Effect of interfacial preheating on welded joints during ultrasonic composite welding

Due to the low welding energy efficiency of ultrasonic composite welding, preheating is proposed to concentrate the welding energy to joining interface. By analyzing the maximum shear load, fracture surface, and microstructure of the joint cross-sections, it is found that preheating can localize welding pressure because of the softening of the welding layers, which can further concentrate weld area and reduce the generation of welded edges. Preheating enhances the welding energy efficiency, reflected by improved weld attributes (weld area and the degree of bonding) and joint quality as preheating temperature increased. With extended preheating time, the maximum shear load increases, and then drops owing to the porosity generated in the weld layer when the joints are over-heated.