Crack self-healing of phytic acid conversion coating on AZ31 magnesium alloy by heat treatment and the corrosion resistance

AZ91 magnesium alloy is selected as the matrix metal. SEM, EDS, Tafel and EIS were adopted and spot test was carried out to investigate the influence of pH value, phytic acid concentration, temperature,conversion time on corrosion resistance of conversion coatings. Result shows that process of phytic acid forming is the controlled metal corrosion process and the uneven surface pattern reflects the different chemical properties of two-phase current on magnesium alloy surface, which is implied by the conversion surface. It is proved by the test that pH value is committed the most to the corrosion resistance of the conversion coating, and the next is the phytic acid concentration. It is found that the corrosion resistance of the conversion coating is the best when pH value of the conversion solution is 4.5; The conversion coating has little influence on the cathode reaction dynamics, however, more importantly, it changes the dynamics of the alloy electrode anode solution reaction, therefore, the alloy’s anode current density decreases while the corrosion resistance of magnesium alloy is enhanced.

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Optimization of process factors for self-healing vanadium-based conversion coating on AZ31 magnesium alloy

Applied Surface Science ◽

10.1016/j.apsusc.2015.07.052 ◽

2015 ◽

Vol 353 ◽

pp. 811-819 ◽

Cited By ~ 26

Author(s):

Kun Li ◽

Junyao Liu ◽

Ting Lei ◽

Tao Xiao

Keyword(s):

Magnesium Alloy ◽

Conversion Coating ◽

Az31 Magnesium Alloy ◽

Self Healing ◽

Process Factors

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A simple method for the preparation of magnesium phosphate conversion coatings on a AZ31 magnesium alloy with improved corrosion resistance

RSC Advances ◽

10.1039/c5ra00329f ◽

2015 ◽

Vol 5 (31) ◽

pp. 24586-24590 ◽

Cited By ~ 27

Author(s):

Huan Zhao ◽

Shu Cai ◽

Zetao Ding ◽

Ming Zhang ◽

Yan Li ◽

...

Keyword(s):

Corrosion Resistance ◽

Magnesium Alloy ◽

Conversion Coating ◽

Az31 Magnesium Alloy ◽

Magnesium Phosphate ◽

Conversion Coatings ◽

Simple Method ◽

Alloy Az31 ◽

Magnesium Alloy Az31

A simple method has been proposed for the preparation of magnesium phosphate conversion coating on a magnesium alloy (AZ31) to achieve protection against fast degradation in an implant environment.

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Microstructure and corrosion resistance of Ce–V conversion coating on AZ31 magnesium alloy

Applied Surface Science ◽

10.1016/j.apsusc.2015.02.195 ◽

2015 ◽

Vol 341 ◽

pp. 166-174 ◽

Cited By ~ 39

Author(s):

Xiao Jiang ◽

Ruiguang Guo ◽

Shuqin Jiang

Keyword(s):

Corrosion Resistance ◽

Magnesium Alloy ◽

Conversion Coating ◽

Az31 Magnesium Alloy

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Characterization and Corrosion Properties of Fluoride Conversion Coating Prepared on AZ31 Magnesium Alloy

Coatings ◽

10.3390/coatings11060675 ◽

2021 ◽

Vol 11 (6) ◽

pp. 675

Author(s):

Juliána Dziková ◽

Stanislava Fintová ◽

Daniel Kajánek ◽

Zuzana Florková ◽

Jaromír Wasserbauer ◽

...

Keyword(s):

Corrosion Resistance ◽

Magnesium Alloy ◽

Molten Salt ◽

Electrochemical Impedance ◽

Intermetallic Phase ◽

Negative Influence ◽

Conversion Coating ◽

Az31 Magnesium Alloy ◽

Corrosion Properties ◽

Coating Temperature

Wrought AZ31 magnesium alloy was used as the experimental material for fluoride conversion coating preparation in Na[BF4] molten salt. Two coating temperatures, 430 °C and 450 °C, and three coating times, 0.5, 2, and 8 h, were used for the coating preparation. A scanning electron microscope and energy-dispersive X-ray spectroscopy were used for an investigation of the surface morphology and the cross-sections of the prepared coatings including chemical composition determination. The corrosion resistance of the prepared specimens was investigated in terms of the potentiodynamic tests, electrochemical impedance spectroscopy and immersion tests in the environment of simulated body fluids at 37 ± 2 °C. The increase in the coating temperature and coating time resulted in higher coatings thicknesses and better corrosion resistance. Higher coating temperature was accompanied by smaller defects uniformly distributed on the coating surface. The defects were most probably created due to the reaction of the AlxMny intermetallic phase with Na[BF4] molten salt and/or with the product of its decomposition, BF3 compound, resulting in the creation of soluble Na3[AlF6] and AlF3 compounds, which were removed from the coating during the removal of the secondary Na[MgF3] layer. The negative influence of the AlxMny intermetallic phase was correlated to the particle size and thus the size of created defects.

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