RESISTANCE SPOT WELDING (RSW) EVALUATION OF UNCOATED 1.7 MM DIRECT STRIP PRODUCTION COMPLEX 700B (DSPC) STEEL FOR AUTOMOTIVE BODY STRUCTURAL APPLICATIONS

摘要

There has been a substantial increase in the use of advanced high strength steel (AHSS) 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. AHSS are gaining popularity due to their superior mechanical properties and use in parts for weight savings potential, as compared to mild steels. These new materials 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 often needed to weld these advanced steels.In this paper, the weld current lobes, mechanical properties (shear tension and coach peel), metallographic cross-section and microhardness profile of uncoated Direct Strip Production Complex 700B (DSPC 700B) 1.7 mm steel welded to itself in a two-metal stackup are discussed. Weld lobes were developed with Medium Frequency Direct Current (MFDC) equipment, ISO-type B20 tips, weld force of 5.78 kN and hold time of 5 cycles. The weld times were varied at 19, 24 and 29 cycles, with each producing current ranges at or below 4.0 kA. Tensile shear and coach peel samples were made at weld time of 19 cycles, with samples showing average loads of 18.38 kN and 3.14 kN respectively. Also, microhardness assessment using metallographic cross-sections were analyzed at three different weld cycles (19, 24 and 29 cycles). Similar heat affected zones (HAZ) and weld zones were observed for three different weld cycles.