Mika Tsunakawa

Preparation of Corrosion-Resistant Films on Magnesium Alloys by Steam Coating

This chapter introduces a novel, chemical-free “steam coating” method for preparing films on magnesium (Mg) alloys and assesses their effectiveness in improving the corrosion resistance of two different Mg alloys. A film composed of crystalline Mg(OH) 2 and Mg-Al layered double hydroxide (LDH) was successfully formed on AZ31 Mg alloy, and its corrosion resistance was evaluated through electrochemical measurements and immersion tests in an aqueous solution containing 5 wt.% NaCl. An anticorrosive film was also formed on Ca-added flame-resistant AM60 (AMCa602) Mg alloy via the same steam coating method and found to be composed of crystalline Mg(OH) 2 and Mg-Al layered double hydroxide (LDH). Its corrosion resistance was also investigated, and the effectiveness of the steam coating method for improving the corrosion resistance of Mg was fully explored.

Preparation of corrosion resistant film on Mg-6Al-1Zn-2Ca alloy by steam coating

Corrosion resistant films were prepared on flame-resistant Mg–6Al–1Zn–2Ca (in mass%) alloy by steam coating using ultra pure water as steam source. The prepared films were characterized using SEM, XRD, and FT-IR. Corrosion resistance of the film was estimated by polarization curve measurement in 5 mass% NaCl aqueous solution. All XRD patterns of the films coated Mg–6Al–1Zn–2Ca alloy revealed that all films were composed of crystalline Mg(OH)2 and Mg–Al layered double hydroxide (LDH). FT-IR spectra showed that the Mg–Al LDH had carbonateand nitrate-ions in the interlayer. Potentiodynamic polarization curves of the film prepared at 433 K for 6 h indicated that the corrosion current density decreased by more than four orders of magnitude as compared to that of the uncoated Mg–6Al–1Zn–2Ca alloy. (Received May 22, 2017 Accepted July 17, 2017)

Formation of Corrosion Resistant Mg(OH)2 Film Containing Mg-Al Layered Double Hydroxide on Mg Alloy Using Steam Coating

In recent years, a reduction in weight of materials is highly desirable in the fields of transport industry and information technology devices. Magnesium (Mg) alloys have excellent physical and mechanical properties such as low density, good electromagnetic shielding, and high strength/weight ratio. Unfortunately, they have a great issue that is low corrosion. Thus, it is very important to develop surface treatment technologies to improve the corrosion resistance of magnesium alloys. Many surface treatments such as chemical conversion, anodic oxidization, and electroplating have been developed. However, there processes require multi-step pretreatments and waste liquid treatments. Thus, the development of a simple, easy, and low-cost surface treatment is highly desirable. In this paper, we report a novel preparation method of anticorrosive film on Mg alloy by steam coating and the corrosion resistance of the film. The prepared films were characterized by XRD, SEM, EDX, and electrochemical measurements. Polarization curve measurements demonstrated that the Ecorr and icorr values were found to be most positive potential and lowest current density in all the samples, indicating that the sample had best corrosion resistant performance.

Rapid Fabrication of a Crystalline Myristic Acid-Based Superhydrophobic Film with Corrosion Resistance on Magnesium Alloys by the Facile One-Step Immersion Process

A simple, easy, and rapid process of fabricating superhydrophobic surfaces on magnesium alloy AZ31 by a one-step immersion at room temperature was developed. The myristic acid-modified micro-/nanostructured surfaces showed static water contact angles over 150° and water contact angle hysteresis below 10°, thus illustrating superhydrophobic property. The shortest treatment time for obtaining the superhydrophobic surfaces was 30 s. In addition, we demonstrated for the first time that crystalline solid myristic acid could be formed on a Mg alloy using a suitable molar ratio of Ce ions and myristic acid. The contact angle hysteresis was lowered with an increase in the immersion time. Potentiodynamic polarization curve measurements revealed that the corrosion resistance of AZ31 treated by the immersion process improved considerably by the formation of superhydrophobic surfaces. The chemical durability of the superhydrophobic surfaces fabricated on AZ31 was also examined. The static water contact angle values for the superhydrophobic surfaces after immersion in aqueous solutions at pHs 4, 7, and 10 for 12 h were estimated to be 90 ± 2°, 119 ± 2°, and 138 ± 2°, respectively, demonstrating that their chemical durability in a basic solution was high.