Study On Zinc-Chromium Film Coating Nd-Fe-B

NdFeB permanent magnetic material is the third generation of rare magnetic material developed in 1980s,it can have excellent magnetic material performance, higher performance-cost ratio and abundant resources reserve, since it was discovered. Nd-Fe-B magnetic material have been produced rapidly in a short period, and permeate through each industrial field quickly. But because of Nd element is vivaciously active, the anti-corrosion performance of Nd-Fe-B permanent magnet is very bad. so how to improve surface protection of it is the key of improving product quality and long steady of performance.Protection of Nd-Fe-B as the purpose of this text, a kind of Zinc-Chromium chemical conversion film (called Dacromet in foreign country) has high corrosion resistance as well as no hydrogen brittle; no pollution, high temperature resistance, good combination with metals base and the organic coat, uniformity, and etc. so it is used widely. This article studied a kind of Zinc-Chromium film can be used in Nd-Fe-B magnetic material, at same time studied a kind of adapting pre-processes and analyse of result.1. Technological parameters of Zinc-Chromium film are the Zinc powder 262 350g/l,Aluminum powder 38⁴5g/l, CrO₃ 24⁵5g/l,additive in coat 6¹0g/l,baking temperature 250³20°C, baking time 15⁴0min.the best of them is the Zinc powder 300g/l, Aluminum powder 40g/l, CrO₃ 50g/l, additive in coat 8g/l, baking temperature 300°C, baking time 20 min.2. Film structure, phrase composition, element composition were studied using XRD,SEM,EDS,and XPS in detail. There are lots of Zinc and Aluminum powders in the film, which are combined by oxide, the combination between film and base metals also depend on oxide ,the structures have efficient protection to Nd-Fe-B bases. There is still about 0.51% (Element weight) of hexavalent Chromium in the film.3. The film structure was analysed, results show Zinc-Chromium film is the whole passivation of Zn, Al and base metals, The theory of film formation and mechanism of corrosion resistance are explained successfully.4. Comparison between Zinc- Chromium film and Zinc plating was made .Tt is show Zinc- Chromium film is much better than Zinc plating on corrosion resistance, so Zinc-Chromium film can substitute Zinc plating in this case.5. put out processes ,made pre-processed water to prohibit coat exploring and got 1000 hours in salt water experiment.