Effect of (NH4)2ZrF6, Voltage and Treating Time on Corrosion Resistance of Micro-Arc Oxidation Coatings Applied on ZK61M Magnesium Alloys.

Jiahui Yong,Yongnan Chen,Hongzhan Li,Zhengxian Li,Juanjuan Geng,Yifei Wang

doi:10.3390/ma14237410

Abstract

The effects of (NH4)2ZrF6 concentration, voltage and treating time on the corrosion resistance of ZK61M magnesium alloy micro-arc oxidation coatings were studied by orthogonal experiments. The SEM result shows that the surface roughness and porosity of MAO coatings increased with (NH4)2ZrF6 concentration, voltage and treating time as a whole, except the porosity decreased with treating time. EDS, XRD and XPS analysis show that (NH4)2ZrF6 was successfully incorporated into coatings by reactive incorporation, coatings are dominantly composed of ZrO2, MgO, MgF2 and amorphous phase Mg phosphate. Potentiodynamic polarization was used to evaluate the corrosion property of coatings. When the concentration of (NH4)2ZrF6 is 6 g/L, the voltage is 450 V, and the treating time is 15 min, the coating exhibits the best corrosion resistance which corrosion current density is four magnitudes lower than substrate attributed to the incorporation of ZrO2 and the deposition of MgF2 in the micropores.

Highlights

Magnesium alloys are the lightest structural metallic materials, which are widely used in aerospace, automotive, 3C electronic products, biomedical applications due to their high specific strength, high specific stiffness, excellent shock absorption performance and electromagnetic shielding performance, good machinability, biocompatibility [1,2]
Micro-arc oxidation (MAO) is a surface modification method developed from conventional anodic oxidation; it can generate a well-adhered oxide ceramic coating on the surface of magnesium alloy; the magnesium substrate can be effectively protected
Corrosion current density (Icorr), surface roughness (Ra) abstracted from AFM (Figure 1) and porosity were used as measures of coating quality, the corresponding samples were named 1#, 2#, 3#, 4#, 5#, 6#, 7#, 8#, 9#. k1 and k2 represent the mean values of the corresponding level of each factor, R stands for extremely poor, and its value is proportional to the importance of the coatings

Summary

Introduction

Magnesium alloys are the lightest structural metallic materials, which are widely used in aerospace, automotive, 3C electronic products, biomedical applications due to their high specific strength, high specific stiffness, excellent shock absorption performance and electromagnetic shielding performance, good machinability, biocompatibility [1,2]. Micro-arc oxidation (MAO) is a surface modification method developed from conventional anodic oxidation; it can generate a well-adhered oxide ceramic coating on the surface of magnesium alloy; the magnesium substrate can be effectively protected. In the MAO process, the substrate that as an anode is put into the electrolyte which we prepared, apply a high voltage, there will be plasma discharge and the surface of the sample converts the metallic substrate into an oxide coating [7]. It is well known that the MAO tratement is very complex, which involves chemical, electrochemical, thermochemical, plasma chemical, metallurgical processes [8,9]

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