Chrome-free surface treatments for magnesium alloy

Umehara, Hiroyuki; Takaya, Matsufumi; Terauchi, S.

doi:10.1016/s0257-8972(03)00052-5

Cited by 126 publications

(53 citation statements)

References 9 publications

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“…Apparent net-like cracks could be found on the coating surface when the amplification was 5000, while if the amplification decreased to 1000, the cracks could hardly be observed. Compared with the result of Umehara et al [4] and Kwo Zong Chong et al [5], the coatings obtained in this study were more compact. Moreover, in order to investigate the formation period of the cracks in the coating, the magnesium alloy plate, which was only treated by prior surface treatment, was observed by SEM (Fig.…”

Section: Morphology Of the Coatingscontrasting

confidence: 79%

“…Actually, many researchers have developed more environmentally friendly alternatives, such as permanganate bath, phosphate-permanganate bath, stannate bath and rare earth metal salts (REMS) bath [3][4][5][6][7][8]. Because of the similarity of permanganate to chromate, permanganate bath has the potential to replace chromate as the most suitable method applied to magnesium alloys.…”

Section: Introductionmentioning

confidence: 99%

“…Because of the similarity of permanganate to chromate, permanganate bath has the potential to replace chromate as the most suitable method applied to magnesium alloys. Early works done by Umehara and Takaya et al included permanganate bath incorporated with HNO 3 or HF as the constituents for the conversion treatment of magnesium alloys, but the corrosion resistance of the magnesium alloy treated by this bath was not adequate [5]. In recent years, some researchers have demonstrated that treatments with aqueous solutions of REMS, especially cerium salts, effectively inhibited the corrosion of metals [9][10][11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

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Conversion coating treatment for AZ91 magnesium alloys by a permanganate‐REMS bath

Liang

Zheng

2007

Materials & Corrosion

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A permanganate-rare earth metal salt (REMS) chemical conversion bath was applied to a sample of AZ91 magnesium alloy in this study, a red-brown conversion coating formed subsequently on the sample surface. The test results of this coating with a scanning electron microscope (SEM) showed that there existed net-like cracks on the surface of the treated magnesium alloy. With the analyses of Xray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS), a further study of this coating indicated that the coating was structurally amorphous and mainly composed of CeO 2 , MnO, MnO 2 , MgO, Mg(OH) 2 and MgAl 2 O 4 . Furthermore, the electrochemical polarization tests showed that compared with the samples treated by the chrome-based method, the open-circuit potential of the magnesium alloy coated in permanganate-REMS bath moved from À 1.34 V SCE to À 1.28 V SCE and the anodic current density of the alloy, at the same potential, decreased evidently in simulated sweat fluid. The cracks in the chemical conversion coating should be caused by the phase structure of the magnesium alloy. During the chemical conversion process, the localized corrosion micro-cell led to the formation of the net-like cracks on the surface. Simultaneously, the dehydration of the surface coating after treatment also accelerated the formation of the cracks at the coating surface.

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Section: Morphology Of the Coatingscontrasting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Conversion coating treatment for AZ91 magnesium alloys by a permanganate‐REMS bath

Liang

Zheng

2007

Materials & Corrosion

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“…Surface treatments can improve the corrosion resistance of magnesium and its alloys, which have been extensive researched in recently years [4]. In the surface treatment methods, Chemical conversion treatment is an effective and simple method, such as chromate [5], permanganate [6], phosphate [7,8], phosphate/permanganate [9,10], etc. Chromate conversion treatment as a conventional chemical conversion method, it has been widely used in industry for long time.…”

Section: Introductionmentioning

confidence: 99%

Formation process and properties of phytic acid conversion coatings on magnesium

Liu

Guo

Huang

2012

Anti-Corrosion Methods and Materials

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“…There were limit reports of phosphate coatings on magnesium alloys. Phosphate films were gained from phosphate-permanganate bath, which have micro cracks, [18][19][20] similar microstructure to chromate conversion. Recently, a zinc phosphate (Zn 3 (PO 4 ) 2 ·4H 2 O) coating was obtained on AM 60 magnesium alloy.…”

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confidence: 99%

Influence of pH of Phosphating Bath on the Zinc Phosphate Coating on AZ91D Magnesium Alloy

Lian

Niu

et al. 2006

Adv Eng Mater

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Magnesium alloy has some advantageous properties including low density and high strength to weight ratio, [1] high thermal conductivity, good electromagnetic features and being easily recycled. These properties make it valuable in a number of industrial fields including automobile, aerospace components, mobile phones and sporting goods. [2][3][4][5][6][7] For example, the use of magnesium alloys can significantly decrease the weight of automobiles without sacrificing structural strength.When magnesium alloys are exposed to the atmosphere, their surfaces form a kind of film consisting magnesium oxide and magnesium hydroxide that gives limited protection from further attack. The film has no the same self-healing property as the film of aluminum alloy that formed in atmospheres. In reverse, chlorides, sulfates, or other hydrophilic substances promote corrosion by destroying this film easily. Unfortunately, this poor corrosion resistance of magnesium alloys has hindered their widely applications where exposure to rigorous service conditions is unavoidable.More interest was paid to the investigations of corrosion of magnesium alloy in recent years. [8][9][10][11] Anticorrosion properties of magnesium alloy can be improved by application high-purity alloys and surface protection. Producers of magnesium have demonstrated the importance of high-purity alloys for structural applications. However, surface contamination from handling and mechanical treatment can greatly degrade the corrosion resistance of high-purity alloys. One of the most effective ways to prevent corrosion is to coat the base materials. Some surface protection reports of magnesium alloy were published including electroplating Ni-P, [12] chromate conversion coating, [13] Zn-Ni alloy coating, [14] anodizing film, [15,16] and plasma surface treatment film. [17] Among these possible treatment, zinc phosphatization may be one of the most promising methods for magnesium alloy anticorrosion and pretreatment process before paint. Especially, it has the potential to replace the conventional chromate treatment where the environment polluted hexad chromium was involved. There were limit reports of phosphate coatings on magnesium alloys. Phosphate films were gained from phosphate-permanganate bath, which have micro cracks, [18][19][20] similar microstructure to chromate conversion. Recently, a zinc phosphate (Zn 3 (PO 4 ) 2 ·4H 2 O) coating was obtained on AM 60 magnesium alloy. [21] Han et al. obtained a phosphate film of Mn 3 (PO 4 ) 2 on AZ31D magnesium alloy in a bath containing phosphate and manganese. [22] In a previous work, a phosphate coating with the compositions in the coating being Zn 3 (PO 4 ) 2 ·4H 2 O, metal Zn and AlPO 4 was obtained. [23] In fact, phosphatization of magnesium alloy is very different and rather difficult in comparison with the traditional phosphatization of steel and aluminum because of high electrochemically activity of magnesium. In the acid phosphating bath resolving rate of magnesium must be restrained in order to obtain dense a...

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Chrome-free surface treatments for magnesium alloy

Cited by 126 publications

References 9 publications

Conversion coating treatment for AZ91 magnesium alloys by a permanganate‐REMS bath

Conversion coating treatment for AZ91 magnesium alloys by a permanganate‐REMS bath

Formation process and properties of phytic acid conversion coatings on magnesium

Influence of pH of Phosphating Bath on the Zinc Phosphate Coating on AZ91D Magnesium Alloy

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