|
Abstract
|
Modified friction stir clinching (MFSC) with protuberance-keyhole leveling approach is employed in joining
dissimilar AA2024-T3/AA7075-T6 Al alloys. This technique is a two-step approach where friction stir clinching
is established in the first step while the inherent step-like (protuberance-keyhole cavity) is eliminated in the
second step. The microstructure, mechanical properties and fracture mode of the MFSC joints are examined and
compared with that of the conventional keyhole friction stir spot welds. The results reveal that the new approach
eliminates the formation of hook defect while geometric-differential flow-induced defects are formed in the
joint. Protuberance and shoulder indentation refilling processes form flow-induced defects at the weld center
and at the circumferential shoulder edges respectively. The severity of these defects is reduced via better intermixing
and flowability at high tool rotational speed. Atomic diffusion induces the formation of Al2CuMg and
Mg2Si phases in the joints (stir zones). A rise in tool rotational speed increases the tensile-shear and cross-tension
loads of the joint from 6798 N to 9487 N and 4366 N to 6850 N respectively. The new joining process improved
the joint quality due to enhanced effective bonded/shear area as compared to that of the conventional keyhole
friction stir spot welded joint.
|