Effects of Ca alone and Ca/Sr composite additions on microstructures, die castability, mechanical properties and creep properties of the Mg-Al based alloys are investigated for the purpose of the development of new Mg-Al-Ca-Sr alloy for automotive powertrain applications. Ca addition of more than about 1% to AM50 alloy significantly improves creep resistance but also enhance casting crack tendency. By the addition of approximately 0.2%Sr, such casting cracks are significantly suppressed, and besides creep resistance and mechanical properties increase. The improvement of creep resistance by Sr addition seems to be attributed to the suppression of grain boundary sliding due to the creation of thermally stable Al-Sr compound along the grain boundary and the suppression of discontinuous precipitation of -Mg 17 Al 12 phase.

Solid-state recycling for runner scraps of Mg-Al-Ca alloy was carried out by extrusion at 673 K and mechanical properties of the recycled Mg alloy were investigated by tensile tests. At room temperature, the recycled specimen showed a good combination of high ultimate tensile strength (348 MPa), high 0.2% proof stress (305 MPa) and large elongation (9%). Additionally, the recycled specimen exhibited superplastic behavior at 573 and 673 K. The excellent mechanical properties of the recycled specimen result most likely from fine dispersion of precipitates which is attained by hot extrusion.

Twin roll casting has been used to produce AZ31 magnesium alloy strip. The size of the cast strip is 5 mm thick and 250 mm wide. The microstructure of the as-cast AZ31 alloy strip consists of columnar zones from the surface to mid-thickness region and equiaxed zone in the midthickness region. The secondary dendrite arm spacing varies from 5.0 to 6.5 mm through the thickness and width of the strip and is much smaller than 34 mm of AZ31 alloy DC ingot used for the comparison. In temperature ranging from room temperature to 400 C, tensile strength and elongation of the as-cast strip are higher and smaller than those of DC ingot, respectively. Elongation is evidently improved by homogenization treatment and becomes more than that of DC ingot. Such an improvement of elongation is though to be caused by homogenization of segregation of Al and Zn atoms in the dendrite cell boundaries.

Twin roll casting has been used to produce AZ31 magnesium alloy strip. The size of the cast strip is 5mm thick and 250mm wide. The microstructure of the as-cast AZ31 alloy strip consists of columnar zones from the surface to mid-thickness region and equiaxed zones in the mid-thickness region. The secondary dendrite arm spacing varies from 5.0 to 6.5 μm through the thickness and width of the strip and is much smaller than 34μm of an AZ31 alloy DC ingot used for comparison. In the temperature ranging from room temperature to 400°C, the tensile strength and elongation of the as-cast strip are higher and smaller than those of DC ingot, respectively. Elongation is evidently improved by homogenization treatment and becomes more than that of the DC ingot. Such an improvement of elongation is though to be caused by homogenization of segregation of Al and Zn atoms in the dendrite cell boundaries. The non-homogenized and homogenized strips were subsequently hot rolled. Their hot rolled sheets have much higher value of elongation with equivalent strength, compared to the hot rolled sheet of flat-bar extruded from DC ingot in the temperature ranging from 200°C to 300°C.

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