Formation of nanostructured AlOOH film on Al alloys by steam coating toward corrosion protection

Al alloys have been used as advanced structural materials in automobile and railway industries because of excellent physical and mechanical properties such as low density, good heat conductivity, and high specific strength and... [ view full abstract ]

Al alloys have been used as advanced structural materials in automobile and railway industries because of excellent physical and mechanical properties such as low density, good heat conductivity, and high specific strength and ductility. Their low corrosion resistance, however, hinders their use in the corrosive environment. To improve the corrosion resistance of the Al alloys, the development of a novel coating technology has been highly desirable. In this presentation, we report a control method of corrosion protection for Al alloy using steam. The corrosion resistance of the composite film was also investigated.
Al-Mg-Si alloy was used as the substrate. The substrates were ultrasonically cleaned in absolute ethanol for 10 min. The cleaned Al-Mg-Si alloys were set in the autoclave. The cleaned Al-Mg-Si alloy substrates were introduced in a Teflon-lined autoclave with a 100 ml capacity. 20 ml of ultrapure water was located at the bottom of the autoclave to produce steam. The autoclave was heated to a temperature of 373 to 453 K, and then held at this temperature for up to 48 h, and was subsequently cooled naturally to room temperature, resulting in the formation of anticorrosive films on magnesium alloys. The resultant films were characterized by XRD, XPS, FE-SEM and electrochemical measurements.
FE-SEM image of film surface treated at 453 K for 48 h using steam were shown in Fig. 1. Plate-like nanostructure was densely formed on the surface. XRD patterns indicated that the film formed on two types of Al alloys by steam coating was mainly composed of crystal AlOOH. The corrosion resistance of the film was investigated using electrochemical measurements. The potentiodynamic polarization curves of the film coated and uncoated Al-Mg-Si alloy after immersion in the 5 wt% NaCl aqueous solution for 30 min revealed that the corrosion current density, jcorr, of the film coated Al-Mg-Si alloy decreased by more than two orders of magnitude as compared to the uncoated Al-Mg-Si alloy, indicating that the corrosion resistance of the Al-Mg-Si alloy were improved by the formation of the film via steam coating.
This work was supported by JSPS Grant-in-Aid for Young Scientists (B) Grant Number 15K18237.