微細結晶粒を持つ高強度 Mg-Zn-Al-Ca-La 系 Mg 合金の摩擦攪拌接合性

抄録

  Friction stir weldability of a fine-grained high tensile strength Mg-Zn-Al-Ca-La magnesium alloy was evaluated by changing joining parameters, such as tool rotating speed and welding speed. Square butt joints with good quality were obtained at the conditions of welding speed 250-600 mm/min and tool rotating speed 16.7-25 s^-1, by using a tool with shoulder diameter of 15 mm, pin diameter of 5 mm and pin length of 3.9 mm. Higher welding speed or rotating speed led to the lack of bonding in the joint. Hardness at the center region of stir zone was slightly higher than that of the base metal, but hardness at the other region was slightly lower. It can be believed that the hardness of stir zone depends on the distribution and size of the inter-metallic compounds as well as the grain size of the recrystallized structure. Transverse tensile strength of friction stir welded joint was about 335 MPa, lower than that of the base metal (about 367 MPa). It was considered that the tensile strength of friction stir welded joint of Mg-Zn-Al-Ca-La magnesium alloy was strongly influenced by both the crystallographic orientation distribution and grain size.