The properties of spraying and thermochemical reaction coating on the metal mold surface

The coatings were prepared on metal-mold surface by spraying method and thermo-chemical reaction method with A1₂O₃, SiO₂ and low melting point glass powder. The bonding strength of the coating with metal mold, the wettability of coating with aluminum alloy melt and the influence of coating on the casting surface roughness were analyzed. The results show that the thermochemical reaction method coating formed new phase of 3A1₂O₃·2SiO₂, Al₂SiO₅, the bonding strength of the thermochemical reaction method coating with metal mold up to 8.95 MPa, and the bonding strength of the spraying method coating with metal mold is only 0.97 MPa. The contact angle of aluminum alloy melt on thermochemical reaction method coating and spraying coating is 143.7° and 127.5° respectively, and the corresponding surface roughness of castings is 1.817 μm and 2.654 μm. After continuous casting of aluminum alloy, the thermochemical reaction method coating did not fall off, aluminium alloy casting surface is bright, clean and level, the roughness of aluminum alloy castings reaches to a level of R_a 1.0-2.0 μm.