method has become recently very promising when stable structure refinement using SPD is to be achieved. The ECAP is a process of intensive plastic deformation, in which the material is extruded with change of deformation path in the angular channel [2], where it is subjected to shear maintaining the dimensions of the cross‑section. The mentioned already change of the deformation path as well as a generated strong hydrostatic component of the strain field, is used in the ECAP process to prevent from formation of cracks in conditions of strong external constraints. The method enables to process r[...]

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