Research on high-temperature oxidation resistance, hot forming ability, and microstructure of Al-Si-Cu coating for 22MnB5 steel

High-temperature oxidation resistance, hot formability, element distribution, and microstructure of Al-10% Si-(0.5-3.0%)Cu coating were investigated by means of glow discharge spectroscopy, optical microscope, scanning electron microscope, and energy-dispersive spectroscopy. Results show that the addition of Cu can increase high-temperature oxidation resistance above 950 degrees C and improve hot formability so that no crack spreads into substrate steel as hot forming at 33.3% strain. Oxidation film structure is continual and compacting, and Si highly concentrates in the surface layer. The distribution of Cu has skin effect with peaking content 8.2% in the surface layer. After hot stamping, Al and Si diffuse into substrate steel, and Cu diffuses from inner to outer coating. Al-Si-Cu coating has smoother surface, straighter diffusion layer, and finer metal compound than Al-Si coating. Surface and diffusion layers are identified as aluminum oxide, Si-rich, and Cu phase and Al7SiFe2, Al3Fe, and CuAl3, respectively. Al-rich phase and the metal compound are composed of alpha-Al dissolving Fe, Si, and Cu and Al-Si matrix, Cu3Al, respectively.