Experimental Analysis on Ultrasonic Resistance Spot Welding of Aluminum Alloys

A recently developed hybrid joining process known as ultrasonic resistance spot welding (URW) was used on various pairs of similar and dissimilar aluminum (Al) alloys with different thicknesses, including AA5182–AA5182, AA6111–AA6111, AA7075–AA6111, and AA7075–AA5182, and comprehensively studied. Compared to conventional resistance spot welding (RSW), URW of the alloys showed consistently enhanced mechanical behavior in lap shear and crosstension tests. This can be attributed to the multiple perspectives on microstructure improvements. For different stacks of Al alloys and welding conditions, nugget formation was promoted with a larger nugget size in URW. In the nugget center, ultrasonically assisted (UA) vibration facilitated the formation of an equiaxed crystal zone. At the nugget boundary, URW showed a narrower coarse columnar zone and partially melted zone, which are associatedwith the lowest hardness in the weld. Specifically in dissimilar Al welds, UA vibration moved the nugget more centered toward the weld interface. These microstructure improvements indicated UA vibration can homogenize temperature and elemental distribution, which modifies solidification behavior.