Journal of Welding and Joining

: Journal of KWJS. 2008;26(5):79-89. Published online November 12, 2008.; Evaluation on Resistance Spot Weldability and Nugget Formation of Surface Roughness Treated Steel Sheet; Ki-Hong Kim, Yung-Min Choi, Young-Seok Kim, Young-Mok Rhym, Ji-Hun Yu, Nam-Hyun Kang, Yeong-Do Park

Abstract: With the increased use of surface textured steel sheet in body-in-white assembly, resistance spot weldability of these steels is considered to be an important subject. This study evaluated nugget formation and weldability by measuring dynamic resistance with various weld pressure, current, and weld time for steel sheet with two different surface roughnesses. The surface roughness for T-H steel (R<SUB>a</SUB>=1.79 ㎛) was higher than that for T-L steel (R<SUB>a</SUB>=1.33 ㎛), and resulted in increased contact resistance and heating for T-H steel spot welding. Therefore, at low weld current and weld cycle ranges, the T-H steel showed better weldability over the T-L steel. The evaluations of weld interface showed that the fusion zone in the T-H steel sheet was continuous in contrast to discontinuous fusion zone for T-L steel sheet at the same welding conditions. A comparison of dynamic resistance and tensile-shear strength (TSS) between T-H and T-L steel sheet suggested that high surface roughness provided larger heating at early cycle of welding and larger TSS.

Keywords :Resistance spot welding;Weld nugget;Surface roughness;Dynamic resistance;Cold rolled steel sheet