Microstructural and mechanical properties evolution of magnesium AZ61 alloy processed through a combination of extrusion and thermomechanical processes

In this work, the microstructures and tensile properties of a commercial magnesium alloy “AZ61” processed by a combination of hot extrusion and thermomechanical processing (TMP) were investigated. The TMP was consisting of two or three hot rolling steps with large reductions per pass, thus allowing significant grain refinement. The microstructural evolution has been studied by means of optical and scanning electron microscopes, as well as X-ray diffraction analysis. The as-cast material is extruded in the form of a cylinder with initial diameter of 250 mm to a final diameter of 110 mm (80% reduction in cross-sectional area). Then hot rolling regimes were performed at 300 °C with different percentage of strain per pass. Tensile and hardness tests were performed in the samples (as-cast, extruded, and rolled) at room temperature in order to evaluate the mechanical properties of the material. The results of experiments demonstrated that fine grain size might be achieved in magnesium alloy AZ61 by using a two-step processing route involving an initial extrusion step followed by thermomechanical processing with large reduction in thickness per pass. This two-step process, designed to achieve average grain sizes of ∼10-20 μm.