Resistance Spot Welding (RSW) Process Optimization for Coated and Uncoated Dual Phase 780 Steels

There has been a substantial increase in the use of advanced high strength steel in automotive structures in the last few years. The usage of these materials is projected to grow significantly in the next 5-10 years with the introduction of new safety and fuel economy regulations. Advanced High Strength Steels (AHSS) are gaining popularity due to their superior mechanical properties, and downgage potential for mass avoidance, as compared to mild steels. These new materials also pose significant manufacturing challenges, particularly for welding and stamping. Proper understanding of the weldability of these materials is critical for successful application on future vehicle programs. Due to the high strength nature of AHSS materials, higher weld forces and longer weld times are needed to weld AHSS materials. In this paper, weld lobe development for various gages of Dual Phase 780 (DP780) steel is discussed. Mid Frequency Direct Current (MFDC) weld equipment was used to weld three different stack up conditions. The weld lobes, mechanical properties (tensile shear and cross tension), cross-section examination, and microhardness of weld joint results are discussed.