Liquid Metal Embrittlement of Resistance Spot Welded 1180TRIP Steel - Effects of Crack Geometry on Weld Mechanical Performance

摘要

Transformation Induced Plasticity (TRIP) steels exhibiting favorable combinations of strength and ductility have received much attention for automotive applications. However, challenges to resistance spot weldability of zinc-coated TRIP steel such as low energy fracture and liquid metal embrittlement (LME) have emerged and require resolution prior to full implementation in the vehicle body structure. In this study, resistance spot welding Zn-coated TRIP1180 (1180 MPa minimum ultimate tensile strength) steel was conducted to produce spot welds exhibiting various levels of surface cracking. Static strength and fatigue life in the tensile loading mode were then evaluated in cross tension orientation. No significant reduction in cross tension strength, absorbed energy, and fatigue life was observed for tested samples containing cracks less than 325 μm in comparison to the crack-free welds, but the performance of the spot welds exhibiting large LME cracks (> 500 μm) was significantly reduced.