Mechanical Properties of Magnesium Alloy Extrusions Processed from Machined Chips

Mechanical properties in the AZ9l magnesium alloy extrusions processed from machined chips were examined by tensile tests at 573 K to investigate superplastic behavior. The grains of the extrusions were almost equiaxed, which shows that grain refinement was achieved by hot extrusion. Grain sizes of the extrusions processed at 573, 673 and 753 K were 7.6, 15.4 and 60.1 μm, respectively. The extrusion processed at 573 K showed a maximum elongation of 230% at 3.3×10⁻⁴s⁻¹, which corresponds to the strain rate range where high m was found. For the extrusions processed at 673 K, a maximum elongation was about 100% at 1.7×10⁻⁴s⁻¹. For the extrusion processed at 753 K, elongations to failure were less than 30% at all strain rates. Cavities were nucleated for the extrusion processed from the machined chips, on the other hand, no cavity was observed for the extrusion processed from the cast ingot. For the extrusions processed from the machined chips, oxides which exist on the surfaces of the machined chips were dispersed by hot extrusion. Therefore it is pointed out that it is required to achieve more homogeneous dispersion of the oxide layers and smaller grain size in order to obtain excellent superplastic potential for the materials processed from machined chips.