Forming of high corrosion and abrasion resistant surface films using magnesium oxide on magnesium alloys

开发了三种镁及镁合金表面改性新技术。在第一种技术中，注意到镁合金在腐蚀反应中形成的氢氧化镁。在腐蚀反应的早期阶段，氢氧化物均匀地形成以覆盖被腐蚀的表面，并且显示出相对弱的耐腐蚀性。但是，氢氧化物膜不能抑制随后的腐蚀反应，即丝状腐蚀。氢氧化镁的化学式为Mg（OH）_2，其脱水反应生成氧化镁MgO。通过将镁合金试样浸泡在高pH值溶液中，在试样表面形成稳定的氢氧化镁膜，进行人工腐蚀处理，然后将试样在673 K的空气中加热，进行氧化处理。当镁合金在空气中直接加热而不进行人工腐蚀时，与反应相反， ...更多信息 人工腐蚀后加热试样，试样表面形成稳定的氧化膜。氧化膜对盐浸试验中的丝状腐蚀有抑制作用，如AZ 31合金在盐浸试验中，丝状腐蚀持续时间约为30 ks，而未处理试样仅在1.7ks后就发生了丝状腐蚀。在盐浸试验的早期阶段，显示镁的腐蚀反应的氢气泡的形成被完全抑制。第二种方法是采用电化学方法来存款氢氧化物薄膜，而不是浸渍法。氧化处理是相同的，在空气中加热。在3%NaCl溶液中浸泡试验表明，经该工艺处理的AZ 31镁合金试样的腐蚀速率为4.2mg/cm^2/d，而经第一种工艺处理的AZ 31镁合金试样的腐蚀速率为8.6mg/cm^2/d。第三种方法是氟化物治疗。使用NaBF_4熔盐。将样品浸入673 K的熔盐中几十ks。表面膜由MgF_2和NaMgF_3组成，膜厚约10μm。对于AZ 31镁合金试样，采用第三种工艺后，在1%NaCl溶液中丝状腐蚀的抑制时间延长到1296 ks（15天）。在1%HCl和1%HNO_3等酸性溶液中，处理后的试样在20 ~ 30 ks内仍具有良好的耐蚀性。这三种方法都不会降低镁合金的再循环性能。少

Three kinds of new technique for surface modification on magnesium and its alloys have been developed. In the first technique, magnesium hydroxide formed in corrosion reaction on magnesium alloys is noticed. The hydroxide is uniformly formed to coat the corroded surface in the early stage of corrosion reactions, and shows a relatively weak corrosion resistance. However, the hydroxide film can not suppress the subsequent corrosion reaction, filiform corrosion. Glancing the chemical formula of the magnesium hydroxide, Mg(OH)_2, leads to the dehydration reaction to form magnesium oxide, MgO. By immersing the specimens of magnesium alloys into high pH solutions, stable films of magnesium hydroxide were formed on the specimens, artificial corrosion treatment, and then the specimens were heated in air at 673K, oxidation treatment. When the magnesium alloys are directly heated in air without artificial corrosion, brittle and porous oxide films are formed, in contrast to the reaction, when the … More specimens are heated after the artificial corrosion, the specimens are coated with stable oxide surface films. The oxide film can suppress the filiform corrosion in salt immersion tests, for example, in the case of AZ31 alloy, filiform corrosion occurred with duration time of about 30ks, while it occurred after only 1.7ks on the non-treated specimen. Evolution of hydrogen bubbles which show the corrosion reaction of magnesium is completely suppressed in the early stage of the salt immersion tests. In the second technique, electrochemical method is adopted to deposit the hydroxide films, instead of immersion. Oxidation treatment is the same, heating in air. Immersion tests using a 3% NaCl solution showed that the corrosion rate of the specimen of AZ31 alloy surface-treated by this technique was 4.2mg/cm^2/d, while that on the specimen treated by the first technique was 8.6mg/cm^2/d. The third technique is the fluoride treatment. Molten salt of NaBF_4 was used. Specimens were immersed into the molten salt at 673K for few tens ks. The resultant surface film was composed of MgF_2 and NaMgF_3 with about 10μm in thickness. The duration time for suppressing the filiform corrosion in 1% NaCl solution was prolonged to 1296ks (15 day) in the case of the specimen of AZ31 alloy by applying the third technique. Moreover, the treated specimens showed corrosion resistance even in the acid solutions such as 1% HCl and 1% HNO_3 solutions for 20 to 30ks. All these three techniques would not deteriorate the recycle ability in magnesium alloys. Less