Hidetoshi Fujii

Large load friction stir welding of Mg–6Al–0.4Mn–2Ca magnesium alloy

ABSTRACT Friction stir welded (FSW) magnesium alloys usually exhibit a lower yield strength and elongation compared with base materials. In this study, large load FSW associated with an extremely low welding speed and rotation rate were applied to a non-combustive Mg–6Al–0.4Mn–2Ca magnesium alloy to modify the microstructure and texture in the weld zone and improve the mechanical properties of the joint. The twin structure in the stir zone provided adequate barriers for dislocation motion for strengthening and created more local sites for nucleating and accommodating dislocations, thereby elevating ductility and strain hardening in the transverse tensile test. The results showed that the yield strength and elongation of the joint were enhanced to 98% and 126% of the base material levels, respectively.

In situ chemical vapor deposition of metals on vapor-grown carbon fibers and fabrication of aluminum-matrix composites reinforced by coated fibers

Aluminum, nickel, silicon, and titanium were deposited onto the surfaces of vapor-grown carbon fibers (VGCFs) using a simple and cost-effective in situ chemical vapor deposition method. This process began with the in situ reaction of metal powders and iodine in heated quartz tubes, leading to the formation of metallic iodide vapors. Aluminum was deposited by annealing at 500xa0°C, forming almost homogeneous metallic aluminum layers on VGCFs. Aluminum-matrix composites reinforced by aluminum-coated VGCFs were fabricated by powder metallurgy. The tensile strength of these composites was improved by the aluminum-coating treatment. Nickel was deposited by annealing at 600xa0°C. The coating layer consisted of grains smaller than 5xa0nm. Molten aluminum was dropped on sheets comprising nickel-coated VGCFs, and the contact angle was measured; the wettability was found to be clearly improved. Composites containing nickel-coated VGCFs were fabricated via hot extrusion of a mixture of Al–7Si alloy and VGCFs at semisolid temperature. Vickers microhardness values of the composites were improved by nickel-coating treatment because of improved interaction of the aluminum matrix and VGCFs at the interface. A metallic silicon-coating layer was formed by annealing at 1100xa0°C. For titanium coating, the reaction of VGCFs with titanium and conversion of the VGCF surface into titanium carbide was confirmed. In the case of titanium, metallic titanium could be deposited without the use of iodine.