Study the effect of the friction stir process on the microstructure and mechanical behavior of the AZ31 as-cast alloy joint

The AZ31 magnesium alloy has a significant potential for the aircraft manufacturing industry due to its low density and proper mechanical properties. In this research, the Gas Tungsten Arc Welding (GTAW) process was used by applying pulse current for the AZ31 as-cast alloy joint. The GTAW process is conducted by pulse time, voltage, and equivalent current of 0.5 sec, 12 V, 187.5 A, respectively. Then, the surface of welded joint by the GTAW was improved using friction stir processing (FSP). The effect of FSP on the microstructure and mechanical properties of this joint was examined. Subsequently, the friction stir processing was performed with a tool rotating speed of 1120 rpm, the tool traverse speed of 50 mm/min in two passes behind and on the welding line. The microstructure and fracture sections of the prepared samples were respectively examined by optical microscopy and scanning electron microscopy (SEM). The mechanical behavior of the samples was studied using tensile, micro-hardness and impact tests. According to the results, the microstructure of the welding region of the TIG sample included highly fine homogeneous and coaxial grains. After the friction stir process (FSP), the microstructure transformed into fine and structural grains in the form of a ring-shaped morphology. The FSP resulted in a 23% improvement in the tensile strength of the TIG sample. Also, the impact energy of the welding metal increased by about 37%. In general, the mechanical behavior of the joint was improved after applying the friction stir process.