Researchers at the State Key Laboratory of Solid Lubrication of the Lanzhou Institute of Chemical Physics of the Chinese Academy of Sciences have developed a preparation method of magnesium alloy rare-earth conversion coatings for ethylene glycol coating system.

The method includes a process of pretreatment and activating and chemical conversion coating. The prepared rare-earth conversion coating has even thickness and good surface consistence, good adhesion between the substrate and coating, has good corrosion-resistant performance in ethylene glycol-water cooling liquid, and can solve the problem of the severe corrosion of engine cooling system used magnesium alloy in cooling liquid.

Lightweighting of automobiles is one of the most effective means to reduce oil consumption and emission. Magnesium alloy is widely considered as the promising material for lightweighting of automobiles. However, magnesium alloy has some shortcomings, such as low standard electrode potential, high chemical and electrochemical activity and poor corrosion resistance property in cooling liquid. All of these have limited the application of magnesium in cooling systems.

Cooling liquid is an indispensable heat transfer medium in engine cooling system. Currently, the mostly used commercial cooling liquid is ethylene glycol-water cooling liquid. The study on corrosion inhibiters for magnesium alloy in cooling liquid shows that the corrosion inhibiters which are effective in reducing corrosion of magnesium alloy in cooling liquid will corrode other metals severely. Therefore, the surface treatment of magnesium alloy is a better way to prevent the corrosion of magnesium alloy in cooling liquid.

The cooling system of engine cylinders is mainly cycle cooling pipe. The special shape and environment have limited the application of several techniques, such as microarc oxidation, vapor deposition, laser treatment, spraying treatment, etc. Nevertheless, the conversion coatings treatment can overcome the above shortcomings. But the existing methods all have certain disadvantages, such as environment pollution, uneven thickness, and complicated components of the solvent. There’s still no public preparation method of magnesium alloy rare-earth conversion coatings for ethylene glycol coating system applicable to engine cooling systems.

The researchers have received a Chinese invention patent for the technique on August 31. The patent is ZL 200810183390.5.