Optimization of continuous drive friction welding process for AA6061-T6 circular pipe and conical head

Abstract

Aluminum alloy double-layer grid structure with bolt-ball joint has the advantages of light weight, corrosion resistance, convenient construction, etc. However, when circular pipe and conical head are connected by fusion welding, its strength is low. In order to solve this problem, the continuous drive friction welding (CDFW) process of aluminum alloy circular pipe and conical head and its strength of joint were studied in this paper. Based on the orthogonal experiment scheme, the CDFW experiments were conducted on AA6061-T6 circular pipe, then the tensile tests were completed on the standard samples to obtain joint efficiency under different welding parameters. The optimum welding parameters were determined by the method of variance and range analysis. The microstructure of joints was characterized by hardness test, OM, XRD, SEM, etc. The test results show that parameters affecting joint efficiency are friction pressure, rotational speed and upsetting rotational speed in descending order. Under the optimal welding process, the joint efficiency can reach 87.0%, which is superior to fusion welding. The fracture form of the welded joint is a mixture of intergranular and ductile transgranular fracture. WNZ is the crucial region of the welded joint, where the grain growth is greatly influenced by friction pressure. The friction pressure of the optimal welded joint is moderate, so the grains in WNZ are fine and grow adequately. The hardness softening of the welded joint also has certain influence on its mechanical properties. The solid solubility of the optimal welding sample is high and alloy elements are stable in the Al matrix, so it exhibits good mechanical properties. Finally, the CDFW experiments and tensile tests of circular pipe and conical head were conducted, which verifies the effectiveness of the optimal welding parameters.