Advanced High-Speed Solid-State Joining of 2024 Aluminum Alloy Studs to 5052 Aluminum Alloy Plates

Abstract

Cylindrical 2024-T3 aluminum alloy studs were welded to 5052-H34 aluminum alloy plates by using an advanced high-speed solid-state joining method. Double cylindrical copper tubes, an assembly consisting of an inner tube and an outer tube, were used as electrodes. A stud having a circular ridge projection at its bottom was mounted at the end of the inner tube. The stud was then pressed against the plate surface. A discharge current was next introduced to the stud through the inner tube, whereupon the current flowed through the plate surface to the outer tube, which acts as a ground. The welding was completed within a few milliseconds without a notable increase in temperature of the joint. Subsequent examination revealed that the circular ridge projection had crushed and spread along the plate surface. Asymmetrical deformation occurred on both the inner side and outer side of the projection. The deformed area on the inner side of the projection consisted of a compacted grain structure. In contrast, the deformed area on the outer side exhibited a refined grain structure. These results indicate that the outside region was subjected to a higher temperature than the inside region. The joint was next investigated by tensile testing to evaluate its strength. The fracture surface of the joint region on the inner side of the projection exhibited a relatively flat surface with a limited number of dimples. On the other hand, that on the outer side was entirely covered with small dimples. Fracture stress was calculated by dividing the measured tensile fracture load by the dimple fracture area. The fracture stress thus obtained was found to be equivalent to the UTS of 5052-H34 alloy.