Thermochemical computations and experimentation on deposition of aluminum and zinc on magnesium alloy

The feasibility of Al and Zn deposition on Mg alloys by means of thermal deposition and diffusion process is evaluated by means of thermochemical computations and experimentation. For the thermodynamic analysis, a closed system consisting of Al2O3 as filler, Al as donor, halide or halide compound as process activator and argon as inert gas was considered. ZnCl2 as activator was evaluated in the temperature range from 298 to 700 K. ZnCl2 is one of the best candidate compounds because the displacement reaction occurred between ZnCl2 and Al powder. The displacement reaction occurred between ZnCl2 and Mg near the substrate. The displacement reaction resultants are the Al chloride or Mg chloride and Zn. The analysis indicates that the depositions of Al and Zn on Mg take place through a mechanism on the surface followed by limited inward diffusion of Al and Zn. Thermal deposition and diffusion process have shown that by use of ZnCl2 activator, Al and Zn are deposited and then form Mg-Al and Mg-Zn intermetallic compounds. The process is simple and promising for the formation of corrosion and wear resistant coating on Mg. However, in order to provide a long-term protection, the coating should be deposited under conditions that eliminate through-thickness pores. Further developments are required in order to achieve dense, pore-free coating.