Influence of Stir Flow on Joint Quality During Friction Stir Lap Al-to-Cu Welding

Abstract

Discontinuity free interface region of Al-to-Cu lap joints are required for high mechanical strength and low electrical resistance. While discontinuity free Al-to-Cu lap joints are difficult to produce using fusion welding, reviewing the literature, there is insufficient information on how such joints can be made by friction stir lap welding (FSLW). We will first briefly explain how material flow can cause voids, cavities or cracks during FSLW. Then, FSLW experiments are conducted using a tool design coupled with an appropriate positioning so that void-cavity free joints can be obtained. It has been found that speed conditions that cause insufficient downward flow also have resulted in insufficient formation of the interface layer thus in lack of joint. However, conditions that cause excessive downward flow also cause the intermetallic layer to crack. The balance of a mildly downward flow and a moderate growth of the interface layer without cracking will be demonstrated.