Mg-Mn Alloy Research Articles

Effect of Mn additions on diffusion behavior of Fe in molten magnesium alloys by solid-liquid diffusion couples

Abstract The effect of Mn additions on diffusion behavior of iron in molten magnesium alloys was investigated by solid-liquid diffusion couples at 720-800 °C. The Fe concentration curves in molten Mg and Mg-2Mn alloys were measured. The diffusion coefficients of Fe in molten magnesium alloys were decreased with Mn added at the same temperature. The reason was that no transition layer was formed at the interfaces of Fe/Mg diffusion couples, but continuous transition layers were formed at the interfaces of Fe/(Mg-2Mn) diffusion couples. The activation energies of Fe diffuse in Mg-(0 and 2)Mn melts were determined from the diffusion coefficients in the temperature range of 720–800 °C to be 8.83 ± 0.23 kJ/mol and 11.88 ± 0.14 kJ/mol, respectively. This study demonstrates that the transition layer at the interface of Fe/(Mg-2Mn) diffusion couple is an effective barrier to Fe atoms diffuse into the Mg-2Mn melt. The mechanism of iron removal in Mg-Mn alloy melt was revealed.

Effect of Alloying Elements on Nano-ordered Wear Property of Magnesium Alloys

The effect of alloying elements on nano-ordered wear properties was investigated using fine-grained pure magnesium and several types of 0.3 at. pct X (X = Ag, Al, Ca, Li, Mn, Y, and Zn) binary alloys. They had an average grain size of 3 to 5 μm and a basal texture due to their production by the extrusion process. The specific wear rate was influenced by the alloying element; the Mg-Ca and Mg-Mn alloys showed the best and worst wear property, respectively, among the present alloying elements, which was the same trend as that for indentation hardness. Deformed microstructural observations revealed no formation of deformation twins, because of the high activation of grain boundary-induced plasticity. On the contrary, according to scratched surface observations, when grain boundary sliding partially contributed to deformation, these alloys had large specific wear rates. These results revealed that the wear property of magnesium alloys was closely related to the plastic deformation mechanism. The prevention of grain boundary sliding is important to improve the wear property, which is the same as that of a large-scale wearing configuration. One of the influential factors is the change in the lattice parameter with the chemical composition, i.e., ∂(c/a)/∂C. An alloying element that has a large value of ∂(c/a)/∂C effectively enhances the wear property.

Explanation for anomalous environmentally assisted cracking behaviour of a wrought Mg–Mn alloy in chloride medium

The role of arsenate ions and cathodic charging on the environmentally assisted cracking (EAC) behaviour of a Mg-Mn alloy in 0.6M NaCl saturated with Mg(OH)2 was investigated. The stability of the surface film and the repassivation kinetics have been found to play a critical role in the EAC tendency of the alloy than hydrogen-assisted mechanisms. Cathodic charging was found to be beneficial in lowering the EAC tendency of the alloy.

Enhancement of room temperature stretch formability via grain boundary sliding in magnesium alloy

The enhancement method of room temperature formability was investigated by controlling the rate-controlling mechanism. Wrought processed pure magnesium and its alloys (Mg-Al-Zn and Mg-Mn alloys), which have a basal texture, were used in this study. Pure magnesium had two kinds of average grain sizes (~7µm and ~30µm), and the other alloys were 20–30µm in average grain size. The forming load vs. displacement curves in Erichsen tests were not influenced by the forming rate in the Mg-Al-Zn alloy; however, the fine-grained pure magnesium and Mg-Mn alloy showed a high forming rate dependence. The limited dome heights were 4.7, 2.0 and 5.2 for the fine-grained pure magnesium, Mg-Al-Zn and Mg-Mn alloys, respectively. Deformed microstructural observations revealed that, in the meso-grained pure magnesium and the Mg-Al-Zn alloy, deformation twins formed and were closely related to crack propagation. On the other hand, the formation of such deformed structures was difficult to identify in the fine-grained pure magnesium and meso-grained Mg-Mn alloy. The good stretch formability and high rate dependence of the fine-grained pure magnesium and Mg-Mn alloy resulted from the major contribution of grain boundary sliding to deformation during Erichsen testing. The addition of an alloying element, which plays a role in the enhancement for grain boundary sliding, is quite effective to improve the room temperature stretch formability.

The Enhancement of Mg Corrosion Resistance by Alloying Mn and Laser-Melting.

Mg has been considered a promising biomaterial for bone implants. However, the poor corrosion resistance has become its main undesirable property. In this study, both alloying Mn and laser-melting were applied to enhance the Mg corrosion resistance. The corrosion resistance, mechanical properties, and microstructure of rapid laser-melted Mg-xMn (x = 0–3 wt %) alloys were investigated. The alloys were composed of dendrite grains, and the grains size decreased with increasing Mn. Moreover, Mn could dissolve and induce the crystal lattice distortion of the Mg matrix during the solidification process. Mn ranging from 0–2 wt % dissolved completely due to rapid laser solidification. As Mn contents further increased up to 3 wt %, a small amount of Mn was left undissolved. The compressive strength of Mg-Mn alloys increased first (up to 2 wt %) and then decreased with increasing Mn, while the hardness increased continuously. The refinement of grains and the increase in corrosion potential both made contributions to the enhancement of Mg corrosion resistance.

Characterization of Binary Mg-Mn Alloy Synthesized through Mechanical Alloying: Effects of Milling Speed

In this work, the effect of the milling speed on the properties of biodegradable Mg-1Mn alloy prepared by mechanical alloying was investigated. The magnesium-based alloy was prepared in solid state route using a high energy planetary mill. A mixture of pure magnesium and manganese powder was mechanically alloyed for 5 hours in argon atmosphere. Milling process was performed at various rotational speeds in order to investigate milling speed effect (i.e., 100, 200, 300 and 400 rpm) on phase formation and bulk properties. The as-milled powder was uniaxially compacted by cold pressing under 400 MPa at room temperature and sintered in argon atmosphere at 500 °C for an hour. X-ray diffraction analysis indicated that a single α-Mg phase was formed in magnesium matrix after sintering process. An increase in milling speed up to 300 rpm resulted in an increase in density and hardness of the binary alloy. The changes of bulk properties of the Mg-Mn alloys were correlated to the formation of solid solution phase and a reduction of porosity which led to an increasing in densification.

Impact Performance of ZnAl27Cu2.5MgMn Alloy from Room Temperature to 250°C

The impact performance of ZnAl27Cu2.5MgMn alloy from room Temperature to 2500 °C has been investigated by pendulum impact testing. The surface morphology of impact fracture is observed by scan electron microscope (SEM). The results indicate that impact energy of the alloy decreases as the temperature increases when the temperatures are lower than 100°C. Between 100°C and 200°C, impact energy increases as the temperature increases. And when the temperature exceeds 250°C, impact energy decreases dramatically. Impact energy gets to the maximum at room temperature. Impact behavior of the alloy can be evaluated by the width of impact spectrum curve. The wider the peak of impact spectrum curve, the higher the impact toughness. Whereas impact toughness is worse if peak is narrow.

Electrochemical Corrosion Behaviour of Mg-(Ca,Mn) Sacrificial Anodes

The aim of the study is to identify the effect of Ca in Mg-Mn alloy on electrochemical corrosion behavior for the development of high performance sacrificial anode. Mg alloys were fabricated by casting technique under an inert atmosphere. 0.35 ~ 1.11 wt.% of Ca were added as alloying element. The finding shows that the addition of small Ca in Mg-Mn anodes was found not significantly affecting the corrosion rate. However, small content of Ca was as much as necessary improving electronegativity of open circuit potential and modifying anodic polarization in promoting the instabilities of surface passive layer hence results in the further dissolution process between ion and alloy species underneath. No passivation occurs on the standard samples. Pitting profile only occur on Mg-Mn anode that has lower Ca content (0.35 wt. %). An XRD result shows no present of Mg2Ca phase on the as-cast anode containing 1.11 wt. % Ca. As a conclusion, the influence of small content of Ca was profoundly modifying electrochemically behaviour of Mg containing Mn anodes except corrosion rate.

Acoustic Emission Study of Mg-Mn Extruded Alloys with Prospective Mechanical Properties

This paper focuses on the analysis of the deformation behaviour with respect to the acoustic emission response and mechanical properties of differently extruded magnesium Mg-Mn alloys. Six types of Mg-Mn alloys (with Al, Ca, Ce, Y, Nd additions) were processed by indirect extrusion with two different speeds. Alloys with addition of Ca, Al and Nd were selected and presented in this manuscript due to their prospective mechanical properties. Additions of Ca and Al had significant influence on the microstructure refinement and texture of the Mg-Mn alloy, whereas addition of Nd led to the absence of the tension-compression asymmetry. Measurements of the acoustic emission were done during the uniaxial tension and compression tests. The results are discussed with respect to the influence of alloying elements on the deformation behaviour in terms of the activation of dislocation glide and twinning.

Effect of Nd Additions on Extrusion Texture Development and on Slip Activity in a Mg-Mn Alloy

Two Mg-1 wt pct Mn alloys containing 0.5 wt pct and 1 wt pct Nd have been processed by indirect extrusion at temperatures ranging from 548 K (275 °C) to 633 K (360 °C) and speeds between 2.8 and 11 mm/s. The microstructure and the texture of the extruded bars were analyzed in order to understand the effect of the processing parameters and of the rare-earth (RE) alloying additions on the texture development. Increasing the Nd content results in weak textures in which the predominant orientations are a function of the extrusion conditions. This may be explained by the occurrence of particle pinning of grain boundaries and by the nucleation of grains with a wider range of orientations. Mechanical tests were carried out in tension and in compression in all the processed samples at 10−3 s−1 and room temperature. It was found that larger RE amounts give rise to the disappearance of the yield asymmetry and to an anomalously high activity of tensile twinning, especially at the lowest extrusion temperatures. This has been attributed to an increase of the critical resolved shear stress of basal slip due to the presence of Mg3Nd coherent and semi-coherent intermetallic prismatic plates.

Hot compression deformation characteristics of Mg-Mn alloys

The hot deformation behaviors of solution treated Mg-1.8Mn-0.4Er-0.2Al alloys were investigated by means of compression tests on Gleeble-1500 in strain rate range of 0.01-10 s −1, deformation temperature range of 250–450 °C and a true strain of 0.6. The constitutive relationships among flow stress, strain rate and deformation temperature were described by Arrhenius-type equations, based on the fact that the material constants could be calculated under a wide range of strains. The results show that the flow stress of the experimental alloy decreases with temperature increasing and strain rate decreasing. Under the experimental conditions, the products of constant a and n in the constitutive equation are stable within certain strains, and the deformation activation energy ranges from 160 to 220 kJ/mol. It is proved that the values of calculated flow stress are close to the experimental results with average error of 2.01%.

Effect of Zn on mechanical property and corrosion property of extruded Mg-Zn-Mn alloy

The effect of Zn on the microstructure, the mechanical property and the corrosion property in simulated body fluid(SBF) of an extruded Mg-Mn alloy was studied. The results indicate that the addition of Zn element can significantly refine the grain size of the extruded Mg-Mn alloy. When Zn content is increased from 0% to 3%, the grain size decreases from 12 μm to 4 μm. Meanwhile, the mechanical properties also increase remarkably with increasing Zn content. When Zn content is 3%, the ultimate tensile strength and the yield strength are increased by 54.7 MPa and 69.7 MPa, respectively. Zn can also improve the anti-corrosion property of the alloy. The best anti-corrosion property is obtained with 1% Zn. However, further increase of Zn content up to 3% deteriorates the corrosion property. Finally, the influence mechanism of Zn on the microstructure, the mechanical property and the corrosion property was discussed.

The Microstructures of As-Cast Mg-Zr and Mg-Mn Alloys

The as-cast microstructures of two dilute Mg-Zr and three dilute Mg-Mn alloys were studied using optical microscopy and scanning electron microscopy, including EDX analysis. The results show that the as-cast microstructure of the Mg-Zr alloys was composed of non-dendritic, equiaxed Mg grains, with a few Zr particles within the Mg grains and along grain boundaries. The grain size of the Mg-Zr alloy was significantly reduced by the Zr addition and a fine grain structure was achieved when the zirconium concentration was above 0.4wt. %. The as-cast structure of the Mg- Mn alloys contained columnar, dendritic grains. Two types of Mn particles (equiaxed large particles and rod-like or plate-like small particles) were observed in the as-cast Mg-Mn alloys. The volume fraction of particles and the size differences between the large and small particles increased with an increase of Mn concentration.

Investigation on Microstructures of Heat Treated Mg-Zr and Mg-Mn Alloys

The microstructure of three dilute Mg-Mn and two dilute Mg-Zr alloys which had been heat treated at different temperatures and times were studied using optical microscopy and various electron optical techniques, including FEGSEM and TEM. It was found that the Mg-Zr alloys homogenized at 500°C and annealed at 350°C contained a fine dispersion of Zr-containing particles at grain boundaries and within grains. In contrast, annealing Mg-Zr alloys at 300°C for up to 3 h led to little modification of the as-cast structures. When the Mn content was less than 0.9 weight percent, homogenization of the Mg-Mn alloys at 550 to 600°C resulted in the dissolution of small rod-like and needle-shape particles, which then grown up as fine particles when aged at 300°C. Mg- 0.6Mn and Mg-0.9Mn alloys annealed at 300 to 400°C without solution treatment contained a large volume fraction of nano-sized precipitates.

Extraction of second phases from magnesium and aluminum alloys for analytical electron microscopy.

Techniques are described for the extraction onto carbon replicas of precipitates and inclusions from Mg and Al-based alloys for analytical transmission electron microscopy. EDX analysis of Mn precipitates from a Mg-Mn alloy illustrates the problems that can arise from spurious X-rays, caused by the use of a 3mm disc specimen.

Spin-glass transition in Mg[sbnd]Mn alloys

A spin-glass transition as evidenced by a susceptibility peak and irreversibility was discovered in h.c.p. MgMn alloys with a Mn content ranging from 5 to 50 at. % Mn. The spin-freezing temperatures range from 5 to 25 K.

Low-Temperature Magnetoresistance in Magnesium and Aluminum Containing Small Concentrations of Manganese or Iron

Magnetoresistance measurements in magnetic fields up to 21 kOe have been made on Mg-Mn, Mg-Cd, Mg-Al, Al-Mn, and Al-Fe alloys in the temperature region of liquid helium. Magnesium alloys containing more than 0.1-at.% Mn which exhibit a resistance maximum and minimum in zero field, show a negative magnetoresistance, whereas the more dilute samples (0.001-0.1 at.% Mn) show a positive magnetoresistance, the magnitude of which decreases with decreasing temperature. The magnesium alloys containing nontransition element impurities, as well as the aluminum alloys containing transition metal impurities, are found to obey Kohler's rule. From an analysis of these data it is found that the magnetoresistivity of a dilute alloy of magnesium containing manganese, can be considered as the sum of a normal positive magnetoresistivity (obeying Kohler's rule) and an anomalous term which is negative in sign, does not obey Kohler's rule and is presumably due to a magnetic scattering of the conduction electrons. Using values of the $s\ensuremath{-}d$ exchange integral and the Coulomb scattering integral derived from an analysis of the zero-field resistivity permits an explanation of the magnetoresistivity based on Kasuya's theory, at temperatures near the N\'eel point.

Plastic deformation of Mg-Mn alloy single crystals

Strengthening in the early aged state is attributed to a shear of thin α-Mn precipitate particles by dislocations which produces chemical hardening and generates new faulted interfaces inside the manganese particles. Activation energies and volumes have been calculated for this process from the dependence of the flow stress on temperature and strain rate. The temperature dependence of the flow stress as a function of strain shows that the dislocation friction stress due to precipitates is small. The solid solution strength is attributed to clustering. A number of analogies are made with the case of hardening due to GP-I zones in Al-Cu alloys. Geometrical softening yield points, previously found at 300°K, are suppressed at 77°K by the increased rate of work hardening at the lower temperature.

Low-Temperature Magnetic Properties of Dilute Mg-Mn, Al-Mn, Mg-Fe, and Al-Fe Alloys

Magnetic susceptibility measurements are reported on some dilute alloys of Mg-Mn and Al-Mn in the temperature range, room temperature -1.3\ifmmode^\circ\else\textdegree\fi{}K. Electron spin resonance (ESR) absorption has been observed in the magnesium alloy containing 0.6 at.% manganese and studied as a function of temperature. Room temperature magnetic susceptibility measurements and low temperature ESR experiments are reported for Mg-Fe and Al-Fe alloys. The concentration dependence of the Curie constant at high temperature suggests the presence of four unpaired electrons for the manganese atom dissolved in magnesium. Similar information concerning manganese dissolved in aluminum suggests one unpaired electron if a completely localized $d$ state is formed.The susceptibility of dilute Mg-Mn alloys shows departures from a Curie law, which could be interpreted as an increase in the spin state of the manganese ion in the region of the resistance minimum. This excess paramagnetism is discussed in terms of the possible mechanisms which could produce a resistance minimum and leads to the conclusion that if there is a ferromagnetic coupling between randomly distributed manganese pairs, the interaction mechanism operates over approximately 10 lattice spacings.The effective magneton number of Mn in the more dilute Mg-Mn alloys also increases with temperature at high temperatures. The susceptibility of the concentrated Mg-Mn alloy obeys a Curie law except in the region of the resistance maximum where both susceptibility and ESR data indicate an antiferromagnetic transition.The influence of the low-temperature transition, occurring in the magnesium alloy containing about 0.6 at.% manganese, on the electron spin resonance linewidth and magnetic field value has been measured as a function of temperature giving $g$ values of 2.01\ifmmode\pm\else\textpm\fi{}0.01 above 6\ifmmode^\circ\else\textdegree\fi{}K. The shift of the position of resonance field below 6\ifmmode^\circ\else\textdegree\fi{}K is consistent with antiferromagnetic behavior in Mg-Mn. The line shift is proportional to ${T}^{\ensuremath{-}1}$ in the antiferromagnetic region which would be consistent with a conduction electron superexchange mechanism for the antiferromagnetic manganese ion interaction. The linewidth is broadened in the region of the resistance minimum and attains a constant value as the temperature is lowered. This behavior is consistent with localized spin interactions, giving rise to larger averaged spin values in the resistance minimum region as suggested from the magnetic susceptibility studies of the more dilute alloys.

Study on zirconium containing magnesium casting alloy (9th Report)

This is to report on the tests on anti-corrosion of pure magnesium, Mg-RE, Mg-Zn, Mg-RE-Zn, EK30, EZ33, ZK51, AZ63, AZ92, A10 and Mg-Mn alloys. Under these tests, the specimens of the above alloys were dipped into the solutions of 0.06 N HCl and 1N NaCl plus 3% H2O, and quantity of gas generated from the specimens by corrosion was measured.It was found out that the magnesium alloys containing Zirconium have better anti-corrosion properties than ordinary Mg-Al-Zn-Mn alloys. This is due probably to the fact that magnesium is purified and the contained iron is excluded by Zirconium.Subsequent experiments were made for finding out the anti-corrosive effects of various chemical treatments on magnesium alloys. The bath was prepared with solutions of 15% potassium dichromate, 0.5% hydrochloric acid, 5% nitric acide, which were kept under the temperature of 40°C.It was found out from the above experiments that the Mg-RE-Zn alloy shows good corrosion resistance, while the above chemical treatments can not improveits anti-corrosion properties.