A Chromate-Free and Convenient Route to Fabricate Thin and Compact Conversion Coating for Corrosion Protection on LZ91 Magnesium Alloy

This study characterizes and determines the corrosion resistance of Mn-Ce conversion coated LZ91 magnesium alloy that undergoes pretreatments. It is challenging to process large and curved workpieces in the industry because the geometric shapes are complex if they are mechanically ground. This study...

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Main Authors: Chun-Wei Chen, Salim Levent Aktug, Chin-Jou Chang, Yueh-Lien Lee, Ming-Der Ger, Shun-Yi Jian
Format: Article
Language:English
Published: MDPI AG 2022-05-01
Series:Nanomaterials
Subjects:
Online Access:https://www.mdpi.com/2079-4991/12/9/1614
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author Chun-Wei Chen
Salim Levent Aktug
Chin-Jou Chang
Yueh-Lien Lee
Ming-Der Ger
Shun-Yi Jian
author_facet Chun-Wei Chen
Salim Levent Aktug
Chin-Jou Chang
Yueh-Lien Lee
Ming-Der Ger
Shun-Yi Jian
author_sort Chun-Wei Chen
collection DOAJ
description This study characterizes and determines the corrosion resistance of Mn-Ce conversion coated LZ91 magnesium alloy that undergoes pretreatments. It is challenging to process large and curved workpieces in the industry because the geometric shapes are complex if they are mechanically ground. This study uses acid pickling instead of mechanical grinding, and a nitric acid solution is used for pickling. After pretreatments, the samples are immersed for 30 s in a conversion coating solution containing 0.1 M KMnO<sub>4</sub> and 0.025 M Ce(NO<sub>3</sub>)<sub>3</sub> with a pH of 1.5, as demonstrated in previous studies by the authors. The microstructure of the coating layer and electrochemical behavior of conversion coated samples exposed to 3.5 wt.% NaCl solution are studied. The corrosion behavior of Mn-Ce conversion coating specimens is determined using a salt spray test (SST). Scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) are used to analyze the interface between the coating layer and the underlying magnesium substrate and to investigate the microstructure of the specimens. The roughness of the coatings is measured using 3D white light interferometry. The results show that the deteriorated area ratio for conversion coated LZ91 decreases to less than 5% after 72 h of SST exposure, and the corrosion resistance is improved 2.25 times with the Mn-Ce conversion coating on LZ91 magnesium alloy.
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spelling doaj.art-dfb430b33fbb4f5cadd5c879352bedde2023-11-23T08:56:54ZengMDPI AGNanomaterials2079-49912022-05-01129161410.3390/nano12091614A Chromate-Free and Convenient Route to Fabricate Thin and Compact Conversion Coating for Corrosion Protection on LZ91 Magnesium AlloyChun-Wei Chen0Salim Levent Aktug1Chin-Jou Chang2Yueh-Lien Lee3Ming-Der Ger4Shun-Yi Jian5Department of Chemical & Materials Engineering, Chung Cheng Institute of Technology, National Defense University, Taoyuan 33551, TaiwanDepartment of Materials Science and Engineering, Gebze Technical University, Gebze 41400, Kocaeli, TurkeyDepartment of Chemical & Materials Engineering, Chung Cheng Institute of Technology, National Defense University, Taoyuan 33551, TaiwanDepartment of Engineering Science and Ocean Engineering, National Taiwan University, Taipei 10617, TaiwanDepartment of Chemical & Materials Engineering, Chung Cheng Institute of Technology, National Defense University, Taoyuan 33551, TaiwanDepartment of Material Engineering, Ming Chi University of Technology, New Taipei City 24301, TaiwanThis study characterizes and determines the corrosion resistance of Mn-Ce conversion coated LZ91 magnesium alloy that undergoes pretreatments. It is challenging to process large and curved workpieces in the industry because the geometric shapes are complex if they are mechanically ground. This study uses acid pickling instead of mechanical grinding, and a nitric acid solution is used for pickling. After pretreatments, the samples are immersed for 30 s in a conversion coating solution containing 0.1 M KMnO<sub>4</sub> and 0.025 M Ce(NO<sub>3</sub>)<sub>3</sub> with a pH of 1.5, as demonstrated in previous studies by the authors. The microstructure of the coating layer and electrochemical behavior of conversion coated samples exposed to 3.5 wt.% NaCl solution are studied. The corrosion behavior of Mn-Ce conversion coating specimens is determined using a salt spray test (SST). Scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) are used to analyze the interface between the coating layer and the underlying magnesium substrate and to investigate the microstructure of the specimens. The roughness of the coatings is measured using 3D white light interferometry. The results show that the deteriorated area ratio for conversion coated LZ91 decreases to less than 5% after 72 h of SST exposure, and the corrosion resistance is improved 2.25 times with the Mn-Ce conversion coating on LZ91 magnesium alloy.https://www.mdpi.com/2079-4991/12/9/1614LZ91 magnesium alloyacid pickling pretreatmentconversion coatingmicrostructurecorrosion resistance
spellingShingle Chun-Wei Chen
Salim Levent Aktug
Chin-Jou Chang
Yueh-Lien Lee
Ming-Der Ger
Shun-Yi Jian
A Chromate-Free and Convenient Route to Fabricate Thin and Compact Conversion Coating for Corrosion Protection on LZ91 Magnesium Alloy
Nanomaterials
LZ91 magnesium alloy
acid pickling pretreatment
conversion coating
microstructure
corrosion resistance
title A Chromate-Free and Convenient Route to Fabricate Thin and Compact Conversion Coating for Corrosion Protection on LZ91 Magnesium Alloy
title_full A Chromate-Free and Convenient Route to Fabricate Thin and Compact Conversion Coating for Corrosion Protection on LZ91 Magnesium Alloy
title_fullStr A Chromate-Free and Convenient Route to Fabricate Thin and Compact Conversion Coating for Corrosion Protection on LZ91 Magnesium Alloy
title_full_unstemmed A Chromate-Free and Convenient Route to Fabricate Thin and Compact Conversion Coating for Corrosion Protection on LZ91 Magnesium Alloy
title_short A Chromate-Free and Convenient Route to Fabricate Thin and Compact Conversion Coating for Corrosion Protection on LZ91 Magnesium Alloy
title_sort chromate free and convenient route to fabricate thin and compact conversion coating for corrosion protection on lz91 magnesium alloy
topic LZ91 magnesium alloy
acid pickling pretreatment
conversion coating
microstructure
corrosion resistance
url https://www.mdpi.com/2079-4991/12/9/1614
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