A technique to remove zinc from aluminum alloy melts using vacuum arc heating was investigated. Zinc removal treatments for 4.6 kg of Al-1.2%Zn melt were carried out using a prototype zinc removal/recovery device which has a low-vacuum heating chamber for rapidly heating melt by arc discharge and a high-vacuum recovery chamber for promoting zinc evaporation. Melt temperature increased rapidly when the pressure of heating chamber was controlled at 600 Pa. In the heating chamber, zinc and aluminum evaporated perhaps due to the high-temperature of the arc discharge. Effective zinc removal in the recovery chamber occurred by controlling the pressure less than 60 Pa. Argon gas injection into the melt in the recovery chamber enhanced the zinc removal efficiency. Zinc concentration after the zinc removal treatment with the argon gas injection was about 0.02%.

  Mechanical joining methods such as self-piercing riveting (SPR) are used to join iron-based and aluminum alloy parts. However, low-ductility aluminum die-cast alloy often have cracks and insufficient quality. Therefore, a method has been proposed to locally recover ductility and prevent cracking while maintaining overall strength by rapidly heating and briefly heat-treating the joint area using laser or similar tool. This study aims to investigate the mechanical properties and microstructural changes in Al-Si-Mg-Mn-Fe die-cast alloys subjected to rapid heating and brief heat treatment, focusing on the mechanism of ductility changes. Heat treatment was carried out on alloy using a salt bath, and both mechanical properties and microstructures were examined. After rapid heating and brief heat treatment, the eutectic Si particles became more spherical as the heat treatment temperature increased. In the DSC curve, the as-cast material exhibited an exothermic peak at 510 K, but this peak disappeared after the heat treatment was completed. SEM and TEM observations showed no precipitates in the α-Al phase of the as-cast material, but precipitates were confirmed after the heat treatment. TEM analysis and elemental mapping indicated that the precipitates were Si. This suggests that Si was supersaturated in the α-Al phase in the as-cast state. The precipitation of Si in the α-Al phase contributed little to strength. On the contrary, it may have helped improve ductility. Synchrotron multi-scale tomography observations showed no significant changes in casting defects or intermetallic compounds due to the heat treatment, suggesting that they have a little effect on change of ductility. Therefore, the primary factors contributing to increased ductility of aluminum die-cast alloy after the heat treatment are stress concentration relaxation due to the spheroidization of eutectic Si particles and reduced connectivity of Si particles.