ＡＺ８０マグネシウム合金電子ビーム溶接継手の機械的性質

Abstract

AZ80 magnesium alloy plates with 5, 10 and 15mm thickness were butt welded using a high voltage electron beam welder with a capacity of 6kW (150kV×40mA). The optimization of welding conditions and microstructural observation have been carried out together with the mechanical tests on the electron beam welded joints, with the special reference to the effect of specimen plate thickness. Independent of the plate thickness, the welded joints were almost free from welding defects and showed good bead appearance under appropriate welding conditions. The arcing phenomena tended to appear with increasing plate thickness and decreasing active beam parameter. Both optimum beam current and welding speed were smaller than those for electron beam welded joints of aluminum alloys, while active beam parameter remained constant. For the plate thickness of 5 and 15mm, the penetration width was constant throughout the plate thickness. For the plate thickness of 10mm, however, the penetration width at top surface was different from that at bottom surface, resulting in a so-called wedge type bond zone. Regardless of the plate thickness, microstructure in the fusion zone was remarkably fine, although the grain boundary could not unambiguously detected. Hardness in the fusion zone was in good agreement with that of base metal. Both tensile strength and ductility of the welded joints were identical with those of base metal independent of the plate thickness. In tension tests of welded joints, fracture occurred either in heat affected zone or in base metal. The specimens notched into the center of fusion zone showed higher impact values than those of the base metal.