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In order to produce AZ91 and AZ31 magnesium alloy billets semisolid continuous casting by using an inclined cooling plate was carried out. The molten magnesium alloy in an electric furnace was flowed on the inclined cooling plate and then poured in a tundish. The slurry prepared using this process was solidified by drawing a dummy bar from a water-cooled copper mold, consequently producing a billet. As a result, we could produce the magnesium alloy billets by semisolid continuous casting. Magnesium alloy billets with refined and globular primary α crystals were successfully and continuously cast by optimizing the solidification conditions. In this case, the grain size of AZ91 billets was about 55μm and that of AZ31 billets was 50μm. The AZ91 billets produced by semisolid continuous casting were employed in thixocasting experiments. The experiments revealed that thixocasting could produce the mobile phone casings with spherical primary α crystals at 858K. Moreover, we proved that the difference of shot cycle did not influence the microstructures for up to 251 shots.

One new casting topic is semisolid casting technology. It requires solid-liquid coexistence in slurry containing fine and globular crystals surrounded by liquid metal. The authors have made such the slurry using an inclined cooling plate and continuously cast AZ91 and AZ31 magnesium alloys. The factors that influence the best slurry with fine and globular crystals are the casting temperature and the length and inclination angle of the cooling plate. This investigation describes the best casting and cooling plate conditions to make semisolid slurry of AS41B magnesium alloy. The best conditions are then applied to produce continuous casting billets of AS41B magnesium alloy using an inclined cooling plate and a horizontal continuous casting machine. A 60 mm diameter AS41B billet was successfully obtained, and globular crystals (average size 57 mm) appear in the microstructures.

The plate bending fatigue tests with stress ratio of -1 and 0 were conducted for the Mg-9mass%Al-1mass%Zn-2mass%Ca extruded plates, MIG joints and TIG joints. Fatigue limit of the plates along the extruded direction (ED) was smaller than that of the plates along the transverse direction (TD) for each stress ratio. It is likely that the anisotropy was attributed to the spread of basal pole in the ED and the rotation of basal pole toward the TD. Fracture occurred at the center of the specimens of MIG and TIG joints, and fatigue limits of both joints were lower than that of the extruded plates. Fatigue limit of TIG joints, however, was about 50 to 60% of MIG joints. SEM observations indicated that fatigue cracks initiated at the second phase particles (Al-Ca compounds) and propagated near them. Fracture occurred as a result of the crack connection. The size of the second phase particles in TIG joints was larger than that in MIG joints, so that the crack length was larger in TIG joints. It is likely that the larger size of the second phase particles was attributed to the lower fatigue limit of TIG joints.