Research Progress on Coating Cracks in Galvanized Ultra-High Strength Steel Plates

The zinc coating plays a crucial role in protecting the steel plate substrate from oxidation and decarburization in the hot stamping protection of ultra-high strength steel for vehicles， and provides good cathodic protection and welding performance for parts.In the hot stamping of galvanized ultra-high strength steel plates， the diffusion of elements between the substrate and the coating and the generation of brittle phases(Г-phase) from the phase transformation in the coating contributed to the generation of micro-cracks in the coating and induced macroscopic cracks that extended to the substrate， resulting in a significant deterioration of the service life of the parts.Therefore， while ensuring that the galvanized ultra-high strength steel plate layer offers good protective and performance characteristics， it is essential to prevent the formation of coating cracks during the hot stamping process.The causes of microcracks and macrocracks in the galvanized layer were introduced， and the effects of hot stamping temperature (heating temperature，initial hot stamping temperature) and heating time，steel plate deformation，and steel plate substrate on the coating cracks were summarized.The contradiction points of the process required to improve the performance of the parts and inhibit the coating cracks were discussed with emphasis.The effects of friction factors on the coating cracks and forming properties were described， and the measures to inhibit the coating cracks were summarized.Finally， the development directions for inhibiting zinc-based coating cracks in the future were prospected from three aspects: the stress on the parts， the plastic deformation and the modification of the steel plate substrate.