22MnB5 hot forming steel is widely used in the automotive industry due to the increasing demand for lightweight vehicles. As surface oxidation and decarburization occur during hot stamping processes, an Al-Si coating is often precoated on surfaces. The coating tends to melt into the melt pool during the laser welding of the matrix and reduce the strength of the welded joint; therefore, it should be removed. The decoating process by sub-nanosecond and picosecond lasers and process parameter optimization were conducted in this paper. The corresponding analysis of the different decoating processes, the mechanical properties and the elemental distribution was carried out after laser welding and heat treatment. It was found that the Al element has an influence on the strength and elongation of the welded joint. The high-power picosecond laser has a better removal effect than the lower power sub-nanosecond laser. The best mechanical properties of the welded joint were obtained under the process conditions of 1064 nm center wavelength, 15 kW power, 100 kHz frequency, and 0.1 m/s speed. In addition, the content of the coating metal elements (mainly Al) melted into the welded joint is reduced with increasing coating removal width, which significantly improves the mechanical properties of the welded joints. Al in the coating rarely melts into the welding pool when the coating removal width is not less than 0.4 mm, and its mechanical properties can meet the automotive stamping requirements for the welded plate.
Keywords: 22MnB5 steel; Al-Si coating; coating removal width; hot forming steel; laser removal.