Research of microstructure and properties of resistance spot welded joints of galvanized DP steel for automobile

Abstract In this paper, the resistance spot welding of galvanized DP800 steel for Automobiles was done. The microstructure, mechanical properties and Fracture morphology characteristics of galvanized DP800 steel were studied by standard tensile tests, OM, SEM, etc. The results show that columnar crystal is formed in the melting zone of galvanized DP800 steel. The direction of growth is roughly perpendicular to the fusion line. The core area of the welding joint has Coarse Flat noodles Martensite, Ferrite, Bainite, and a small amount of residual Austenite. Two tissues exist in the thermal influence zone, namely Flat Martensite and Ferrite. The base material area is Martensite and Ferrite. When the welding process parameters of resistance spot welding are 10 KA, the welding time is 25 cyc, and the electrode pressure is 3 KN, the hardness value of the weld area reaches the maximum of 380 HV. There are both toughness and brittle fractures according to the different process parameters.