Zn-induced liquid metal embrittlement and mechanical properties of advanced high-strength steel with resistance spot weld

Advanced high strength steels (AHSS) with zinc coatings are commonly jointed by using resistance spot welding (RSW). However, the steel/zinc alloy system causes the possibility of liquid metal embrittlement (LME). The role of zinc coatings on the plastic deformation and fracture mechanism of tensile and fatigue has not been systematically explored. In this study, the LME and mechanical properties of zinc-coated AHSS were systematically studied in terms of hot tensile tests by using bare and zinc-coated steel and lap-shear and fatigue tests utilizing RSW joints. The experimental results show that the zinc coating on the specimen surface damages the plastic deformation once the zinc coating appears, and the thickness of Zn coating remains constant regardless of temperature. LME cracking appears on one side due to the tilt of the electrode after the lap-shear test. The LME crack does not affect the fracture process of the fatigue test, as the fatigue crack and LME crack are located on opposite sides.