Thermal spraying laser remelting composite technology

       2. Laser surface modification of Q235 steel surface by plasma spraying Al2O3-ω(TiO2) 13% ceramic coating (two-step method)



    Plasma spraying is the most widely used method for preparing ceramic coatings on metal surfaces, but it has the following inherent disadvantages: mechanical bonding between the coating and the substrate, poor impact resistance; high porosity of the coating, corrosion resistance and oxidation resistance Poor; the coating structure is uneven and the performance is unstable. In order to overcome the above shortcomings, laser technology was introduced to modify the surface of the sprayed ceramic layer to change its organizational characteristics and phase structure, thereby improving its performance.



    (1) Preparation of pre-coating According to the difference in physical and chemical properties of Q235 steel and sprayed ceramic materials, a stepped coating is designed as shown in Table 1. The substrate is sandblasted and then plasma sprayed. The spraying process parameters are shown in Table 2.



    (2) Laser remelting process Laser remelting uses a 2kW constant current electric excitation CO2 laser, and nitrogen is used as a protective gas. When laser remelting, it is necessary to select the appropriate laser power, spot size and scanning speed for different coatings. When the light spot is φ3mm and the scanning speed is 5mm/s, the optimal power corresponding to the coatings of Group A and Group B in Table 1 are 330W and 370W respectively. When the laser power is lower than the optimal value, the ceramic layer is not completely melted. The density is poor; while the laser power is higher than the optimum value, it will lead to the melting of the ceramic layer, the transition layer and the bottom layer.



    3. Plasma spraying laser surface alloying (two-step method)



    Table 3 lists the coating materials selected for laser surface alloying of AISI6150 steel substrates. The coating materials were first plasma sprayed and then melted and alloyed with a 1.2kW CO2 gas laser. After treatment, a non-porous, structurally complete alloyed layer is obtained.