Effect of heat treatment on anodization and electrochemical behavior of AZ91D magnesium alloy

2005 ◽  
Vol 20 (10) ◽  
pp. 2763-2771 ◽  
Author(s):  
Houng-Yu Hsiao ◽  
Wen-Ta Tsai
Keyword(s):  
Heat Treatment ◽  
Magnesium Alloy ◽  
Polarization Resistance ◽  
Solution Heat Treatment ◽  
Electrochemical Impedance ◽  
Cast Alloy ◽  
Anodic Film ◽  
Air Cooling ◽  
Anodic Films ◽  
Az91d Magnesium Alloy

The anodic films formed on AZ91D magnesium alloy after heat treatment were analyzed and their electrochemical properties were investigated. The results showed that the cooling rate had a significant influence on the microstructure evolution of the AZ91D magnesium alloy after solution heat treatment at 440 °C for 20 h in N2 atmosphere. A single-phase microstructure was observed when the alloy was quenched in water after solution heat treatment. However, a duplex structure consisting of both α and β phases was found if the solution-annealed alloy was cooled in air. The differences in microstructure of the heat treated AZ91D magnesium alloy gave rise to a significant change in the property of the anodic film formed in 3 M KOH + 0.21 M Na3PO4 + 0.6 M KF + 0.15 M Al(NO3)3 electrolyte. During the early stage of anodization, for the as-cast alloy, inhomogeneous anodic films were formed exhibiting relative rough surface appearances. A rather smooth anodic film was formed for the solution-annealed AZ91D magnesium alloy either followed by air cooling or water-quenched. The surface and cross section appearance was almost the same regardless of the prior heat treatment after anodizing for 20 min. The corrosion resistances of the various anodized AZ91D magnesium alloy were evaluated and compared by employing electrochemical impedance spectroscopy (EIS). The results demonstrate that the anodic film formed on the water-quenched AZ91D magnesium alloy had a slightly higher polarization resistance than that formed on the as-cast alloy. The highest polarization resistance of anodic film was found for that formed on annealed and air-cooled alloy. The presence of Al-rich β phase on the surface gave rise to the formation of a more protective anodic film which consisted of a great amount of Al2O3.

TEM Investigations of Electron 21 Magnesium Alloy

2007 ◽  
Vol 130 ◽  
pp. 175-180 ◽  
Author(s):  
Andrzej Kiełbus
Keyword(s):  
Heat Treatment ◽  
Magnesium Alloy ◽  
Solution Heat Treatment ◽  
Cast Alloy ◽  
Solution Treatment ◽  
Air Cooling ◽  
Transmission Electron ◽  
The Matrix ◽  
Cast Condition ◽  
Cast Microstructure

The paper presents results of TEM investigations of Elektron 21 magnesium alloy in as cast condition and after heat treatment. The compositions of the Elektron 21 alloy used in the present study was Mg-2,7%wtNd-1,2%wtGd-0,47%wtZr. Solution heat treatment was performed at 520°C/8 h/water. Ageing treatments were performed at 200°C/4÷96h and 300°C/48h with cooling in air. The as-cast microstructure and microstructural evolution during heat treatment were examined by transmission electron microscopy. Samples were prepared using Gatan PIPS ion mill. Examinations were performed in a JEM 2010 ARP microscope. The microstructure of the cast alloy consists of a-Mg phase matrix with precipitates of Mg12(Ndx,Gd1-x) phase at grain boundaries. After solution treatment the Mg12(Ndx,Gd1-x) phase dissolved in the matrix. The ageing treatment applied after solution treatment with air-cooling caused precipitation of a β’ and β phases.

Improvement of Corrosion Resistance of Rare Earth Element (REE)-Based Anodic Oxidation Coating on AZ91D Magnesium Alloy

2012 ◽  
Vol 187 ◽  
pp. 210-214 ◽  
Author(s):  
M.Z.M. Zain ◽  
S. Illias ◽  
M. Mat Salleh ◽  
K. Azwan Ismail ◽  
Z. Nooraizedfiza
Keyword(s):  
Corrosion Resistance ◽  
Rare Earth ◽  
Magnesium Alloy ◽  
Anodic Oxidation ◽  
Earth Metal ◽  
Immersion Test ◽  
Corrosion Property ◽  
Anodic Film ◽  
Anodic Films ◽  
Az91d Magnesium Alloy

Anodization is a useful technique for forming protective films on magnesium alloys and improves its corrosion resistance. Based on the rare earth metal (REE) salt solution, the optimum parameter was selected by comparing the anti-corrosion property of anodic film. The structure, component and surface morphology of anodic film and cross-section were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS). The corrosion behavior was evaluated by immersion test. In this paper, a dense anodic film approximately 20 µm thick was prepared on a AZ91D magnesium alloy through anodic oxidation coating. The results show that the anodic films were mainly composed of Mg17Al12, Mg17La2, MgO and amorphous compounds. The best corrosion resistance was obtained with specimen anodized in solution containing both lanthanum nitrate and magnesium, whose corrosion resistance is approximately 3 times higher than that of as-received AZ91D magnesium alloy.

Effects of Sb Addition on Heat-Treated Microstructure and Mechanical Properties of AZ61-0.7Si Magnesium Alloy

2012 ◽  
Vol 190-191 ◽  
pp. 1306-1310 ◽  
Author(s):  
Ming Bo Yang ◽  
Hong Liang Li ◽  
Ren Ju Cheng ◽  
Hong Jun Hu
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Magnesium Alloy ◽  
Solution Heat Treatment ◽  
Cast Alloy ◽  
Chinese Script ◽  
Creep Properties ◽  
Mg2si Phase ◽  
Microstructure And Mechanical Properties ◽  
Heat Treated

In this paper, the effects of Sb addition on heat-treated microstructure and mechanical properties of AZ61-0.7Si magnesium alloy were investigated. The results indicate that the solution heat treatment can modify the Chinese script shaped Mg2Si phase in the AZ61-0.7Si alloy. After solutionized at 420°C, the morphology of the Mg2Si phase in the AZ61-0.7Si alloy changes from the Chinese script shape to the short pole and block shapes, and the higher modification efficiency could be obtained for the alloy with the addition of 0.4 wt.%Sb. In addition, the effect of the solution heat treatment on the morphology of the Mg2Si phase can also result in the improvement of tensile and creep properties for the AZ61-0.7Si alloy. After solutionized at 420°C for 24h and followed by aging treatment at 200°C for 12h, the AZ61-0.7Si alloy exhibits higher tensile and creep properties than that of the as-cast alloy, and the properties improvement resulted from heat treatment, is more obvious for the AZ61-0.7Si alloy with the addition of 0.4 wt.%Sb.

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

2018 ◽  
Vol 1148 ◽  
pp. 122-127 ◽  
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.

Precipitate and Age Hardening Response of As-Cast Mg-8Yb-0.5Zr Magnesium Alloy

2011 ◽  
Vol 399-401 ◽  
pp. 17-20
Author(s):  
Wen Bin Yu ◽  
Zhi Qian Chen ◽  
Mang Zhang ◽  
Zhou Yu
Keyword(s):  
Heat Treatment ◽  
Magnesium Alloy ◽  
Grain Boundaries ◽  
Microstructure Evolution ◽  
Solution Heat Treatment ◽  
Artificial Aging ◽  
Precipitation Hardening ◽  
Intermetallic Phase ◽  
Age Hardening ◽  
Maximum Hardness

The precipitation hardening response of as-cast Mg-8Yb-0.5Zr magnesium alloy was investigated in the present work. The microstructure evolution of the alloy illustrated that Mg2Yb intermetallic phase was dissolved by solution heat treatment at 520°C for 12 hours. An apparent precipitation hardening response in Mg-8Yb-0.5Zr was discovered after artificial aging at 150°C, with maximum hardness increment of about 80 percent at the peak condition. It was found that the precipitates of the alloy were in the shape of two conjoined cosh and globe about 50 nm, and precipitated preferentially on grain boundaries and dislocations.

Effects of Post Heat Treatment on the Interfacial Characteristics of Aluminum Coated AZ91D Magnesium Alloy

2007 ◽  
Vol 546-549 ◽  
pp. 529-532 ◽  
Author(s):  
Jin Zhang ◽  
Ying Wang ◽  
Rong Chang Zeng ◽  
Wei Jiu Huang
Keyword(s):  
Heat Treatment ◽  
Magnesium Alloy ◽  
Spray Coating ◽  
Aluminum Coating ◽  
Diffusion Kinetics ◽  
Post Heat Treatment ◽  
Az91d Magnesium Alloy ◽  
Metallurgical Bonding ◽  
Kinetics Of ◽  
Interfacial Characteristics

Aluminum spray coating was applied onto AZ91D magnesium alloy. The effects of post heat treatment on the interfacial characteristics, especially the diffusion kinetics of magnesium and aluminum atoms across the interface were studied in this paper. It was observed that there was an obvious interface between the aluminum coating and the magnesium alloy substrate. It was found that post heat treatment could reduce the number of pores existed in the aluminum coating. The post heat treatment resulted in not only the change in the composition and microstructure of the aluminum coating, but also the improved metallurgical bonding between the coating and the substrate.

Tribological and ageing behavior of Az91D magnesium alloy fortified with nano lanthanum and nanoceria by stir casting for aviation application

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Mohammed Fahad ◽  
Bavanish B.
Keyword(s):  
Heat Treatment ◽  
Wear Resistance ◽  
Magnesium Alloy ◽  
Cerium Oxide ◽  
Stir Casting ◽  
Cerium Oxide Nanoparticles ◽  
Oxide Nanoparticles ◽  
Az91d Alloy ◽  
Content Type ◽  
Az91d Magnesium Alloy

Purpose The aviation field requires a material with the ability to withstand severe environmental conditions. The purpose of this paper is to provide higher wear resistance and improve the lifetime of aircraft. Hence, it is vital to enhance the wear resistance and strength of the material. Design/methodology/approach In this investigation, the Az91D magnesium alloy was reinforced with lanthanum (La2O3) and cerium oxide (CeO2) nanoparticles by stir casting and heat treatment process and the tribological and mechanical properties were analyzed. Findings The results showed the Az91D/CeO2 composite exhibited higher density (1.96 g/cm3) and lower porosity (1.01%) compared to other materials due to the diffusion of CeO2 nanoparticles in between the atoms of Az91D alloy. The hardness of Az91D/ CeO2 & Az91D/ La2O3 was improved by 38% and 34%, respectively, compared to Az91D alloy owing to the reinforcing effect of hard nanoparticles. Further, the inclusion of nanoparticles decreased the mass loss and showed lower wear rate compared to the Az91D alloy due to the pinning effect of nanoparticles. In addition, the friction coefficient was observed in the order of Az91D > Az91D/ La2O3 > Az91D/ CeO2. Moreover, the heat treatment displayed positive results on the properties of all the materials. Originality/value This work is original as the combination of cerium oxide nanoparticles with Az91D magnesium alloy is not tried by earlier investigators. Further, the comparative performance of both lanthanum and cerium oxide nanoparticles on the tribological and mechanical behavior of Az91D alloy has been analyzed for aviation application. This study will provide new information to the scientific world to increase the lifetime of aviation structures.

A Novel Electroless Ni-P Deposition on AZ91D Magnesium Alloy

2010 ◽  
Vol 154-155 ◽  
pp. 1330-1335
Author(s):  
Li Ping Wu ◽  
Zhong Dong Yang ◽  
Jing Jing Zhao ◽  
Yong Ping Xie
Keyword(s):  
Magnesium Alloy ◽  
Electrochemical Impedance ◽  
Electroless Nickel ◽  
Deposition Process ◽  
Chemical Compositions ◽  
Good Adhesion ◽  
Plating Bath ◽  
Az91d Magnesium Alloy ◽  
Structure Morphology ◽  
Electroless Ni

Currently, most of electroless nickel phosphorus plating on magnesium alloys has following disadvantages. First, it has been suffering from corrosion issues caused by acidic electroless bath. Second, in order to increase the strength of Ni-P coatings to the Mg substrate, the pretreatments for electroless Ni-P employ hydrofluoric acid (HF) and hexavalent chromium (Cr6+) which can cause pollution and health problems . In this paper, we developed HF-free and alkaline electroless Ni-P deposition process on AZ91D magnesium alloy which avoids the use of SO42- and Cl- ions in the electroless plating bath, thus leading to good adhesion and corrosion resistance of electroless Ni-P coating on magnesium alloy. XRD, SEM, EDS techniques were used to study the structure, morphology, and chemical compositions of the conversion coating and Ni-P coating, respectively. Polarization measurements indicated that the corrosion rate of Ni-P coated Mg was six times lower than that of bare Mg. Electrochemical impedance spectroscopy (EIS) also showed that the Ni-P coating could effectively protect Mg alloy from corrosion.

DSC and Microstructural Investigations of the Elektron 21 Magnesium Alloy

2010 ◽  
Vol 638-642 ◽  
pp. 1447-1452 ◽  
Author(s):  
Andrzej Kiełbus ◽  
Tomasz Rzychoń ◽  
Roman Przeliorz
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
Magnesium Alloy ◽  
Solution Heat Treatment ◽  
Casting Alloy ◽  
Solution Hardening ◽  
Ageing Treatment ◽  
Aerospace Application ◽  
Different Temperatures ◽  
Cast Condition

The paper presents the results of DSC and microstructural investigations of Elektron 21 magnesium alloy in as cast condition and after solution hardening. Elektron 21 is a magnesium based casting alloy containing neodymium and gadolinium for used to at 200°C in aerospace application. The solution heat treatment was performed at 520°C/8h/water. Ageing treatment was performed at different temperatures 200, 250, 300 and 350°C, then quenched in air. The microstructure of Elektron 21 in as cast condition consists of primary solid solution α -Mg grains with eutectic α-Mg + Mg3(Nd,Gd) phase and regular precipitates of MgGd3 phase. After DSC investigations three exothermal signals has been observed. First exothermal signal at ~170÷245°C assigned to an undifferentiated formation of the metastable phases β” and β’ and the second one at ~280°C corresponded to the formation of a stable β (Mg3Nd) phase. The last signal at ~300°C was connected to the formation of Mg41Nd5 phase. Regular precipitates of MgGd3 phase have been also observed. TEM investigation confirmed that the Elektron 21 alloy precipitate from the solid solution according to the sequence of the following phases: α–Mgβ”β’β(Mg3Nd)Mg41Nd5

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