Abstract
The effect of temperature on the corrosion resistance of layered double hydroxide (LDH) conversion coatings on AZ91D magnesium alloy, based on a closed-cycle system, was investigated. Scanning electron microscopy (SEM), photoelectron spectroscopy (XPS), and X-ray diffractometry (GAXRD) were used to study the surface morphology, chemical composition, and phase composition of the conversion coating. The corrosion resistance of the LDH conversion coating was determined through electropotentiometric polarisation curve and hydrogen evolution and immersion tests. The results showed that the conversion coating has the highest density and a more uniform, complete, and effective corrosion resistance at 50 °C. The chemical composition of the LDH conversion coating mainly comprises C, O, Mg, and Al, and the main phase is Mg6Al2(OH)16CO3·4H2O.
Highlights
Magnesium alloys have been believed to be “the green engineering material of the 21st century”, and have met wide application prospects in automotive, aerospace, electronics, and biomedical fields [1,2]
The Mg-Al-hydrotalcite layered double hydroxide (LDH) coatings were prepared by the carbonate/bicarbonate solutions stand at 50 ◦C for 24 h, which was recorded as CO2_24h [41,42]
It was found that the precursor coating with cracks initially formed; LDH conversion coatings formed densely and compactly
Summary
Magnesium alloys have been believed to be “the green engineering material of the 21st century”, and have met wide application prospects in automotive, aerospace, electronics, and biomedical fields [1,2]. One of the most effective and convenient ways of improving the corrosion resistance of magnesium alloys [12,13,14]. The porous oxide/hydroxide coatings formed on the surface of magnesium alloys are not able to protect anti-corrosion. Common surface treatments of magnesium alloys include micro-arc/anodizing, electroplating/electroless plating, laser surface treatment, chemical conversion treatment, organic coating treatment, surface infiltration treatment, and ion implantation [21,22,23,24,25,26]. Uan et al [39,40] carried out some research on the hydrotalcite coatings prepared on magnesium alloys by the one-step method. Zhang et al [51,52] put forward the ion exchange and corrosion resistance properties by preparing MgAl-LDH coatings on Mg and Al alloys
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