Fabrication and growth mechanism of Al-Si coatings deposited on Mo substrate by hot dip plating technology

The Al-Si coatings with a low surface roughness were deposited on Mo substrate via the hot-dip plating technology, and the effects of deposition parameters on the microstructure, phase composition and surface roughness were systematically investigated. The results show that the hot-dip Al-Si coating is consist of a Mo(Si, Al)2 inner layer and an Al(Si)-Mo(Si, Al)2 outer layer. The coating surface is composed of Si(70.21-92.66 at%)-Al alloy phase containing Mo (Si, Al)2 grains and Al(73.83-92.32 at%)-Si alloy phase. With the increase of deposition temperature and the extension of time, the average grain area of Mo (Si, Al)2 increases from 0.264 mu m2 to 0.623 mu m2. The coating surface becomes smoother with the increase of deposition temperature, while rougher with the time. The maximum and minimum average surface roughness(RSa) values of the coating are 0.847 and 0.431 mu m, respectively. The coating thickness increased with the increase of deposition temperature and times. When the deposition temperature is 1000 degrees C, the thickness value of the Mo (Si, Al)2 layer of the coating increases in a parabolic law with deposition time, and the Kp(reaction rate constant) is 4.5 x10- 13 m2/s. The growth of coatings is essentially a process of depositing Al, Si elements in the form of Mo (Si, Al)2 intermetallic compounds on Mo substrate.