Effect of Duty Cycle on Microstructure and Corrosion Resistance of MAO Coatings Fabricated on AZ91D Magnesium Alloy in an Optimized Dual Electrolyte

2013 ◽  
Vol 668 ◽  
pp. 779-783 ◽  
Author(s):  
Shu Yan Wang ◽  
Yong Ping Xia ◽  
Li Liu ◽  
Qiao Chen
Keyword(s):  
Surface Roughness ◽  
Corrosion Resistance ◽  
Phase Composition ◽  
Magnesium Alloy ◽  
Coating Thickness ◽  
Duty Cycle ◽  
Microarc Oxidation ◽  
Ceramic Coatings ◽  
Relative Content ◽  
Az91d Magnesium Alloy

Ceramic coatings were fabricated on AZ91D magnesium alloy in a novel optimized dual electrolyte by Microarc oxidation. The influence of duty cycle on coating thickness, surface roughness, phase composition, microstructure and corrosion resistance were studied. It is found that both the thickness and surface roughness of coatings increases gradually with the increasing of duty cycle. XRD results show that all the coatings are mainly composed of MgO, Mg2SiO4 and MgAl2O4. The results of potentiodynamic polarization tests indicate that the coating formed at 40% duty cycle exhibits a better corrosion resistance as a result of its relatively compact microstructure and more relative content of Mg2SiO4 and MgAl2O4 phases.

Effects of Sodium Citrate on MAO Process and Characteristics of Coatings Fabricated on AZ91D Magnesium Alloy

2012 ◽  
Vol 502 ◽  
pp. 320-324 ◽  
Author(s):  
Shu Yan Wang ◽  
Yong Ping Xia ◽  
Li Liu
Keyword(s):  
Surface Roughness ◽  
Corrosion Resistance ◽  
Magnesium Alloy ◽  
Sodium Citrate ◽  
Electrochemical Impedance ◽  
Microarc Oxidation ◽  
Dense Layer ◽  
Cross Sectional ◽  
Az91d Magnesium Alloy ◽  
Thickness Meter

Microarc oxidation (MAO) coatings were prepared on AZ91D magnesium alloy in a novel dual electrolyte containing various concentrations of sodium citrate (C6H5Na3O7). The surface and cross-sectional morphologies, coating thickness and surface roughness were characterized by scanning electron microscopy (SEM), layer thickness meter and digital microscope, respectively. The corrosion resistance of coatings was evaluated by electrochemical impedance spectroscopy (EIS). The results showed that both the striking voltage and final voltage decreased gradually with the increase of C6H5Na3O7 concentration. When the C6H5Na3O7 concentration increased, surface roughness increased gradually, while thickness of the coating increased at first and then decreased. The coating formed in the electrolyte containing 5g/L C6H5Na3O7 had a much more uniform and compact microstructure with less micropores and micro-cracks. EIS test showed that the concentration of C6H5Na3O7 mainly affected the corrosion resistance of inner dense layer, and the coating with best corrosion resistance was obtained in the electrolyte containing 5g/L C6H5Na3O7.

scholarly journals Corrosion resistance of the microarc oxidation coatings prepared on magnesium alloy

2018 ◽  
Vol 38 ◽  
pp. 02009
Author(s):  
Ying Lv ◽  
Jun Gang Li ◽  
Ming Zhong Wu ◽  
Zhen Ma ◽  
Jing Qiang Zhang ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Magnesium Alloy ◽  
Microarc Oxidation ◽  
Electrochemical Corrosion ◽  
Ceramic Coatings ◽  
Nacl Solution ◽  
Oxide Coatings ◽  
Az91d Magnesium Alloy ◽  
Oxidation Technology ◽  
Electrochemical Corrosion Resistance

Ceramic coatings were prepared on the surface of AZ91D magnesium alloy by microarc oxidation technology. The effects of different voltages on morphology, phase composition and thickness of the coatings were characterized by SEM and XRD. The corrosion resistance of the coatings was measured by electrochemical workstation. Results indicated that the microarc oxidation coatings prepared in sodium silicate electrolyte exhibited porous surface and mainly comprised MgO, Mg2SiO4 and a small amount of MgAl2O4. The thickness of the oxide coatings increased rapidly with the increase of voltage. The coating prepared at 400V voltage had good electrochemical corrosion resistance in 3.5wt% NaCl solution.

scholarly journals The effect of electrolysis conditions during microarc oxidation on the phase-structural state, hardness and corrosion resistance of magnesium alloys

2020 ◽  
Vol 21 (3) ◽  
pp. 545-551
Author(s):  
V.V. Subbotina ◽  
V.V. Belozerov
Keyword(s):  
Corrosion Resistance ◽  
Phase Composition ◽  
Magnesium Alloys ◽  
Protective Coatings ◽  
Microarc Oxidation ◽  
High Hardness ◽  
Ceramic Coatings ◽  
Functional Layer ◽  
Different Types ◽  
Spinel Mgal2o4

By the method of microarc oxidation for different types of electrolytes (which include KOH, Na2SiO3, Н2О2, NaOH, NaAlO2, Na5P3O10, NaF) and electrolysis conditions, multifunctional ceramic coatings on a magnesium alloy were obtained. The phase composition of the coating includes magnesium oxide (MgO), spinel MgAl2O4, Mg2SiO4 and Мg3(РО4)2 compounds. The phase composition of the coatings is determined by the composition of the electrolyte. The obtained MAO coatings provide high hardness, which is 1500 to 7300 MPa, as well as high corrosion resistance. The results obtained make it possible to recommend MAO coatings on magnesium alloys both as an external (functional) layer and for the formation of an underlayer for the subsequent application of protective coatings (varnishes, polymers, polytetrafluoroethylene, in particular).

Effect of Niobium Film on Corrosion Resistance of AZ91D Magnesium Alloy

2012 ◽  
Vol 525-526 ◽  
pp. 9-12 ◽  
Author(s):  
Er Bao Liu ◽  
Xiu Fang Cui ◽  
Guo Jin ◽  
Qing Fen Li ◽  
Tian Min Shao
Keyword(s):  
Corrosion Resistance ◽  
Elastic Modulus ◽  
Magnesium Alloy ◽  
Substrate Temperature ◽  
Phase Structure ◽  
Film Deposition ◽  
Negative Bias ◽  
Az91d Magnesium Alloy ◽  
Atomic Force ◽  
Deposition Parameters

The niobium film is prepared by magnetron sputtering on the surface of the AZ91D magnesium alloy. The morphology, phase structure, roughness, nanohardness and elastic modulus of the niobium films were studied by filed emission scanning electron microscope, X-ray diffraction, atomic force microscope and nanoindentation respectively. The influences of film deposition parameters, such as substrate temperature, negative bias and power on the properties of films were investigated. The corrosion resistance of niobium films on magnesium alloy was investigated by electrochemical system. Results show that the microstructure, phase structure, roughness, nanohardness and elastic modulus of the niobium films are determined by power, negative bias and substrate temperature. And the corrosion resistance of magnesium alloy improved obviously when coated with the niobium films.

Research on Corrosion Resistance of AZ91D Magnesium Alloy Coated with Epoxy Resin

2011 ◽  
Vol 686 ◽  
pp. 292-299
Author(s):  
Yong Gang Li ◽  
Ying Hui Wei ◽  
Li Feng Hou ◽  
Yun Tian ◽  
Li Jing Yang
Keyword(s):  
Corrosion Resistance ◽  
Magnesium Alloy ◽  
Adhesion Force ◽  
Die Casting ◽  
Corrosion Current ◽  
Scratch Test ◽  
Organic Coating ◽  
Thin Wall ◽  
Scanning Method ◽  
Az91d Magnesium Alloy

The corrosion resistance of a 1~2mm thick AZ91D magnesium alloy die-casting coated with epoxy varnish after phosphatizing was tested. Zinc phosphating solution was used. In the experiment, uniform paint was obtained by dipping method. Scratch test showed that the adhesion force between the coating and matrix is excellent. Within the test range the optimal phosphating temperature and time are 50°C and 1 min tested by dynamic potential scanning method. With the organic coating the corrosion current density decreased 3 orders of magnitude, the polarization resistance increased 3 orders of magnitude. The coated specimens were immersed in10% H2SO4, 10% NaOH and acetone for 10 days, respectively. The results showed that blistering did not occur on the paint films. This work illustrated that the simple zinc phosphating process combined with simple organic coating can meet the corrosion resistance requirements of thin-wall die casting magnesium components that require higher quality appearance.

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