Corrosion action and passivation mechanism of magnesium alloy in fluoride solution

• Published in: Transactions of Nonferrous Metals Society of China Vol. 19; no. 1; pp. 50 - 54
• Main Author: 李建中 黄久贵 田彦文 刘常升
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2009; Steel Sheet Cold Rolling Plant, Baosteel Branch, Baosteel Co., Ltd., Shanghai 200431, China%Steel Sheet Cold Rolling Plant, Baosteel Branch, Baosteel Co., Ltd., Shanghai 200431, China%School of Metallurgy and Materials, Northeastern University, Shenyang 110004, China; School of Metallurgy and Materials, Northeastern University, Shenyang 110004, China
• Subjects: corrosion; fluoride; magnesium alloy; nickel sulfate; passive film; 硫酸镍; 金属腐蚀; 镁合金; fluoride; magnesium alloy; corrosion; nickel sulfate; passive film
• ISSN: 1003-6326
• DOI: 10.1016/S1003-6326(08)60227-7

Corrosion action and passive mechanism of magnesium alloy in the fluoride solution were studied by means of scanning electron microscopy（SEM）, energy dispersive X-ray spectroscopy（EDS）, and electrochemistry methods. The results show that an insoluble MgF2 fihn is generated on the surface of magnesium alloy activated in the hydrofluoric acid. And the mass of the deposited MgF2 film may reach a constant value, when the mass ratio of Mg/F on the magnesium alloy surface is fixed at 11.3：1. The activated magnesium alloy gains a ＇passivation state＇ in a mixture of sulfuric acid and hydrofluoric acid at a volume ratio of less than 1.2. At the same time the mass of magnesium alloy is maintained as a function of the time. When the ratio is above 1.4, the mass of magnesium alloy rapidly decreases. The passive film formed through adsorption of HF2- （or H2F3, H3F4-） ions by the deposited MgF2 film can protect the magnesium alloy from corrosion in fluoride solution, but not in non-fluoride solutions. The passive state is maintained for activated magnesium alloy in an acidic sulfuric nickel solution with added fluoride. If fluoride and carbonate are added to the acidic sulfuric nickel solution, a replacement reaction between magnesium alloy and solution takes place.