Influence of Si element content on the LME sensitivity of high strength steel for automobiles during spot welding process

Advanced hot-dip galvanized high-strength steel is widely used in automotive exterior plates and various sill beam workpieces due to its excellent corrosion resistance by anodic protection. It could also meet the need for lightweight in the automotive industry. In the process of resistance spot welding, the zinc-coated layer on its surface will diffuse into the matrix along grain boundaries because the zinc-coated layer melts during the high-temperature and high-pressure process of spot welding. In the subsequent cooling process, the LME cracks are initiated under the complex stress field of tension and compression. The higher Si element in the matrix will inhibit the binding of Zn and Fe elements, thereby promoting the continuous diffusion of Zn into the matrix and eventually increasing the LME crack sensitivity. It can also be found in the in-situ tensile test that the crack propagation rate of high Si content steel is faster than that of low Si steel. In this paper, the influence of Si content on the initiation and propagation of LME micro-cracks was studied.