Study of high emittance chemical conversion coatings for magnesium alloys

Abstract

omparative studies on five black chemical conversion coatings for magnesium alloy ZK60A have been conducted. The surface morphology and composition of the coatings were examined by SEM and energy dispersive spectroscopy techniques. The electrochemical and damp heat tests were conducted to examine the resistance of the coatings to corrosive prelaunch and launch conditions. The hemispherical emittance was measured to evaluate their worthiness of the application in aerospace industry. An optimum process condition, which provided a coating with satisfactory corrosion resistance and hemispherical emittance of 0-92, was determined. The formation mechanism and influence factors on the properties of the coatings were also discussed.

Preparation of chemical conversion super-black films on ZK61M magnesium alloy

“…This not only produced a large amount of hydrogen bubbles but also resulted in an increasing tendency for stress. In the subsequent formation process of the conversion film, the reactions between the substrate and solution also produced hydrogen, thus accounting for the formation of cracks [13]. The conversion film produced by process 1 was powdery and not sufficiently smooth, because the pH value in the process was too low to cause an intense reaction and a large amount of corrosion products.…”

“…Unfortunately, magnesium alloys have many disadvantages, such as poor corrosion, wear, and creep resistance, which restricts their applications [9][10][11]. Of these disadvantages, poor corrosion resistance is the main problem for outdoor applications [12][13][14]. In response, surface modification has been proposed as an effective means of degradation control of magnesium alloys.…”

Investigation of microcracks on conversion film of AZ80 Mg alloy

“…Many types of conversion films have already been developed to improve the corrosion resistance of Mg alloys [4][5][6]. However, abundant network cracks are observed on the surface of these conversion films, such as the Ce-V conversion film [7], phosphate conversion film [8], phosphate-permanganate conversion film [9], phytic acid conversion film [10].…”