Recent Studies on Coating of some Magnesium Alloys; Anodizing, Electroless Coating and Hot Press Cladding

In the present study, coating of some magnesium alloys including AZ31 and AZ91 were studied using different techniques namely anodizing, electroless and hot press cladding. AZ91 alloy was coated using anodizing process using three types of environmental friendly electrolytes; the first based on sodium silicate, the second based on sodium hydroxide-boric acid-borax and the third on sodium silicate-potassium hydroxide-sodium carbonate-sodium tetra borate. Characterization of the anodizing layer was achieved by determination of surface morphology, microstructure, phase analysis, coat thickness, adhesion and corrosion resistance. It was found that the anodic film thickness increases with increasing the current density, anodizing voltage and deposition time until the deposition stops due to the formation of a thick anodic film. The range of the anodic film thickness is 28 42 µm.Optimization of the anodizing conditions - current density and deposition time was determined for each electrolyte. A corrosion efficiency ranging from 94% to 97% was reached; the highest value corresponding to the third electrolyte. Another study is the electroless Ni plating technique with zinc pre-treatment applied on several magnesium alloys and the effect of pre-treatment and post heat treatment on the coat characteristics. The surface morphology, surface roughness, thickness of the layer, EDX analysis, adhesion, hardness and corrosion resistance are covered in this part. The electroless layer thickness is about 6 µm. The results showed good bond quality of the coat maintaining good corrosion behaviour of electroless Ni-P based on potentiodynamic polarization tests in chloride solution where it was improved after heat treatment process. On the other hand, AZ31 was covered by a commercial pure aluminum sheet by hot pressing. The influence of the applied pressure, holding time and temperature on the bond characteristics was studied. The experimental investigation has revealed a good bond quality due to the effective mutual diffusion of Mg and Al. The phase analysis resulted in the formation of two equilibrium phases namely; Mg17Al12and Mg2Al3. The corrosion resistance of AZ31 is enhanced as a results of this process by 98.6%. Further points will be covered.Keywords: Magnesium alloys; Coating; Anodizing; Electroless; Hot press cladding; environmental friendly electrolytes; corrosion

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Fast Electroless Ni-P Coating on AM60 Magnesium Alloy at Low Bath Temperature

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.418-420.756 ◽

2011 ◽

Vol 418-420 ◽

pp. 756-759 ◽

Cited By ~ 1

Author(s):

Guo Bing Mao

Keyword(s):

Growth Rate ◽

Corrosion Resistance ◽

Magnesium Alloy ◽

Magnesium Alloys ◽

Electroless Plating ◽

Corrosion Test ◽

Bath Temperature ◽

Test Results ◽

Electroless Ni

The Ni-P coatings were deposited on AM60 magnesium alloy by electroless plating process without or with accelerators. Without accelerators, the deposition rate is slow and required high bath temperature to obtain compact coating. There have many defects on the surface of the Ni-P coatings which deposited at high bath temperature. The composite accelerators were introduced into the bath for improving the growth rate and the quality of the Ni-P coating. Uniform, with no pores or cracks, “cauliflower-like” structure and complete Ni-P coatings were deposited only taken 20 min with additives at low bath temperature. The XRD result indicates that the structure of the Ni-P coating is amorphous nickel. The corrosion test results indicated that the corrosion resistance of this coated AM60 magnesium alloys increases distinctly as compared to bare alloys.

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Surface Treatment of Magnesium Alloys by Electroless Ni –P Plating Technique with Emphasis on Zinc Pre-Treatment: A Review

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.384.241 ◽

2008 ◽

Vol 384 ◽

pp. 241-262 ◽

Cited By ~ 6

Author(s):

Nahed El Mahallawy

Keyword(s):

Heat Treatment ◽

Surface Treatment ◽

Magnesium Alloys ◽

Industrial Applications ◽

Harsh Environments ◽

Light Weight ◽

Post Heat Treatment ◽

Plating Technique ◽

Pre Treatment ◽

Electroless Ni

Magnesium alloys are attractive alloys in industrial applications , where light weight and good strength structures are required. Magnesium alloys are versatile and include both cast and wrought alloys. However, they have a drawback as they are prone to corrosion especially in harsh environments. For this reason, surface treatment of magnesium alloys is of prime importance for improving their corrosion characteristics. In the present paper, a survey of the different methods for surface treatment of magnesium alloys is presented and discussed. This is followed by a review of the recent work on electroless Ni plating technique with zinc pre-treatment applied on several magnesium alloys and the effect of pretreatment and post heat treatment on the coat characteristics. The surface morphology, surface roughness, thickness of the layer, EDX analysis, adhesion, hardness and corrosion resistance are covered in this review.

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Effect of HCl pre-treatment on corrosion resistance of cerium-based conversion coatings on magnesium and magnesium alloys

Corrosion Science ◽

10.1016/j.corsci.2004.06.016 ◽

2005 ◽

Vol 47 (4) ◽

pp. 989-1000 ◽

Cited By ~ 177

Author(s):

Katya Brunelli ◽

Manuele Dabalà ◽

Irene Calliari ◽

Maurizio Magrini

Keyword(s):

Corrosion Resistance ◽

Magnesium Alloys ◽

Conversion Coatings ◽

Pre Treatment

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A study of corrosion resistance and formation characteristics of electroless Ni–P alloy coatings on Al18B4O33w/6061 Al composite with a simple surface pre-treatment

Surface and Coatings Technology ◽

10.1016/j.surfcoat.2010.05.047 ◽

2010 ◽

Vol 205 (1) ◽

pp. 43-49 ◽

Cited By ~ 12

Author(s):

Sha-wei Tang ◽

Cui-ju Wang ◽

Ya-Li Sun ◽

Jin Hu

Keyword(s):

Corrosion Resistance ◽

Al Composite ◽

Pre Treatment ◽

Electroless Ni ◽

Simple Surface

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Optimization of the Corrosion Resistance of Electroless Ni–W–P Coatings on Magnesium Alloys by the Response Surface Methodology

Coatings ◽

10.3390/coatings11010018 ◽

2020 ◽

Vol 11 (1) ◽

pp. 18

Author(s):

Bin Liu ◽

Qing Zhang ◽

Yang Li ◽

Yuebo Yang ◽

Tao Zhang ◽

...

Keyword(s):

Response Surface Methodology ◽

Corrosion Resistance ◽

Response Surface ◽

Magnesium Alloys ◽

Sodium Tungstate ◽

Nickel Sulfate ◽

Bath Temperature ◽

Sodium Hypophosphite ◽

Technological Parameters ◽

Electroless Ni

Plating processes greatly affect the corrosion resistance of electroless Ni–W–P coatings on magnesium alloys. In the present research, the corrosion resistance of electroless Ni–W–P alloy-coated AZ91D magnesium alloy was optimized by the response surface methodology. The optimum technological parameters of the plating process were determined by establishing a quadratic regression model, and the influence of these variables and their interactions on the corrosion resistance of the coating was analyzed. The optimum technological parameters of the electroless plating process were nickel sulfate concentration = 20 g/L, sodium tungstate concentration = 15 g/L, sodium hypophosphite concentration = 30 g/L, bath temperature = 60 °C, and bath pH = 9.3. Under these conditions, the coating had the best corrosion resistance. Among the aforementioned five variables, sodium tungstate concentration had the most significant influence on the corrosion resistance of the coating. Different degrees of interactions among the variables greatly affected the corrosion resistance of the coating.

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A New Route for Direct Electroless Ni-P Plating on Magnesium Alloys

VNU Journal of Science Natural Sciences and Technology ◽

10.25073/2588-1140/vnunst.4507 ◽

2017 ◽

Vol 33 (2) ◽

Author(s):

Bùi Xuân Vương

Keyword(s):

Corrosion Resistance ◽

Magnesium Alloys ◽

Substrate Surface ◽

Nickel Sulfate ◽

Plating Bath ◽

High Adhesion ◽

Pickling Solution ◽

Salt Component ◽

Coarse Surface ◽

Electroless Ni

This report describes a new route for direct electroless Ni-P plating on magnesium alloys using nickel sulfate as the main salt component. The surface morphology, chemical composition and corrosion resistance of coatings were determined using SEM, EDX and electrochemical polarization techniques. Ni-P coatings with good corrosion resistance and high adhesion were obtained using this route and improved pretreatments. A mixture of H3PO4 and HNO3 was used as a pickling solution for Mg substrate pretreatment. A coarse surface was produced via the developed pickling procedure. A mechanical occlusive force is believed to exist between the coatings and the substrates. Twice activations, K4P2O7 and NH4HF2 as activation components, respectively, were applied for the pretreatment of magnesium alloy plating. An optimal F/O ratio on the Mg substrate surface was obtained by this pretreatment method. The activation film has insoluble partial fluorides which can depress the active points on substrate surface against the reaction of Mg with Ni2+ and H+ in the plating bath. A highly stable bath with pH 5 buffer was identified. The advantages of the developed process include chromium-free, low fluoride, and high bath stability. It is applicable for the production of motorcycle part plating.

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Effect of Heat Treatment of AZ91 Magnesium Alloy on the Electroless Ni-P Deposition

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1148.122 ◽

2018 ◽

Vol 1148 ◽

pp. 122-127 ◽

Cited By ~ 1

Author(s):

Charu Singh ◽

S.K. Tiwari ◽

Raghuvir Singh

Keyword(s):

Heat Treatment ◽

Corrosion Resistance ◽

Magnesium Alloy ◽

Magnesium Alloys ◽

Electrochemical Impedance ◽

Cast Alloy ◽

Az91 Magnesium Alloy ◽

Heat Treated ◽

Az91 Magnesium ◽

Electroless Ni

Magnesium alloys are excellent choice for automobile, aerospace, and computer components owing to their light weight, unique physical and mechanical properties. However, poor corrosion resistance has restricted their applications in aggressive environments. The surface coating is one of the viable options to reduce the susceptibility of magnesium alloys to corrosion. The present study focuses on the effect of heat treatment of AZ91 magnesium alloy, for different durations at 400 °C, prior to electroless Ni-P deposition on corrosion resistance. The microstructure and elemental analysis of the heat-treated specimens are performed using SEM and EDS techniques respectively. It is observed that the duration of heat treatment has a significant effect on the surface morphology and microstructure of the alloy. The precipitates in the cast alloy (enriched with Mg and Al) fragmented and the transformed into a new Al and Zn rich phase, after 12 h heat treatment. The dissolution of precipitates, however, observed on heating further to 24 h and exhibited relatively a lesser corrosion current density. The dense electroless Ni-P deposition is formed on the alloy heat treated for 24 h. The corrosion behavior of the single Ni-P layer on the heat treated (for 12 h) and untreated alloy show a marked deterioration, as investigated by the anodic polarization and electrochemical impedance spectroscopy (EIS) techniques. Relatively a better corrosion performance is seen for the double-layer Ni-P deposition. The duplex layer coatings on the as cast and heat treated for 24 h at 400 °C substrates showed an improved corrosion resistance compared to that on the 12 h heat treated substrate.

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Effect of Deposition Time on the Morphological Features and Corrosion Resistance of Electroless Ni-High P Coatings on Aluminium

Journal of Materials ◽

10.1155/2013/985763 ◽

2013 ◽

Vol 2013 ◽

pp. 1-7 ◽

Cited By ~ 4

Author(s):

N. Sridhar ◽

K. Udaya Bhat

Keyword(s):

Corrosion Resistance ◽

Electroless Deposition ◽

Deposition Time ◽

Substrate Material ◽

X Ray Diffraction ◽

X Ray ◽

Energy Dispersive Spectroscope ◽

Electroless Ni ◽

Limiting Value ◽

Scanning Electron

High phosphorus Ni-P alloy was deposited on aluminium substrate using electroless deposition route. Using zincating bath, the surface was activated before deposition. Deposition time was varied from 15 minutes to 3 hours. Deposit was characterised using scanning electron microscope with energy dispersive spectroscope, X-ray diffraction, and microhardness tester. The corrosion resistance was measured using Tafel extrapolation route. The medium was aqueous 5% HNO3 solution. The analysis showed that the deposit consisted of nodules of submicron and micron scale. The predominant phase in the deposit was nickel along with phosphides of nickel. Compared to substrate material, deposit showed higher hardness. With increase in deposition time, the deposit showed more nobleness in 5% HNO3 solution and nobleness reached a limiting value in 1 hour deposition time.

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