Resistance Spot Welding of Zn-Coated Third Generation Automotive Steels Using Mid-Frequency Direct Current Technology

The weight reduction through the use of lightweight materials started to play an important role in improving fuel economy and reducing carbon dioxide emissions. The car makers focused their intention on the use of zinc-coated advanced high strength steels for light weighting, collision safety and corrosion resistance. In this study, weldability of zinc-coated TRIP-aided bainitic ferrite steel was studied by resistance spot welding. The welded joints were produced by mid-frequency direct current technology working in DC current. In order to determine liquid metal embrittlement cracks, the welded joints were subjected to magnetic particle test as well as macro/microstructure investigations. According to tensile-shear and cross-tensile tests, the highest strength was obtained at 8 kA current. However, a decrease in strength was observed with an increase of welding current due to the metal expulsion. In addition, hardness measurements were taken on the welded joints with different welding currents for a comparison. [GRAPHICS] .