Surface Of AZ91 Magnesium Alloy Research Articles

Effect of Laser Remelting of Fe-Based Thermally Sprayed Coating on AZ91 Magnesium Alloy on Its Structural and Tribological Properties

An Fe-based coating was thermally sprayed onto the surface of AZ91 magnesium alloy via the High-Velocity-Oxygen-Fuel (HVOF) method. The thermally sprayed coating with a thickness of 530 ± 25 µm and a porosity of 0.7 ± 0.1% did not show any macrostructural defects and did not cause any degradation of the AZ91 alloy. Laser remelting of the surface layer of the sprayed coating resulted in the recrystallization of the structure and the disappearance of presented pores, splat boundaries, and other defects. This led to an increase in the hardness of the remelted layer from the original 535 ± 20 HV0.3 up to 625 ± 5 HV0.3. However, during the laser remelting at a laser power of 1000 W, stress cracking in the coating occurred. The tribological properties were evaluated by the ball-on-plate method under dry conditions. Compared to the uncoated AZ91 magnesium alloy, a higher value of friction coefficient (COF) was measured for the as-sprayed coating. However, there was a decrease in wear rate and weight loss. The remelting of the surface layer of the as-sprayed coating led to a further decrease in the wear rate and weight loss. Based on the obtained data, it has been shown that the application of laser-remelted thermally sprayed Fe-based coatings on AZ91 Mg alloy improves hardness and tribological properties compared to bare Mg alloy and as-sprayed Fe-based coatings.

In situ formation of LDH-based nanocontainers on the surface of AZ91 magnesium alloy and detailed investigation of their crystal structure

In the presented work, the possibility of direct synthesis of LDH (layered double hydroxide) on the AZ91 surface in the presence of a chelating agent (diethylenetriaminepentaacetic acid - DTPA) is reported. Conversion layer of LDH nanocontainers were formed under ambient pressure conditions without carbonate addition in the electrolyte. The obtained LDH was characterized using experimental (SEM, XRD, TGA, XPS, Raman, etc.) and computational methods (thermodynamic calculation, modeling of possible LDH crystal structures). A comparison of three possible LDHs (LDH-OH, -NO3 and -CO3) was performed. Based on the experimental results and crystal simulation approach, it was confirmed, that the mixed LDH-OH/CO3 is grown on the surface in the presence of DTPA pentasodium salt.

Corrosion studies of plasma modified magnesium alloy in simulated body fluid (SBF) solutions

Magnesium (Mg) and its alloys are third-generation biomedical implant material in the biomedical field. The limitation of using Mg in medical applications is its rapid corrosion rate. In the present work, for the first time, AZ91 magnesium alloy surface treated with the inductively coupled Ar/O2 Plasma process to decrease the corrosion rate of the alloy. The oxidation mechanism and surface analysis have been investigated in detail. The electrochemical studies in SBF solution reveal that plasma modified surface increases the corrosion resistance of the alloy compared to the untreated surface.

Development of AZ91/SiC surface composite by FSP: effect of vibration and process parameters on microstructure and mechanical characteristics

A surface composite layer enhances the mechanical characteristics of a surface while retaining the properties of the base material. Friction stir processing (FSP) is a method for forming surface metal matrix composites (SMMCs) that reinforce a surface with particles. In the current study, a new method entitled friction stir vibration processing (FSVP) was applied to form SMMCs on the surface of AZ91 magnesium alloy with SiC particles as the reinforcing particles. Contrary to FSP, in FSVP, the workpiece was vibrated normal to the processing line while the tool rotated and traversed. The microstructure and mechanical properties of friction stir (FS) and friction stir vibration (FSV) processed specimens were evaluated. Additionally, the effects of vibration frequency and process parameters on different characteristics of FS and FSV processed specimens were studied. The results showed that the stir zone grains for FSV processed specimens were finer than those for FS processed specimens, and the second phase particles (SiC particles) had a more homogenous distribution in the former specimens than in the latter specimens. This was related to the effect of workpiece vibration during FSVP, which increased the material deformation and led to enhanced dynamic recrystallization and the breakdown of agglomerated SiC particles. The results indicated that the stir zone grain size decreased, and the distribution homogeneity of the SiC particles increased as vibration frequency increased. It was also observed that the stir zone grain size increased, and the mechanical properties of the processed specimens decreased as tool rotation speed increased.

Microstructural characteristics of chitosan deposited az91 magnesium alloy

Magnesium (Mg) and its alloys have been extensively explored as potential temporary implant materials for orthopaedic applications (e.g. Fracture fixation). Magnesium alloy (AZ91) is used for bone implant application since it has lightest structural element, biocompatible, osteoconductive and its mechanical properties are similar to bone. However, they are prone to corrosion in the human body. Hence in order to reduce the corrosion rate and enhance the biocompatibility and biological properties, AZ91 magnesium alloy surface is modified with chitosan layers. Chitosan coating is proposed to decrease the corrosion rate and improve the bioactivity of AZ91 magnesium alloy. In the study, chitosan was coated on the surface of AZ91 magnesium alloy by spin coating technique. The presence of functional group bands of chitosan coating was confirmed using Fourier transform infrared spectroscopy (FTIR).The surface morphology and the grain size of chitosan on AZ91 magnesium alloy substrate was investigated using Field emission scanning electron microscope (FESEM) analysis. The elemental composition of chitosan was confirmed by Energy dispersive X-ray spectroscopy (EDAX) study. The film thickness was also measured for the coated substrate. Thus chitosan is coated on AZ91 magnesium alloy and characterization are done to confirm the presence of chitosan on AZ91 magnesium substrate which can be further tested for its biocompatible properties and used for orthopaedic applications.

Influence of Aliquat 336 on tribological properties of electroless ternary nanocomposite coatings on AZ91 alloy

Incorporation of fine nanoparticles and cationic surfactant (Aliquat 336) within an ENi–P matrix has given a new dimension to the field of nanocomposite coatings. It describes the surface engineering processes currently used for the protection of AZ91 magnesium alloy surface against wear, including electroless nano-composite coatings. The present work aims to investigate the influence of Aliquat 336 cationic surfactant on the microhardness and tribological properties of electroless (Ni–P–ZnO) ternary alloy nanocomposite coatings on AZ91 magnesium alloy substrate from acidic bath. The results revealed that there was a significant improvement in the microhardness and wear resistance of the coated surface by the addition of cationic surfactant at a concentration of 1.5 g/L as compared to the coating obtained without the addition of cationic surfactant in the chemical bath. These results are thus clearly indicative of the fact that the component of life of members made from substrate subjected to nanocomposite coatings with varying the concentration of surfactant can be greatly improved, thereby preventing early or regular failures, and increasing service life.

Structural Aspects of Remelting of the AZ91 Magnesium Alloy Surface Layer

Abstract In this study, modification of the AZ91 magnesium alloy surface layer with a CO2 continuous wave operation laser has been taken on. The extent and character of structural changes generated in the surface layer of the material was being assessed on the basis of both macro- and microscopy investigations, and the EDX analysis. Considerable changes in the structure of the AZ91 alloy surface layer and the morphology of phases have been found. The remelting processing was accompanied by a strong refinement of the structure and a more uniform distribution of individual phases. The conducted investigations showed that the remelting zone dimensions are a result of the process parameters, and that they can be controlled by an appropriate combination of basic remelting parameters, i.e. the laser power, the distance from the sample surface, and the scanning rate. The investigations and the obtained results revealed the possibility of an effective modification of the AZ91 magnesium alloy surface layer in the process of remelting carried out with a CO2 laser beam.

Corrosion Performance and Preparation of Polyaniline Film on the Surface of AZ91 Magnesium Alloy

Polyaniline (Pani) film was applied onto AZ91 magnesium alloy in aqueous solutions containing oxalic acid and aniline monomer by cyclic voltammetry (CV) technique, which then was characterized by means of IR and SEM technique. Furthermore, the corrosion performance of the coating was evaluated in 3.5%NaCl solution through examining the polarization curves, open circuit potential versus time and the electrochemical impedance spectroscopy (EIS). The results in- dicated that the Pani coating could effectively shift the free corrosion potential much positively for the coated AZ91 magnesium and led to significantly diminish its corrosion current density by two orders of magnitude. Long-term immersion experiments indicated that the Pani coating can effec- tively hinder the permeation of corrosive species toward matrix, thereby prevent AZ91 magnesium alloy from corrosion.

Effects Of Aluminum Sputtering On The Corrosion Resistance Of AZ91 Alloy

Abstract The corrosion resistance of a Magnesium alloy is low and needs to be improved. This research aimed at corrosion-resistance improvement by supatterd deposition aluminium film, which is formed on the surface of AZ91 Magnesium-alloy. Corrosion resistance performed polarization curve measurement, was evaluated in quest of the corrosion rate using the Tafel extrapolation method, and conducted surface observation and EDS analysis by SEM. Although corrosion resistance is not improved only by film forming because of defects in film, corrosion resistance is improved by heat treatment for 3 hours by 553K after sputtering. In the case of heat treated at 623K and 673K for 3 hours, magnesium diffuses through the alminium film and reached the surface of the film. Thus, heat treatment at high temperature degrade the corrosion resistance of the film. The optimization of heat treatment after sputtering is important in this method.

Composition analysis and corrosion performance of a Mo–Ce conversion coating on AZ91 magnesium alloy

A chrome-free chemical conversion coating was deposited on the surface of AZ91 magnesium alloy in a solution containing molybdate and cerium nitrate within a short time. The morphology, composition and structure of the conversion coating were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The corrosion resistance was investigated by polarization curves. The results show that the conversion coating was homogeneous with some small cracks. The coating was mainly composed of MoO3, MoO2, CeO2, Ce2O3, MgO and Mg(OH)2. The corrosion potential for the conversion treated sample shifted positively by approximately 90mV from −1.54V to −1.45V, and the corrosion current density was decreased by approximately two orders of magnitude compared with AZ91 magnesium alloy substrate.

Development of Thermal Barrier Coatings on AZ91 Magnesium Alloy Surface

In this paper, MCrAlY bonding layer was prepared through high velocity-oxygen fuel spray on the AZ91 magnesium alloy surface. 8wt%YSZ ceramic layer was deposited on the surface of bonding layer through atmospheric plasma spraying. The coatings were characterized by XRD and SEM. The hardness of the coating was tested. The coefficients of thermal expansion of the coating were measured through TMA. It was found that there were un-melted 8YSZ particles surrounded by melted particles layer by layer. Parts of ZrO2 transited from cubic to tetragonal. The microhardness of the YSZ coating and bonding layer were 832.1Hv0.3 and 700.3Hv0.3, respectively. The coefficients of thermal expansion of the magnesium alloy, MCrAlY layer and YSZ coating were 42.46 ×10-6·k-1, 15.26 ×10-6·k-1, 9.28 ×10-6·k-1, respectively. The bonding coat matched the magnesium alloy substrate and the YSZ coating well. The dimension of AZ91 magnesium alloy sample was very stabilized before and after coating deposition.

Effective regime of microarc oxidation (MAO) on AZ 91 magnesium alloy

8 1 At the present time, the relative volume of produc� tion and use of magnesium alloys is continuously growing due to their lower density compared to other structural materials (1). Nevertheless the use of parts made of these Mg alloys require anticorrosive coatings on their surfaces. To obtain such protective coatings one of the most promising method consists of Microarc Oxidation (MAO) (2, 3) with a subsequent sealing or varnishing and painting of the surface since microarc coating (MAC) mostly serves as a high� porous layer for further finishing treatment on magne� sium alloys products. It was established (4-6) that the addition of fluo� rinecontaining chemical components in basic elec� trolytes leads to the improvement of the mechanical and tribological properties of microarc oxidation coat� ings formed on the surface of magnesium alloys, increases the efficiency of the MAO process and con� sequently reduces the power consumption of the pro� cess. In this work (3) it is shown that within alkaline phosphate electrolytes, the growth rate of microarc oxidation coating on the surface of AZ91 magnesium alloy is significantly higher (not less than 1.4 times) for a process conducted in the anodic regime than in the anodiccathodic regime. Thus, at the stage of sparking discharges, growth coverage is slowed down with the advent of microarc discharges on a surface of the working electrode. It is obvious that the performance of the process of microarc oxidation of magnesium alloys increases sig� nificantly if it is conducted by passing a direct current between the electrodes in basic electrolytes with the introduction of fluorides. Therefore, the main objec� tive of this work is the investigation of the process to obtain MAO precoats on the surface of magnesium 1 The article was translated by the authors. alloys. This work also aims at establishing technologi� cal parameters that allow us to conduct the process with higher performances. Therefore the optimal con� centration of ammonium fluoride in the base alkaline phosphate electrolyte, the current density and the shape of the current waveform in galvanostatic mode are investigated

Abrasion Resistance of Al-Ni-Mm-Fe Amorphous and Nanocrystalline Composite Coating on the Surface of AZ91 Magnesium Alloy

Abstract An Al-Ni-Mm-Fe amorphous and nanocrystalline composite coating was prepared onto the surface of AZ91 magnesium alloy by high velocity arc spraying process. And the microstructure of the coating was analyzed by scanning electron microscope (TEM) and X-ray diffraction (XRD). The analysis results indicated that the coating consists of amorphous, nanocrystalline and crystalline phases. It has a dense structure with a low porosity of about 2.0%. Its average micro Vickers hardness value is about 330 HV 0.1 , which is five times than that of AZ91 magnesium alloy (62 HV 0.1 ) and four times than that of pure Al coating (71 HV 0.1 ). The abrasion tests showed that the Al-Ni-Mm-Fe coating exhibits a good abrasion resistance.

Preparation of the Multiple Rare Earth Conversion Membrane Based on the Magnesium Alloy AZ91 and their Corrosion Resistance Performance

Chemical membrane coating method was adopted for AZ91 magnesium alloy surface to explore the preparation method for cerium (Ce) conversion membrane, lanthanum (La) conversion membrane and double rare earth conversion membrane. The methods such as Scanning Electron Microscope (SEM), Energy Spectrometer (EDS) and X-ray Crystallography (XRD) were introduced for the detection of conversion membrane. The experiment results revealed that the corrosion resistance of double rare earth conversion membrane would get strengthened firstly, and degraded later along with the prolongation of conversion time. The corrosion resistance from low to high of conversion membrane is cerium (Ce) conversion membrane < lanthanum (La) conversion membrane < double rare earth conversion membrane. Therefore, double rare earth conversion membrane is more effective to improve the corrosion resistance for magnesium alloy and its corrosion resistance is better than that of single rare earth conversion membrane.