In this study, solidification structure changes under electromagnetic force (EMF) were examined for Al-10Fe and Al-25Si alloys. One directional EMF was induced by applying DC currents of 100A and 130A with static magnetic fields. Solidification structure was examined using an optical microscope, X-ray computed tomography, and X-ray fluorescence mapping. When EMF was imposed from above the liquidus temperature, primary crystals were not segregated into one side of the ingots and instead were found to be segregated all along the ingot periphery for both Al-10Fe and Al-25Si. A fine hypo-eutectic structure containing Al dendrites was observed in areas devoid of primary crystals in the central parts of the Al-25Si ingots. These segregation phenomena of primary crystals did not occur when EMF was imposed from the point below the liquidus temperature, suggesting that EMF does not exert an effect on free crystals existing in the liquid metal. It also suggests that segregated primary crystals were not moved towards the periphery by EMF. It may prevent nucleating primary crystals from separating from the wall surface, hence enhancing nucleation on the wall and dense growth of crystals from the wall surface, resulting in a highly segregated solidification structure.

The relationship between the stress state and the deep-drawn deformation structure of Mg-1.5Zr alloy was studied. The alloy blanks, made from cast material, were deep-drawn at 300°C with a drawing ratio of 1.7. A series of circular laser-etched marks, made on the blank surface from the center to the rim of the blank, were used to measure strains in various directions caused during deep-drawing. The results indicated that since no shear stress is generated at the bottom of the cup due to equal biaxial tension, slip deformation is unlikely to occur and hence no development of basal texture is observed, however a large number of twins were formed. The R part of the cup is also biaxially tensioned, but the shear stress is |σ_r-σ_θ| and conjugated shear stress is generated due to bending, which promotes the formation of new crystals and twin deformation. Along the side wall from the R toward the rim areas of the cup, there is a transition area where σ_θ changes from tension to compression and as compression strain increases, basal texture develops significantly. The main deformation mechanism is by twin when σ_θ is “tensile” and by slip when σ_θ is “compression”.

Pure magnesium powders together with different amounts of process control agent (PCA) were mechanically milled using a vibration ball mill, which provide higher energy to the powder than a planetary ball mill. Obtained powders were consolidated into bulk materials by the spark plasma sintering (SPS). Changes in hardness and solid-state reactions of the MMed pure magnesium powders and the bulk materials have been examined by hardness measurements and an X-ray diffraction. The Vickers hardness of the pure magnesium powders increased to 65 HV after MM 2 h with 0.30 g of PCA. The Vickers hardness of the bulk materials fabricated from MM 4 h pure magnesium powders with 0.40 g of PCA increased to 60 HV. Those hardness values were higher than that of using planetary ball mill. Vibration ball mill was attributable to increase the hardness of MMed powders and bulk materials due to minimized crystallite size in a short MM time together with formation of compounds.

Plate bending fatigue tests were conducted for the Mg-9mass%Al-1mass%Zn-2mass%Ca alloy joints prepared by friction stir welding under two different conditions of stress ratio of 0 and -1. The fatigue limit of the FSW joints was above 80% of that of base metal under all test conditions. Fracture origin was observed at the thermo-mechanically affected zone (TMAZ) in the FSW joints. The fatigue limit of the FSW joints were higher than that of the metal inert gas (MIG) and tungsten inert gas (TIG) joints. Fracture origin was observed at the fused zone (FZ) both in MIG joint and TIG joint. The grain size and second phase particle size were larger in the FZ than in the TMAZ, and hence higher fatigue limit of the FSW joints compared with that of the MIG and TIG joints was attributed to the fine microstructure in TMAZ of FSW joints.

Metallic hollow sphere is a kind of lightweight metal foams. Most metallic hollow spheres have been made of iron. The authors have succeeded to fabricate Mg-Al-Zn alloy hollow spheres through inert gas foaming in the previous study. In the present study, magnesium alloy hollow spheres are fabricated through atmospheric foaming. The starting material was AZX912 flame-retardant magnesium alloy plates. AZX912 alloy precursors were produced through accumulative diffusion-bonding process. Magnesium hydride powder with the total amount of 1.0 mass% was used as a foaming agent. Foaming tests were carried out in atmosphere using a high-frequency induction heating system. The foaming process was in-situ observed by the digital video camera. The AZX912 alloy precursor expanded with increasing the heating time. As a result, AZX912 alloy hollow sphere with the porosity of 50% was obtained successfully. The hollow sphere easily floated on the surface of water because of the specific gravity of 0.91 and the closed-cell structure.