Corrosion Properties Of Mg Research Articles

Microstructures and electrochemical corrosion properties of Mg–Al–Pb and Mg–Al–Pb–Ce anode materials

Mg–Al–Pb alloy is a good candidate for the anode material of magnesium seawater battery. For improving the low current utilization efficiency of Mg–Al–Pb alloy, the influence of Ce on the microstructures and electrochemical corrosion properties in a 3.5% NaCl solution was investigated using scanning electron microscope and electrochemical measurements. The results indicate that Ce refines the grain structure of Mg–Al–Pb alloy. The formation of strip Al11Ce3 second phase promotes the uniform distribution of Mg17Al12 phase in Mg–Al–Pb–Ce alloy. The addition of cerium accelerates the discharge activity of Mg–Al–Pb alloy. Due to a large number of cathodic Al11Ce3 and Mg17Al12 phases, Ce promotes the micro-galvanic corrosion and leads to larger corrosion current density and hydrogen evolution rate in Mg–Al–Pb–Ce alloy than those in Mg–Al–Pb alloy. However, Mg–Al–Pb alloy expresses smaller utilization efficiency than Mg–Al–Pb–Ce alloy because of grain detachment.

Galvanic Corrosion Between Weld Zones As Seen in Fusion Welded AZ31B

Research on Mg alloys and their corrosion properties has received increased interest from the automotive, aerospace and naval industries [1]. In particular, the effect that processing, such as welding, has on the intrinsic corrosion properties of Mg and Mg alloys is of interest for the application of architecturally complex Mg structures. In addition, for industrial sandwich panels, Mg has been proposed as a potential material [2]; however, the metallurgy and corrosion of these welded structures must first be understood. The major concern is that the high reactivity of Mg and low electronegative potential makes Mg and its alloys extremely susceptible to galvanic corrosion when alloyed with elements which have dissimilar oxidation potentials. Micro-galvanic coupling may occur due to alloy heterogeneity caused by intermetallic particles (IMPs) [3]. For the alloy of interest in this study, AZ31, alloying elements include Al, Zn, Fe and Mn. Corrosion is exacerbated by differing concentrations of these alloying elements along with phases formed within adjacent regions of the sample during tungsten inert gas (TIG) welding. During processing, a range of solidification-driven microstructures develop across the weld region which are dependent on the initial composition relative to phase equilibrium as well as the competition between the solidification rate and phase transformation characteristics. The nature and the stability of the solid-liquid interface is determined by the thermal and constitutional conditions at this interface [4]. Depending on these conditions, epitaxial interfaces may occur by planar, cellular, or dendritic growth [5]. Both the temperature gradient and growth rate are important for the final microstructure. The weld can be separated into several distinct zones with different microstructures and compositions. These include the Fusion (FZ) and the Heat Affected Zones (HAZ) labeled in Figure 1 where HAZ1 and HAZ2 are specified as two separate regions which have been affected during processing to produce slightly different microstructures from the base plate. The FZ represents a region of direct interaction with the weld tool or heat source such that complete melting and resolidification has occurred. The HAZ represents a region where sufficient heat input via the FZ is being conducted away in the material, resulting in significant recrystallization and grain growth, reduced hardness over the base material and a local variation in chemistry including formation of intermetallic particles. The zones have distinct characteristics which must be identified, dependent on processing regime and starting composition. Processing in this non-equilibrium regime will lead to significant changes in the solidification microstructure within the FZ and HAZs. These changes include localized changes in grain size, precipitate size, shape, distribution and grain orientation. Given the electronegative potential of Mg, these compositional and microstructural variations throughout the weld regions can lead to a pronounced shift in the electrochemical potential across the weld resulting in enhanced galvanic corrosion between adjacent weld zones and within a given weld zone. After welding, the global corrosion rate was determined in 0.6 M NaCl after 3, 24 and 48 hrs of immersion at the open circuit potential (OCP) using electrochemical methods. Time lapse video was recorded from an optical microscope over a 24 hr period to observe the evolution of the corrosion behavior as dark regions [6] across the weld zones with time. The video provided real-time insight regarding the location of corrosion within the weld zone relative to the FZ and the HAZs as a function of time. The controlling region in weld corrosion can be determined from these videos by examining the dominate location of the hydrogen evolution reaction and darkening [6] within the weld cross-section. It is observed that both the HAZ and base plate regions corrode prior to the FZ. The galvanic coupling and evolution of this intrinsic corrosion behavior between the weld zones will be explained using a combination of in-situ time lapse videos, SEM, scanning electrochemical microscopy (SECM), surface analysis and mixed potential theory. Acknowledgements This work was funded by the Office of Naval Research Grant N000141210967 with Dr. David A. Shifler as scientific officer.

Microstructure, mechanical and corrosion properties of Mg–Nd–Zn–Sr–Zr alloy as a biodegradable material

The Mg–2·5Nd–0·3Zn–0·1Sr–0·4Zr (wt-%) alloy was prepared by gravity casting. Solution treatment and extrusion were conducted. The microstructure, mechanical properties, and corrosion behaviour of the alloy under as cast, T4-treated, and as extruded conditions were evaluated using scanning electron microscope, tensile test, microhardometre, immersion test, and electrochemical test. The results show that the as extruded alloy exhibits the highest ultimate tensile strength (231 MPa), elongation (36·6%), and microhardness (57·8 HV). The as cast alloy shows the best corrosion resistance because the relative continuously distributed eutectic phase with noble corrosion potential acts as a corrosion barrier. The as extruded Mg–Nd–Zn–Sr–Zr alloy with high ductility and good corrosion resistance is desirable for preparing biodegradable implants.

The effect of extension twinning on the electrochemical corrosion properties of Mg–Y alloys

The effect of extension twinning formed during compression deformation on the corrosion properties of an Mg–1wt.% Y alloy was investigated using electrochemical tests. The corrosion morphology evolution after immersion in 0.9wt.% NaCl aqueous solutions for various times has been analyzed by scanning electron microscope. The electron back-scatter diffraction result shows the {101¯2} extension twins appear in the deformed Mg–1wt.% Y alloy with a true strain of 1%. The extension twinning accelerates the formation of oxide film and increases charge transfer resistance, resulting in the improvement of corrosion properties. However, it hardly affects the occurrence of microcracks in grain boundaries. The main reasons root in a preferred formation of homogeneous oxide layer in twinning area and low twin boundary energy.

Significant effects of adding trace amounts of Ti on the microstructure and corrosion properties of Mg–6Al–1Zn magnesium alloy

Adding trace amounts of Ti (0.01–0.02wt.%) significantly changed the volume fraction, morphology and size of the β phase in the microstructure of as-cast AZ61 alloy, despite its effect on grain size and texture being small, and strongly affected the corrosion properties of the alloy. The addition of 0.01wt.% Ti drastically increased the corrosion rate in sodium chloride solution due to breaking up of the semi-continuous β phase, which destroyed the barrier effect of the β phase against corrosion attack. The addition of a larger amount of Ti (0.02wt.%) also increased the corrosion rate, but the AZ61 alloy with 0.02wt.% Ti exhibited a much better corrosion resistance than the AZ61 alloy with 0.01wt.% Ti. This was because adding 0.02wt.% Ti greatly decreased the volume fraction and size of the β phase, which reduced the galvanic corrosion effect. The current results suggest that a proper control of trace amounts of Ti has a potential to improve the corrosion properties of cast Mg–Al alloys by modifying the microstructure of the β phase.

Investigations on microstructures, mechanical and corrosion properties of Mg–Gd–Zn alloys

Microstructure, mechanical and corrosion properties of four alloys, Mg–2Gd–2Zn, Mg–2Gd–6Zn, Mg–10Gd–2Zn and Mg–10Gd–6Zn (all are in weight percentages), prepared by gravity permanent mold casting were investigated. The results indicated that the intermetallic phases in the Mg–2Gd–2Zn alloy consisted mainly of (Mg, Zn)3Gd phase whereas the Mg–2Gd–6Zn alloy consisted of both I (Mg3Zn6Gd) and (Mg, Zn)3Gd phases. In addition, few Mg–Gd and Mg–Zn binary phases were also present in both the alloys. Lamellar long period stacking ordered (LPSO) phase was observed in alloys containing high concentrations of Gd (Mg–10Gd–2Zn and Mg–10Gd–6Zn alloys) in addition to the continuously distributed (Mg,Zn)3Gd phase along the interdendritic regions and grain boundaries. A small fraction of X phase (Mg12ZnGd) was also present in Mg–10Gd–2Zn alloy. Mg–10Gd–xZn alloys (x=2,6) exhibited higher yield strength due to the higher solute contents and the presence of LPSO phase in the matrix, but showed poor elongation due to the coarse continuous second phase at the boundary. Low Gd-containing alloys showed better elongation to failure and moderate strength due to the lower volume fraction of fine scale second phases. Corrosion resistances of the alloys decreased with increase in the total amount of alloying elements. Increase in Zn content from 2% to 6% in Mg–2Gd–xZn alloys did not alter the corrosion properties much; however, this increase in the high Gd-containing alloys had significant detrimental effects on the corrosion properties due to the significant increase in the volume of the second phases. In all the alloys, galvanic corrosion due to the second phase and filiform corrosion dominated the earlier stages of corrosion, and after long immersion times, the second phase, (Mg,Zn)3Gd, was found to become unstable and dissolved, leading to intergranular corrosion.

Mechanical and corrosion properties of Mg based alloys considered for medical applications as biodegradable materials

Magnesium and its alloys are considered as suitable biodegradable materials which can be gradually dissolved in organism without production of toxic compounds. The present study is oriented on new group of possible biodegradable materials based on Mg-LMM (Mg- low melting metals) alloys. Due to the limited information about the effect of Ga, Sn and In on mechanical and corrosion properties, structure studies, mechanical and corrosion testing were performed. Corrosion behaviour of materials was studied using measuring of weight changes, Mg ions release and also by EIS technique in SBF (simulated body fluid) that is close in composition with human plasma. The obtained results indicate positive effect of both Ga and Sn on tensile and compressive properties, compared to the almost neglectable effect of In. On the contrary, all materials were characterized by decreased corrosion resistances compared to pure Mg. Mainly structure conditions were responsible for observed differences in corrosion rates.

Effects of super-high pressure on microstructures, nano-mechanical behaviors and corrosion properties of Mg–Al alloys

Abstract The aim of this study was to investigate the effects of super-high pressure solidification (2 and 4 GPa) on microstructures, nano-mechanical behaviors and corrosion properties of Mg-30 wt.% Al alloy. The lattice parameter (a) of Mg matrix is decreased and the c/a value is increased owing to the increased Al concentration in Mg matrix. In contrast to the as-cast sample or other super-high pressure samples, the Mg matrix is more homogeneous and the net-like eutectic phase becomes finer after super-high pressure solidification at 800 °C under 2 GPa. In addition, the area fraction of eutectic phase is reduced with increasing the exterior pressure and temperature during the solidification, whilst the Al concentration in both the Mg matrix and the eutectic phase are enhanced. The nanoindentation results indicate that both the hardness and Young’s modulus are sensitive to the solidification pressure and temperature. The Tafel curves and electrochemical impedance spectroscopes results reveal the corrosion properties of the sample at 800 °C under 2 GPa are remarkably improved due to the formation of a compact and continuous oxide layer.

Age hardening behaviors, mechanical and corrosion properties of deformed Mg–Mn–Sn sheets by pre-rolled treatment

The age behaviors, mechanical and corrosion properties of Mg–1.5Mn–xSn (x=1 and 5wt.%) alloys under three aging conditions have been investigated. The results reveal that both age behaviors and mechanical properties are improved with the increment of Sn. Meanwhile, the mechanical properties of EA (extrusion+artificial aging) state Mg–1.5Mn–5Sn alloy are higher than those of SA (solid solution+artificial aging) state sample, which are mostly attributed to fine grain and high density secondary precipitate. In addition, an accompanying improvement in age hardening response and strength is achieved in ERA (extruded+rolled+aging) state alloy compared with EA state one. The main reasons are related to the formations of a large number of dislocations and deformation twins, which provide effective nucleation sites to form fine β-Mg2Sn strengthening precipitates during the following aging process. In addition, compared with EA state sample, a lower corrosion rate of ERA alloy is confirmed by Tafel curves and electrochemical impedance spectroscopy results, which is mainly related to the formation of a thick anodic passivation film on the surface.

Effects of cooling rate on microstructure, mechanical and corrosion properties of Mg–Zn–Ca alloy

Mg69Zn27Ca4 alloys with diameters of 1.5, 2 and 3 mm were fabricated using copper mold injection casting method. Microstructural analysis reveals that the alloy with a diameter of 1.5 mm is almost completely composed of amorphous phase. However, with the cooling rate decline, a little α-Mg and MgZn dendrites can be found in the amorphous matrix. Based on the microstructural and tensile results, the ductile dendrites are conceived to be highly responsible for the enhanced compressive strain from 1.3% to 3.1% by increasing the sample diameter from 1.5 mm to 3 mm. In addition, the Mg69Zn27Ca4 alloy with 1.5 mm diameter has the best corrosion properties. The current Mg-based alloys show much better corrosion resistance than the traditionally commercial wrought magnesium alloy ZK60 in simulated sea-water.

Microstructure, mechanical and corrosion properties of Mg–Dy–Gd–Zr alloys for medical applications

In previous investigations, a Mg–10Dy (wt.%) alloy with a good combination of corrosion resistance and cytocompatibility showed great potential for use as a biodegradable implant material. However, the mechanical properties of Mg–10Dy alloy are not satisfactory. In order to allow the tailoring of mechanical properties required for various medical applications, four Mg–10(Dy+Gd)–0.2Zr (wt.%) alloys were investigated with respect to microstructure, mechanical and corrosion properties. With the increase in Gd content, the number of second-phase particles increased in the as-cast alloys, and the age-hardening response increased at 200°C. The yield strength increased, while the ductility reduced, especially for peak-aged alloys with the addition of Gd. Additionally, with increasing Gd content, the corrosion rate increased in the as-cast condition owing to the galvanic effect, but all the alloys had a similar corrosion rate (∼0.5mmyear−1) in solution-treated and aged condition.

Effect of manganese additions on the corrosion behavior of an extruded Mg–5Al based alloy

The effect of manganese on the corrosion properties of Mg–5Al alloy was investigated by electrochemical techniques in 0.6M NaCl solution and surface analyses. The electrochemical tests indicated that the corrosion rate and hydrogen evolution of the Mg–5Al specimens decreased with increasing Mn content. Surface analyses indicated that Mn promoted the formation of the corrosion products in the absence of Mn products. In addition, to this Mn addition also resulted in reduction of grain size and increase of Mn in the Mg matrix.

In vitro and in vivo studies on a Mg–Sr binary alloy system developed as a new kind of biodegradable metal

Magnesium alloys have shown potential as biodegradable metallic materials for orthopedic applications due to their degradability, resemblance to cortical bone and biocompatible degradation/corrosion products. However, the fast corrosion rate and the potential toxicity of their alloying element limit the clinical application of Mg alloys. From the viewpoint of both metallurgy and biocompatibility, strontium (Sr) was selected to prepare hot rolled Mg–Sr binary alloys (with a Sr content ranging from 1 to 4wt.%) in the present study. The optimal Sr content was screened with respect to the mechanical and corrosion properties of Mg–Sr binary alloys and the feasibility of the use of Mg–Sr alloys as orthopedic biodegradable metals was investigated by in vitro cell experiments and intramedullary implantation tests. The mechanical properties and corrosion rates of Mg–Sr alloys were dose dependent with respect to the added Sr content. The as-rolled Mg–2Sr alloy exhibited the highest strength and slowest corrosion rate, suggesting that the optimal Sr content was 2wt.%. The as-rolled Mg–2Sr alloy showed Grade I cytotoxicity and induced higher alkaline phosphatase activity than the other alloys. During the 4weeks implantation period we saw gradual degradation of the as-rolled Mg–2Sr alloy within a bone tunnel. Micro-computer tomography and histological analysis showed an enhanced mineral density and thicker cortical bone around the experimental implants. Higher levels of Sr were observed in newly formed peri-implant bone compared with the control. In summary, this study shows that the optimal content of added Sr is 2wt.% for binary Mg–Sr alloys in the rolled state and that the as-rolled Mg–2Sr alloy in vivo produces an acceptable host response.

Effect of Ce additions on high temperature properties of Mg–5Sn–3Al–1Zn alloy

The electrochemical behaviour of Mg–xCe–1Zn (x = 3, 8 and 13 wt-%) alloys has been investigated. The alloys were fabricated using a vacuum induction melting method under an argon atmosphere. Potentiodynamic polarisation was carried out in 3·5%NaCl solution of pH 7·2 at room temperature to evaluate the corrosion properties of Mg–xCe–1Zn (x = 3, 8 and 13 wt-%) alloys. The microstructure of the Mg–(3, 8 and 13 wt-%)Ce–1Zn alloys mainly consisted of α-Mg and eutectic Mg12Ce phase. With the increase in Ce contents, the volume per cent and size of the eutectic Mg12Ce phase were increased. Results indicated that the corrosion rate of Mg–xCe–Zn alloy was increased by excessive Ce addition.

Electrochemical behaviour of Mg–Ce–Zn system

In the present work, the electrochemical behaviour of Mg–xCe–1Zn (x = 3, 8 and 13 wt-%) alloys has been investigated. The alloys were fabricated using an induction melting method under an argon atmosphere. Potentiodynamic polarisation was carried out in 3·5%NaCl solution of pH 7·2 at room temperature to evaluate the corrosion properties of Mg–xCe–1Zn (x = 3, 8 and 13 wt-%) alloys. The microstructure of the Mg–(3, 8 and 13 wt-%)Ce–1Zn alloys mainly consisted of α-Mg and eutectic Mg12Ce phase. With the increase in Ce contents, the volume per cent and size of the eutectic Mg12Ce phase were increased. Results indicated that the corrosion rate of Mg–xCe–Zn alloy was increased by excessive Ce addition.

Microstructure effects on the electrochemical corrosion properties of Mg – 4.1% Ga – 2.2% Hg alloy as the anode for seawater-activated batteries

Mg–Ga–Hg alloy is a new material with special electrochemical corrosion properties that make it ideal for use in seawater-activated battery anodes. The effects of microstructure and phase transformation on the electrochemical properties of the Mg – 4.1% Ga – 2.2% Hg alloy were studied and compared with Mg–Al system alloys. The results show that the Mg – 4.1% Ga – 2.2% Hg alloy, when used as an anode, has an appropriate corrosion potential in a half-cell test and superior electrochemical properties in a single cell assembled with CuCl. The Mg 3Hg and Mg 21Hg 5Ga 3 phases of the alloy influence its corrosion behaviour and provide a steady corrosion potential during the discharge process.

Effect of Ca and Sr additions on high temperature and corrosion properties of Mg–4Al–2Sn based alloys

This study examined the effects of Ca and Sr addition on the creep and corrosion properties of Mg–Al–Sn based alloys with the aim of developing new Mg–Al–Sn–x alloys for automotive powertrain applications. The materials were cast using the squeeze casting process to obtain a dense microstructure without pores. Creep tests were carried out at a constant temperature between 150°C and 200°C and a constant applied stress between 50 and 80MPa until the minimum creep rate had been reached. Potentiodynamic and immersion tests were carried out to evaluate corrosion properties of the alloys. The creep and corrosion resistance were improved by adding Ca and Sr.

Effects of flux containing YCl 3 on the yttrium loss, mechanical and corrosion properties of Mg–10Gd–3Y–0.5Zr alloy

New fluxes containing YCl 3 were developed to refine Mg–10Gd–3Y–0.5Zr (GW103K) alloy, with the aim to suppress the loss of expensive heavy rare earth element Y, but also to improve the removal of nonmetallic inclusions. The Y loss, microstructure, mechanical and corrosion properties were investigated. It was found that the loss of Y in the alloy decreased with the increasing of YCl 3 in the flux. Thermodynamic calculation indicated that the main reason could be attribute to the decline of the Gibbs free energy, which slows down the reaction rate between MgCl 2 and Y. The study demonstrated that the fluxes containing 5 wt.% YCl 3 additions also exhibited excellent capability of removing nonmetallic inclusions. This greatly improved the mechanical and corrosion properties of GW103K alloy.

Effect of mischmetal on the corrosion properties of Mg–5Al alloy

The effect of mischmetal (Mm) on the corrosion properties of Mg–5Al alloy was investigated by electrochemical techniques in 0.01 M NaCl solution as the alkaline condition (pH 12) and surface analyses. The electrochemical tests indicated that the pitting potential, time to pitting initiation, and charge transfer resistance of the Mg–5Al specimens increased with increasing Mm content. Surface analyses indicated that Mm promoted the formation of passive film in the absence of Mm products. In addition, the benefits of Mm addition are the refinement of the precipitates and reduction in grain size.

Gd contents, mechanical and corrosion properties of Mg–10Gd–3Y–0.5Zr alloy purified by fluxes containing GdCl 3 additions

The effects of GdCl 3 in flux on the loss of Gd, microstructure, mechanical and corrosion properties of Mg–10 wt.% Gd–3 wt.% Y–0.5 wt.% Zr (GW103K) alloy were investigated. The results indicate that the loss of Gd in the alloy decreased when the melts were refined by fluxes containing GdCl 3 additions. Thermodynamic analysis revealed that the decline of Gibbs free energy is the main reason, which slows down the reaction rate between MgCl 2 and Gd in melts. In as-cast condition, after treated with 5 wt.% GdCl 3 additions, tensile yield strength, ultimate tensile strength and elongation of the alloy could reach the peak value of 201.51 MPa, 154.68 MPa and 2.56% respectively. 5 wt.% NaCl aqueous solution immersion test shows that the corrosion rate of GW103K alloy decreased to 0.437 mg cm −2 d −1 after refined by JDMJ + 5 wt.% GdCl 3. However GdCl 3 additions have no effects on microstructure and fracture pattern of GW103K alloy.