Pct Mn Alloy Research Articles

Compressive and Corrosion Properties of Lotus-Type Porous Mg-Mn Alloys Fabricated by Unidirectional Solidification

Lotus-type porous Mg-Mn alloys were fabricated by solid-gas eutectic unidirectional solidification (the Gasar process) by controlling and optimizing the process parameters. The microstructures, compressive properties and corrosion properties in a simulated body fluid solution were investigated. Porous pure Mg was prepared with a preferentially oriented (11$$ \bar{2} $$2) plane, whereas the Mg-2 wt pct Mn alloy showed a preferentially oriented (10$$ \bar{1} $$3) plane. Mn addition refined the grains, improved the Mn precipitates, activated the {10$$ \bar{1} $$2} twin at the end of the pores and increased the compressive strength from 64 MPa for pure Mg to 74 MPa for 1 wt pctMn and 80 MPa for 2 wt pct Mn. Electrochemical tests showed that 2 wt pct Mn addition could decrease the corrosion current from 1.84 × 10−3 to 4.22 × 10−4 A cm−2. Immersion tests suggest that 2 wt pct Mn addition reduced the sample mass loss, which indicated a better corrosion performance, and exhibited a smaller decrease in compressive strength compared with that of the porous pure Mg. This work shows that the Gasar technique can be a promising fabrication method to prepare lotus-type porous Mg-Mn alloys which are more attractive for application in degradable biomaterials engineering.

Creep Behaviors of Two Near-Eutectic Al-Si-Cu-Mn Heat-Resistant Alloys Containing Dendritic Mn-Rich Primary Phase or Modified Star-Like Cr-Mn-Rich Primary Phase

In this study, the creep responses of two near-eutectic Al-Si-Cu-Mn alloys, Al-12wt pctSi-4 pctCu-1.2wt pctMn alloy (Alloy-1, containing dendritic Mn-rich primary phase) and Al-12wt pctSi-4 pctCu-2wt pctMn-1wt pctCr alloy (Alloy-2, containing star-like Cr-Mn rich primary phase), were investigated from 448 K to 523 K at 40 to 70 MPa applied stress. Results show that with 100 hours of exposure at 448 K/40 to 70 MPa, true steady-state creep was not attained. However, at 473 to 523 K/40 to 70 MPa, both the alloys showed a fixed creep rate establishing steady-state creep. The creep curves of the studied alloys illustrate that Alloy-1 exhibits lower creep rates and less creep strains than Alloy-2 in each combination of temperature and applied stress. Considering the creep rates and total creep strains after 100 hours of exposure, Alloy-1 possesses much better creep resistance than Alloy-2, even though the high-temperature strength of Alloy-2 is higher than that of Alloy-1 at 448 K and 523 K. Higher strength at high temperatures does not mean high creep resistance at high temperatures. At low to moderately high temperatures (0.48 to 0.53 Tm where Tm is the equilibrium melting point of pure Al in K) and applied stress of 40 to 70 MPa, the creep mechanisms in Alloy-1 and Alloy-2 are similar and diffusion is the rate-controlling process.

Analysis of Hot- and Cold-Rolled Loads in Medium-Mn TRIP Steels

The purpose of this work is to investigate the hot- and cold-rolling requirements to produce third-generation advanced high-strength steels (AHSS). Therefore, five medium-Mn (10 to 14 wt pct Mn) alloys that exhibit transformation-induced plasticity (TRIP) were compared to a commercially produced grade of AISI 1018 using hot- and cold-rolling experiments. Experimental data collected from a STANAT instrumented rolling mill was utilized to measure force and torque during hot- and cold-rolling. Experimental data were processed by a 1D analytical model, based on Orowan model, to determine rolling pressure. It was determined that pressures required to hot-roll TRIP alloys are 1.4 to 1.8 times greater than pressures for rolling AISI 1018 steel. Cold rolling of the medium-Mn TRIP steels was found to be 1.5 to 2.8 times greater than the AISI 1018 steel. Mechanical and microstructural characterization was also performed and the variation in rolling pressure was related to the starting microstructural constituents, and alloys containing greater starting quantities of e-martensite in the microstructure had higher flow stresses at equivalent rolling strains during cold rolling.

Effect of Mn and C on Grain Growth in Mn Steels

Grain growth in Fe-Mn austenites was examined at 1373 K and 1473 K as a function of Mn (0 to 30 wt pct) and carbon (0 to 0.5 wt pct) content. The addition of Mn had the effect of reducing the rate of grain growth. The observed inhibiting effect of Mn is believed to be mainly due to an increase in the occurrence of annealing twins with increasing Mn content. It is hypothesized that, upon intersecting with High-Angle Grain Boundaries (HAGBs), the twins result in low-energy, low-mobility boundary segments which ultimately slow the overall growth kinetics. Solute drag does not appear to significantly contribute to the slowing of the grain growth kinetics for Mn contents greater than 6 wt pct. Atom probe tomography studies confirmed weak or negligible segregation of Mn to HAGBs. The carbon content had a small but measurable effect on the grain growth kinetics. Reduction of the carbon content in an Fe-30 wt pct Mn alloy resulted in a decrease in effective grain boundary mobility.

Orientation of Magnetized MnBi in a Strong Static Magnetic Field

Solidification of Bi-4.5 wt pct Mn alloy was investigated in the presence and absence of a strong static magnetic field (SSMF). A cooling rate (R) of 60 K/min caused MnBi to orient with the SSMF, owing to the force moment and attractive force. The attractive force and magnetic gradient force induced formation of multilayered MnBi when R was 5 K/min. The magnetic gradient force was damped when R was 60 K/min. Low cooling rates favored the aggregation process.

Morphological Stability of δ-Ferrite/γ Interphase Boundary in Carbon Steel

The morphological changes of the δ-ferrite/γ interphase boundary have been observed in situ with a high-temperature confocal scanning laser microscope (HTCSLM) during δ/γ transformations (δ → γ and γ → δ) of Fe-0.06 wt pct C-0.6 wt pct Mn alloy, and a kinetic equation of morphological stability of δ-ferrite/γ interphase boundary has been established. Thereafter, the criterion expression for morphological stability of δ-ferrite/γ interphase boundary was established and discussed, and the critical migration speeds of δ-ferrite/γ interphase boundaries are calculated in Fe-C, Fe-Ni, and Fe-Cr alloys. The results indicate that the δ-ferrite/γ interphase boundary is very stable and nearly remains absolute planar all the time during γ → δ transformation in Fe-C alloy. The δ-ferrite/γ interphase boundary remains basically planar during δ → γ transformation when the migration speed is lower than 0.88 μm/s, and the interphase boundary will be unstable and exhibit a finger-like morphology when the migration speed is higher than 0.88 μm/s. The morphological stability of δ-ferrite/γ interphase boundary is primarily controlled by the interface energy and the solute concentration gradient at the front of the boundary. During the constant temperature phase transformation, an opposite temperature gradient on both sides of δ-ferrite/γ interphase boundary weakens the steady effect of the temperature gradient on the boundary. The theoretical analysis of the morphological stability of the δ-ferrite/γ interphase boundary is coincident with the observed experimental results utilizing the HTCSLM. There is a good agreement between the theoretical calculation of the critical moving velocities of δ-ferrite/γ interphase boundaries and the experimental results.

Predicting Pathways for Synthesis of Ferromagnetic τ Phase in Binary Heusler Alloy Al-55 pct Mn Through Understanding of the Kinetics of ε–τ Transformation

This paper outlines the detailed procedure for the synthesis of pure ferromagnetic tau phase in binary Heusler Al-55 pct Mn alloy in bulk form through casting route without any addition of stabilizers. To obtain the processing domain for the formation of the tau phase from high-temperature epsilon phase, isothermal transformation experiments were carried out. The structure and microstructure were characterized by X-ray diffraction and electron microscopy studies. The tau phase start times were obtained through magnetic measurements. In order to tune the casting conditions for the formation of this phase, thermal modeling was carried out to predict the heat extraction rates for copper molds of different diameters (2 to 12 mm) containing hot solids during casting process. This enabled us to estimate the diameter of the mold to be used for obtaining tau phase directly during casting. It was concluded through experimental verification that 10-mm-diameter casting in copper mold is suitable to obtain complete tau phase. A saturation magnetization of 116 emu/g at 10 K was measured for such samples. The Curie point for the tau phase was found to be 668 K (395 A degrees C). Additionally, the cast rod exhibits a compressive strength of 1170 MPa which is higher than those of both ferrites and AlNiCo magnets.

Thermodynamic Driving Force of the γ → ε Transformation and Resulting MS Temperature in High-Mn Steels

Two-stage transformation-induced plasticity (TRIP) behavior characterized by the martensitic transformations, γ → e → α′, has produced exceptional tensile strengths and work hardening rates in Fe-14 wt pct Mn alloys containing Al and Si. A regular solution model has been developed to accurately calculate ΔG γ → e for a given TRIP alloy and the calculated driving force is used to determine the M S e temperature. The regular solution model developed here predicted driving forces that corresponded well with reported microstructures and behavior of seven FeMnAlSiC steels from literature when considered in conjunction with nucleating defect critical size and material process history. The role of available nucleating defects of critical size, n*, has been linked to the stacking fault energy necessary to observe the γ → e transformation and the M S e temperature. The regular solution model provided excellent correlation between calculated M S e temperatures and those measured experimentally in 89 alloys from literature and suggested n* = 4 is the critical size of a nucleating defect in annealed microstructures. Factors affecting the γ → e transformation and the M S e temperature have been identified as prior austenite grain size, dislocation substructure due to prior deformation, and solute segregation.

Influence of the Thermomechanical Treatment on the Intergranular Corrosion Susceptibility of Zn-Modified Al-5.1 Wt Pct Mg-0.7 Wt Pct Mn Alloy Sheet

In this study, the effect of thermomechanical treatment on intergranular corrosion (IGC) susceptibility of the Zn-modified Al-5.1 wt pct Mg-0.7 wt pct Mn alloy plates was investigated. The specimens underwent varied amounts of cold work, while final annealing was conducted in the 493 K to 533 K (220 °C to 260 °C) temperature range. It was shown that the extent of cold work, especially at lower temperatures of treatment, had a profound effect on the corrosion resistance of the alloy. Such observation was in direct correlation with the morphology of precipitated ternary grain boundary phase (Al-Mg-Zn). Microstructural characterization showed that, depending on the amount of cold work, different deformation substructures were created, which, in turn, influenced kinetics and the mechanism of precipitation. Wetting of the grain boundaries by the ternary grain boundary phase (Al-Mg-Zn) was a signature of the IGC susceptible state and occurred in the specimens that were subjected to a lower degree of cold work. The specimens that underwent a higher degree of cold work (over 30 pct) showed superior corrosion resistance as a result of ternary grain boundary phase (Al-Mg-Zn) precipitation in the form of discrete particles at the grain boundaries as well as in grain interiors.

Three Dimensional Morphology of Mn Rich Intermetallics in AlSi Alloys Investigated with X-Ray Tomography

Elementary Mn has a great importance as neutralizer of Fe intermetallics like β-Al5FeSi, which have detrimental effect on mechanical characteristics of AlSi alloys. Presence of Mn in AlSi alloys causes the formation of other intermetallic phases. To understand the effect of solidification conditions and fluid flow on the microstructure of AlSi-based alloys and the addition of Mn leading to Mn-based intermetallics, Al-5 wt pct Si 0.2/0.4/1.0 wt pct Mn alloys have been directionally solidified under defined thermal (gradient 3 K/mm, solidification velocity 0.02-0.12 mm/s) and fluid flow (rotating magnetic field 6 mT) conditions. The primary Al-phase and Mn-based intermetallic phases were studied using 3D X-ray tomography. The spatial morphology of primary phase and intermetallics were characterized with respect to different fluid flow and solidification conditions. The tomography has showed the 3D complicated structure of Mn phases developed.

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.

Dynamics Study on Morphological Stabilities of Cellular Crystal Lateral Wall

The lateral wall stabilities during the growing process of cellular crystal in the melt were studied in this article. The dynamics equation of cylindrical solid-liquid interface morphological stabilities in melt was first derived, and then the expression of criterion for cylindrical solid-liquid interface morphological stabilities was defined. The effect of the shape factor, solid radius, and other relevant factors on the morphological stabilities was analyzed. Also, the critical shape factor and critical growth rate for keeping the stabilities of the interface were determined. The phenomenon during the lateral growth process of δ-phase cellular crystal in carbon steel was observed under a high-temperature confocal scanning laser microscope (HTCSLM), which was used to verify the theoretical analysis and calculated results. The results indicate that the shape factor is beneficial to improving the stabilities of the cellular crystal lateral wall. During the increase process of the cellular crystal radius, however, there is a certain value of the cellular crystal radius, which induces the shape factor to reduce stabilities of the cellular crystal lateral wall rapidly. Even if the other conditions are unchanged, the shape of the cellular crystal may also cause the cellular crystal lateral wall to lose its stabilities. There are two critical growth rates to keep the cellular crystal lateral wall growing stably under the conditions of this research. For the Fe-0.15 pct C-0.8 pct Mn alloy, these two critical growth rates are 10−4 and 10 cm/s orders of magnitude, respectively. The difference between them is more than 105 times, so the slow critical growth rate conforms to the actual critical growth rate. The radius of the cellular crystal is the main influencing factor of lateral wall stabilities. The bigger the radius of the cellular crystal is, the worse the stabilities of the lateral wall are. That is also one of the reasons that the fine cellular crystal can survive during a certain period. The results of the theoretical analysis about stabilities of the cellular crystal lateral wall agree well with the lateral growth phenomena of δ phase cellular crystal in carbon steel observed by a HTCSLM. The theoretically calculated results of the radial critical growth rates are coincident with the experimental results.

Superplastic behavior and microstructure evolution in a commercial Al-Mg-Sc alloy subjected to intense plastic straining

A commercial Al-6 pct Mg-0.3 pct Sc-0.3 pct Mn alloy subjected to equal-channel angular extrusion (ECAE) at 325 °C to a total strain of about 16 resulted in an average grain size of about 1 µm. Superplastic properties and microstructural evolution of the alloy were studied in tension at strain rates ranging from 1.4 × 10−5 to 1.4 s−1 in the temperature interval 250 °C to 500 °C. It was shown that this alloy exhibited superior superplastic properties in the wide temperature range 250 °C to 500 °C at strain rates higher than 10−2 s−1. The highest elongation to failure of 2000 pct was attained at a temperature of 450 °C and an initial strain rate of 5.6 × 10−2 s−1 with the corresponding strain rate sensitivity coefficient of 0.46. An increase in temperature from 250 °C to 500 °C resulted in a shift of the optimal strain rate for superplasticity, at which highest ductility appeared, to higher strain rates. Superior superplastic properties of the commercial Al-Mg-Sc alloy are attributed to high stability of ultrafine grain structure under static annealing and superplastic deformation at T ≤ 450 °C. Two different fracture mechanisms were revealed. At temperatures higher than 300 °C or strain rates less than 10−1 s−1, failure took place in a brittle manner almost without necking, and cavitation played a major role in the failure. In contrast, at low temperatures or high strain rates, fracture occurred in a ductile manner by localized necking. The results suggest that the development of ultrafine-grained structure in the commercial Al-Mg-Sc alloy enables superplastic deformation at high strain rates and low temperatures, making the process of superplastic forming commercially attractive for the fabrication of high-volume components.

Application of electromagnetic separation of phases in alloy melt to produce In-situ surface and functionally gradient composites

The principle of electromagnetic separation of phases (primary phase) in alloy melt is that the electromagnetic force scarcely acts on the primary phases due to its low electric conductivity as compared to the melt. As a result, a repulsive force acts on the primary iron-rich phases to push them to move in the direction opposite to that of the electromagnetic force. The in-situ surface composite and the functionally gradient composite reinforced by primary Si are produced when the hypereutectic Al-Si alloy solidifies under electromagnetic force induced by static magnetic field and DC current. Similarly, the Al-Si-1.20 pct Fe-1.60 pct Mn alloy in-situ surface composite reinforced by primary iron-rich phase is produced. Based on this, a new method for production of in-situ multigradient composite with several layers, by electromagnetic separation of phases and directional solidification technique, is proposed.

Relationship between austenite dislocation density introduced during thermal cycling and M s temperature in an Fe-17 wt pct Mn alloy

The reason why thermal cycling decreases the martensite start (M s ) temperature of an Fe-17 wt pct Mn alloy was quantitatively investigated, based on the nucleation model of e martensite and a thermodynamic model for a martensitic transformation. The M s temperature decreased by about 22 K after nine cycles between 303 and 573 K, due to the increase in shear-strain energy (ΔG sh ) required to advance the transformation dislocations through dislocation forests formed in austenite during thermal cycling. The ΔG sh value increased from 19.3 to 28.8 MJ/m3 due to the increase in austenite dislocation density from 1.5 × 1012 to 3.8 × 1013/m2 with the number of thermal cycles (in this case, up to nine cycles). The austenite dislocation density increased rapidly for up to five thermal cycles and then increased gradually with further thermal cycles, showing a good agreement with the increase in austenite hardness with the number of thermal cycles.

Movement of γ/ε interfaces and coalescence of ε martensite variants under the tensile stress in an Fe-24 Wt Pct Mn alloy

This study was pursued to investigate the movement of γ/e interfaces and the coalescence of e martensite variants in an Fe-Mn binary system. An Fe-24 wt pct Mn tensile specimen was deformed with increasing tensile strain at room temperature. The microstructural changes at a fixed area of the tensile specimen were continuously observed using an optical microscope. Some of the γ/e interfaces moved forward due to γ → e transformation, and the others moved backward due to its reverse transformation during the tensile deformation, depending on the orientation relationship between the tensile direction and each e variant. The coalescence of e martensite variants primarily occurs by the following three factors: (1) the reverse transformation of e variants under an applied stress having a different direction from that of the e variants’ shape change, (2) the nucleation and growth of new e variants under an applied stress having the same direction as that of the e variants’ shape change, and (3) the continuous growth of pre-existing e variants under an applied stress having the same direction as that of the e variants’ shape change.

Effects of thermal cycling on the kinetics of the γ → ε martensitic transformation in an Fe-17 wt pct Mn alloy

The thermal cycling of an Fe-17 wt pct Mn alloy between 303 and 573 K was performed to investigate the effects of thermal cycling on the kinetics of the γ → e martensitic transformation in detail and to explain the previous, contrasting results of the change in the amount of e martensite at room temperature with thermal cycling. It was observed that the shape of the γ → e martensitic transformation curve (volume fraction vs temperature) changed gradually from a C to an S curve with an increasing number of thermal cycles. The amount of e martensite of an Fe-17 wt pct Mn alloy at room temperature increased with thermal cycling, in spite of the decrease in the martensitic start (M s) temperature. This is due to the increase in transformation kinetics of e martensite at numerous nucleation sites introduced in the austenite during thermal cycling.

Effect of deformation on the damping capacity in an Fe-23 pct mn alloy

Effect of deformation on the damping capacity in an Fe-23 pct mn alloy

Simplified computation of macrosegregation in multicomponent aluminum alloys

An approximate method for calculating the macrosegregation in a multicomponent aluminum alloy is proposed. This method is based on the use of a predefined solidification path (i.e., relation between the solute concentration in the liquid phase and the solid fraction) instead of addressing the fully coupled micro-macrosegregation problem. In determining the solidification path, it is assumed that the total solute concentration is constant, and that the solidification history is the same everywhere in the casting. In this manner it becomes quite easy to take into account how the macrosegregation development is affected by the solute diffusion in the dendrites and the precipitation of secondary phases, provided that such effects are accounted for in the model used for determining the solidification path. In order to demonstrate the approximate method, the inverse segregation formation at a chill surface of an Al-4 pct Mg-0.2 pct Fe-0.15 pct Si-0.3 pct Mn (AA5182) alloy is calculated. In this case study, the solidification path is determined prior to the macrosegregation computation by a microsegregation model discussed elsewhere, and the solid and liquid densities are related to the concentrations of the different alloying elements by a simple mixture law without distinguishing between the different solid phases that are formed. The accuracy of the approximate method is discussed by considering a binary alloy. It turns out that the macrosegregation formation at a chill surface of an Al-4 pct Mg alloy is fairly close to that resulting from a modeling in which the variation of the total solute concentration is taken into account. Furthermore, the mixture law is compared to a more elaborate treatment of the densities involving both primary and eutectic solid phases. This comparison is carried out for an Al-4.5 pct Cu alloy for which literature data exist. The mixture law is found to give a reasonable accuracy in the calculated macrosegregation.

Evolution of microstructure and tensile strength of rapidly solidified Al-4.7 pct Zn-2.5 pct Mg-0.25 pct Zr-X wt pct Mn alloys

Analytical transmission electron microscopy and thermal analysis of as-extruded Al-4.7 pct Zn-2.5 pct Mg-0.2 pct Zr-X wt pct Mn alloys, with Mn contents ranging from 0.5 to 2.5 wt pct, were carried out to elucidate the microstructural change and accompanying mechanical properties during subsequent heat treatments. The as-extruded alloy was fabricated from rapidly solidified powder and consisted of a fine, metastable manganese dispersoid and the ternary eutectic T phase (Al2Mg3Zn3). Solution heat treatment resulted in the formation of the stable Al6Mn phase and complete dissolution of the T phase. Formation of stable Al6Mn was made by two routes: by phase transition from metastable Mn dispersoids which already existed, and from the supersaturated solid solution by homogeneous nucleation. The density of the Al6Mn phase increased with the addition of manganese, while the shape and average size remained unchanged. A significant increase in the hardness was observed to coincide with the formation of the Al6Mn phase. Similarly, the tensile strength increased further after the aging treatment, and the increment was constant over the content of Mn in the alloy, which was explained by the contribution from the same amount of precipitates, MgZn2. Results of thermal analysis indicated that the dissolution of the T phase started near 180 °C and that formation of Al6Mn occurred at about 400 °C, suggesting that further enhancement of strength is possible with the modification of the heat-treatment schedule.