MICROSTRUCTURE AND PROPERTIES OF 6082/7075 MAGNETIC-FIELD-ASSISTED RESISTANCE-SPOT-WELDED JOINTS

To advance automotive lightweighting, a study was conducted on steady-state magnetic-field-assisted resistance spot welding of 6082 aluminum alloy (1.0 mm thick) and 7075 aluminum alloy (1.5 mm thick) with thermal compensation. The influence of varying magnetic induction intensity on the microstructure and tensile properties of welded joints was assessed under the same welding current, time and electrode pressure. The results revealed that the Lorentz force induced by magnetic induction intensity ranging from 0 mT to 60 mT could promote an outward circumferential movement of molten metal within the weld nugget. This movement, at the same time, led to an increase in the weld-nugget size and improved the efficiency of thermal resistance. At a magnetic induction intensity of 80 mT, no weld-nugget formation occurred in the welded joint. Microstructural observations at magnetic induction intensities of 0 mT and 60 mT revealed equiaxed grains at the nugget center and columnar dendrite grains at the nugget edge in the welded joints. The Lorentz force accelerated the weld cooling rates after the addition of magnetic field, refining the weld grain structure. Tensile properties of the welded joints gradually improved with increasing the magnetic induction intensity from 0 mT to 60 mT, driven by the weld nugget size expansion and weld grain refinement. Overall, the present study indicated that the magnetic induction intensity of 60 mT resulted in the most favorable comprehensive mechanical properties of the investigated welded joints.