AE Measurement during Friction Stir Welding of Flame-resistant Magnesium Alloy with Simulated Inclusions

Friction stir welding (FSW) is a solid state joining process. By inserting the tool with the pin at the tip into the material, friction heat is generated and it softens the material. The material plastically flows around the tool and the specimens are joined. Due to low heat input during FSW, the grain coarsening is suppressed. It was shown that higher strength at joints can be obtained compared with the conventional welding process in Al alloy and conventional Mg alloy. Recently, in order to reduce the environmental impact and improve the transportation efficiency of train body, flame-resistant Mg alloy was developed. In order to make railway vehicles, FSW is applicable to the joining of long plate of flame-resistant Mg alloy. To monitor the FSW process of flame-resistant Mg alloy, wireless AE streaming system was developed in our group. Although AE signals during FSW process was considered to be related to the defects in the welding zone, the relationship between the AE events and the defects is not clear. In this study, we introduced the defects by mixing the simulated inclusions and measured the AE signals by wireless AE streaming system. In the case of specimens with the simulated inclusions, higher AE RMS voltage was obtained compared with that without the simulated inclusions. Keywords: Friction Stir Welding; Acoustic Emission; Flame-resistant Mg Alloy; Joining Technology; Process Monitoring