EFFECT OF A MAGNETIC FIELD ON THE MICROSTRUCTURE AND PROPERTIES OF RESISTANCE SPOT WELDED JOINTS OF 444 FERRITIC STAINLESS STEEL/6082 ALUMINUM ALLOY

Abstract

To improve the welding quality of resistance spot welding joints of steel/aluminum lightweight structures, the steady magnetic field-assisted resistance spot welding method was used to weld 444 ferritic stainless steel and 6082 aluminum alloy, both with a thickness of 1 mm. Under the same welding parameters, the effect of a magnetic field on the microstructure and mechanical properties of the joint was analyzed. It was found that the Lorentz force generated by the addition of a magnetic field promoted the circumferential movement of the molten metal in the nugget zone, increased the size of the Fe/Al contact interface in the joint along the horizontal direction, and made an effective use of the heat generated during resistance spot welding. Although the intermetallic compounds in the intermediate transition layer of the two welded materials were mainly composed of (Fe, Cr, Si)Al2 and (Fe, Cr, Si)Al3, relatively low contents of (Fe, Cr, Si)Al2 and (Fe, Cr, Si)Al3 were found and a there was a significant decrease in the thickness of the intermetallic compound layer when the magnetic field was applied. Compared with the welded joint devoid of a magnetic field, the tensile strength and ductility of the joint were effectively improved, and the dimples in the fracture surface became relatively deep and numerous. In essence, resistance spot welding joints of steel/aluminum obtain better comprehensive mechanical properties when a magnetic field is applied.