The one-step preparation and corrosion resistance of a Ca–Mn–Zn ternary phosphate conversion coating on magnesium alloy AZ91D
Anti-Corrosion Methods and Materials
ISSN: 0003-5599
Article publication date: 18 April 2022
Issue publication date: 3 June 2022
Abstract
Purpose
The aim of this work was to propose a method to prepare composite phosphate conversion coating (CPCC), including ternary phosphate conversion coating (TPCC) and binary phosphate conversion coatings (BPCC), with one-step chemical conversion and to reveal and compare the corrosion resistance between TPCC and BPCC.
Design/methodology/approach
In this work, a calcium–manganese–zinc (Ca–Mn–Zn) TPCC was prepared on the surface of magnesium alloy (MA) AZ91D with one-step chemical conversion method; for Ca-Mn-Zn@TPCC, its microstructure was characterized with scanning electron microscope observation and scanning tunneling microscope detection, and its composition was characterized with energy dispersion spectroscopy and X-ray photoelectron spectroscopy analyses. Particularly, the corrosion resistance of Ca-Mn-Zn@TPCC and its comparison with Ca–Mn, Ca–Zn and Mn–Zn BPCCs were clarified with electrochemical and immersion measurements.
Findings
Ca-Mn-Zn@TPCC, which was composed of Ca, Mn, Zn, P and O, exhibited a mud-shaped with cracks microstructure, and the average crack width, terrain fluctuation and coating thickness were 0.61 µm, 23.78 nm and 2.47 µm, respectively. Ca-Mn-Zn@TPCC provided good corrosion resistance to MA AZ91D; in NaCl solution, the total degradation of Ca-Mn-Zn@TPCC consumed eight days; corrosion products with poor adhesion peeled out from Ca-Mn-Zn@TPCC-coated MA AZ91D spontaneously. Besides, the corrosion resistance of Ca-Mn-Zn@TPCC was better than that of Ca-Mn@BPCC, Ca-Zn@BPCC or Mn-Zn@BPCC.
Originality/value
The successful preparation of Ca-Mn-Zn@TPCC on MA AZ91D surface confirmed the proposed method to prepare CPCC with one-step chemical conversion was feasible; at the same time, it was further confirmed that for phosphate conversion coating, ternary coating had better corrosion resistance than binary coating did.
Keywords
Acknowledgements
This work is supported by the National Natural Science Foundation of China (51601133) and the open fund of Beijing Key Laboratory of Quality Evaluation Technology for Hygiene and Safety of Plastic (QETHSP2021009).
Citation
Yang, J., Zhang, P., Su, L., Yan, F. and Yong, Z. (2022), "The one-step preparation and corrosion resistance of a Ca–Mn–Zn ternary phosphate conversion coating on magnesium alloy AZ91D", Anti-Corrosion Methods and Materials, Vol. 69 No. 4, pp. 341-350. https://doi.org/10.1108/ACMM-08-2021-2531
Publisher
:Emerald Publishing Limited
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