Abstract
In order to develop corrosion resistance surface treatment method, we designed a chemical conversion treatment method which includes pretreatment to remove inclusions on a magnesium alloy and hydrothermal treatment to form the modifying layer.
One sample of MP1(ASTM: AZ31B) magnesium alloy was pretreated with hydrogen fluoride, followed by sodium hydroxide. Another sample was pretreated with sodium hydroxide, followed by sodium-gluconate solution. Then both samples were exposed to high temperature steam.
The number of inclusions, which may be Al-Mn intermetallic compound was dramatically reduced by both pretreatments. The hydrothermal treatment improved pitting corrosion resistance through the formation of the leather film which mainly consisted of magnesium hydroxide. The results of salt spray tests showed that the corrosion pits remarkably decreased after both pretreatments. Thus, the pitting-proof nature of the alloy was improved by combining chemical conversion and hydrothermal treatments.
In particular, the pretreatment of consisting of sodium hydroxide followed by sodium-gluconate solution, which is a toxic fluorine-free process, was found to be effective for use as a high corrosion resistance surface treatment method.
