Influence of Tool Offsetting on the Structure and Morphology of Dissimilar Aluminum to Copper Friction-Stir Welds

In this work, a systematic analysis of the effect of tool offsetting on the morphological, structural, and mechanical properties of 6082-T6 aluminum to copper-DHP friction-stir welds was performed, enabling full understanding of Al-Cu bonding structure and failure mechanisms. Important relations between tool positioning and the thermomechanical phenomena taking place during welding were established. Tool offsetting was revealed to be an effective way of solving one of the most important concerns in Al/Cu friction-stir welding, i.e., the formation of large amounts of intermetallic-rich structures, which deeply influence the final strength and surface morphology of the welds. Actually, for welds produced without tool offsetting, it was found that the formation of fluidized intermetallic-rich structures promote the formation of internal decohesion areas inside the nugget, which have a detrimental effect on weld strength. For welds carried out with tool offsetting, intermetallic formation is almost suppressed, but important metallurgical discontinuities in the vicinity of large copper fragments, dispersed over the nugget, and at the nugget/copper interface were also found to have a detrimental effect on weld strength.