Optimization of Spark Plasma Sintering Joining Process of 7075-T6 Aluminum Alloy

The 7075-T6 aluminum alloy was joined by spark plasma sintering technique. The effects of base metal surface pretreatment (400^# sandpaper grinding, chemical etching, 400^# sandpaper grinding + chemical etching and 2000^# sandpaper grinding + chemical etching), heating rate (10, 30, 50 °C · min⁻¹), joining temperature (450, 470, 490, 510 °C), joining pressure (4.5, 5.0, 5.5, 6.0, 7.0 MPa) and holding time (45, 60, 75, 90, 120 min) on the joining quality, shear properties and thinning rate of the joint were studied by single factor method, and the appropriate surface pretreatment process and the optimal process parameters were obtained. The results show that the appropriate surface pretreatment was 400^# sandpaper grinding; at this time the joining quality of 7075-T6 aluminum alloy joint was the best, there were few unclosed holes in the joint interface, and the bonding rate was largest with value of 71.7%. With the increase of heating rate, the joining quality of the joint became worse, but the bonding rate was higher than 76%, and the shear strength and thinning rate of the joint decreased. With the increase of the joining temperature or the joining pressure, the joining quality of the joint became better, and the bonding rate, shear strength and thinning rate of the joint increased. However, when the joining pressure was greater than 6.0 MPa, the increase of bonding rate and shear strength decreased, while the thinning rate increased significantly. With the increase of holding time, the variation of the bonding rate, shear strength and thinning rate of the joint was small. The optimum joining process of 7075-T6 aluminum alloy was heating rate of 50 °C min⁻¹, joining pressure of 6.0 MPa, joining temperature of 490 °C and holding time of 45 min. At this time, the bonding rate of the joint was 81.3%, the shear strength was 132.9 MPa, the thinning rate was 1.91%, and the shear fracture mode was ductile fracture.