アルミニウム合金/鋼摩擦攪拌重ね合せ接合界面における層状組織の生成

抄録

Lap joining was carried out using friction stir welding (FSW) for 6022 aluminum alloy and low carbon steel sheets. Precise microstructural observation by a scanning and a transmission electron microscope were made in order to investigate the interfacial microstructure. Hardness measurement using nano-indenter was also performed to characterize the microstructural change at the weld interface. Characteristic laminate structure was formed in steel matrix in the vicinity of aluminum alloy/steel interface. TEM observation and an electron diffraction pattern analysis revealed that the laminate structure consists of periodical overlapping of two layers. One layer was a film formed by fine Fe grains, and the other was a film formed by the mixture of fine Al and Fe grains. Intermetallic compound particles (Al₁₃Fe₄, Al₅Fe₂) were also observed in the latter layer. Formation of an amorphous phase was also observed at the aluminum alloy/steel interface. It is considered that the laminate structure was formed by a repetitive mechanical alloying of Al and Fe grains below the rotating probe tip, which was slightly inserted into the steel sheet from the overlapped aluminum alloy sheet.