Al-Mn Alloys Research Articles

Substantiation of Experimentally Observed Self-Accommodation Complexes of Martensite Crystals in Alloys with Shape Memory Effects

This paper presents an algorithm for analyzing the possibility of the formation of self-accommodation complexes of martensite crystals in alloys with shape memory effects with consideration for twinning and minimization of the strain averaged over a corresponding set of domains. It has been shown that complete self-accommodation is possible only in the complexes that simultaneously contain all the orientation relationship variants. The calculation performed for the case of rhombohedral martensite (four possible orientation relationship variants) has demonstrated that there is no average shape strain in the four domains. The thus-formed four-domain complex incorporates all the possible variants of the orientation relationship and, for this reason is a self-accommodation complex. Such complexes have been repeatedly observed in titanium nickelide alloys. The analysis of monoclinic 18R-martensite shows that complete self-accommodation can be attained only in the complex of 12 different domains. The experimentally observed four-domain complexes in the Cu—Al—Ni and Cu—Al—Mn alloys can be explained by partial self-accommodation, which takes the exposure of a martensite crystal on the outer surface of a crystal into account.

Characterization of the metallic phase and the slag phase obtained during the inertization of the cathodes of spent alkaline batteries using liquid aluminum

In this work, a reactive melting procedure was implemented for the inertization of the manganese-containing cathodes of spent alkaline batteries. The process consisted of adding the cathode powder mixed with borax on top of molten aluminum at 1000 °C. By means of an aluminothermic reaction, manganese oxides are reduced and incorporated into the alloy. The presence of borax in the reactive mixture was found to be fundamental to obtain the Al-Mn alloy. The characterization of the metal phase and the slag phase by scanning electron microscopy and X-ray diffraction showed that manganese is reduced to form manganese borides in the slag and Al-Mn intermetallics in the alloy. This process could make feasible to use aluminum casting shops as processors of spent alkaline batteries.

Investigation of phase selection hierarchy in Mn–Al alloys

Primarily attributed to the formation of the ferromagnetic τ-phase, near equiatomic composition of Mn–Al have recently received much attention in permanent magnet industry. Several mechanisms have been proposed in literature for the τ-phase formation but controversy still arises regarding the dominating mode. In the current work, MnAl-based alloys having different compositions in a range between Mn50.5Al49.5 and Mn57Al43 have been studied by means of in-situ high energy X-ray diffraction, differential scanning calorimetry (DSC) and magnetic measurements. Synchrotron and DSC experiments showed the dependence of the τ-MnAl on the intermediate disordered ε′-phase. Alloys having 53.4 at% or less Mn (S1, S2) followed a transformation route of ε+ε'→τ→β+γ2 upon annealing. Alloys having more than 53.4 at% of Mn had only ε-phase. High energy X-ray diffraction patterns showed that ε-phase directly transformed into stable phases in the absence of ε′-phase. It is observed that ε′ not only promoted the ferromagnetic τ-phase but also stabilized it by delaying the nucleation of stable phases.

Production of net-shape Mn-Al permanent magnets by electron beam melting

The main goal of this work is the adoption of additive manufacturing for the production of inexpensive rare-earth free MnAl-based permanent magnets. The use of more advanced binder-free additive manufacturing technique such as Electron Beam Melting (EBM) allows obtaining fully-dense magnetic materials with advanced topology and complex shapes. We focus on the feasibility of controlling the phase formation in additively manufactured Mn-Al alloys by employing post-manufacturing heat treatment. The as-manufactured EBM samples contain 8% of the desired ferromagnetic τ-MnAl phase. After the optimized annealing treatment, the content of the τ-phase was increased to 90%. This sample has a coercivity value of 0.15 T, which is also the maximum achieved in conventionally produced binary MnAl magnets. Moreover, the EBM samples are fully dense and have the same density as the samples produced by conventional melting density.

High Coercivity in MnAl Disc Prepared by Severe Plastic Deformation

The low coercivity in MnAl alloys has become a barrier to develop high performance MnAl‐based magnets for more than five decades. Herein, a high room‐temperature coercivity of 0.59 T in MnAl disc is achieved by severe plastic deformation. The grain size of the MnAl decreases significantly when ε‐phase is transformed into τ‐phase and when the τ‐phase is severely deformed. The aging process enhances the magnetization of the deformed τ‐phase significantly and reduces the coercivity of the MnAl disc to 0.396 T. The magnetic domain structure of the severely deformed τ‐MnAl exhibits many pinning sites in the intergranular regions and within the domains, resulting in the high coercivity of the bulk samples. The deformation process produces locally oriented texture of τ‐phase. This study opens a window for development of MnAl‐based bulk magnet with high coercivity and enhanced remanence.

Improved strength and enhanced pitting corrosion resistance of Al-Mn alloy with Zr addition

Abstract Automotive heat exchanger materials with high strength and excellent corrosion resistance performance are highly required due to the increasing demands of weight reduction and fuel economy. In this work, 0.16 wt% Zr was added into a Al-1.5Mn-0.3Fe-0.6Si-0.5Cu(wt.%) alloy for the improvement of the related performance. The microstructure, mechanical properties and electrochemical properties were investigated. The results indicate that Zr addition can decrease grain size and increase the volume fraction of low angle boundaries (LAGBs) in the alloy. The improved strength derives from finer grain sizes and Al3Zr particle. The enhanced pitting corrosion resistance mainly results from the higher volume fraction of LAGBs and smaller grain sizes.

Highly localized shear deformation in a Mg–Al–Mn alloy subjected to ballistic impact

Shear localization, which might result in the formation of shear bands in materials, is considered as a dominating deformation mechanism in materials under dynamic loading. In the present study, the microstructures of twin-induced ASBs in a Mg–Al–Mn alloy under ballistic impact were studied using scanning electron microscope and transmission electron microscope to investigate the localized shear deformation behavior of Mg alloys under high strain rate deformation. The results show that highly localized shear deformation mainly occurs at the boundary regions of deformed twins, resulting in the formation of narrow shear bands. The twin-induced ASBs composed of fine recrystallized grains and Mg17Al12 precipitates, while the internal part of twins shows the microstructure with elongated grains. The initiation of ASBs at the twin boundary regions is mainly attributed to the stress concentration at twin boundaries due to the dislocation pile-up. These results can contribute to further understanding of the shear deformation behavior of Mg alloys under dynamic loading.

Microstructure Evolution and Its Effect on Magnetic Properties of Mn-Al Alloy Fabricated via End Milling Machining Process

Microstructure Evolution and Its Effect on Magnetic Properties of Mn-Al Alloy Fabricated via End Milling Machining Process

Cold arc cladding of aluminum coatings on AZ61 magnesium alloy: A comparative study

The corrosion resistance and wear resistance of magnesium alloys seriously restrict their applications in industry. The objective of this work is to provide a comprehensive understanding, including parameters, microstructure and properties, of the cold arc cladding process of aluminum coatings on AZ61 magnesium alloy. Three kinds of cladding wires, Al-Mn alloy (AlMn1), Al-Si alloy (AlSi5) and Al-Mg alloy (AlMg5), were cladded on the surface of AZ61 magnesium alloy by pulsed direct current (P-DC) cold arc for a comparative study. The study revealed a correlated relation between the clad geometry and the heat input during the deposition process. The microstructure and composition of the coatings were carefully studied by SEM, EDS and XRD. The properties of the coatings were studied by the micro-hardness, wear resistance and electrochemical corrosion test. The Al-Mn alloy coating has the highest hardness, which is three times that of the AZ61 magnesium matrix. The Al-Si alloy coating has the lowest wear rate, which is about 13.9% of the Mg matrix. The corrosion performance of the Al-Mg alloy coatings is significantly improved byα-Al phase compared to the Mg matrix.

Improvement in the microstructure and mechanical properties of Al-Mn alloy with Zr addition

The effects of content of Zr on the microstructure and mechanical properties of Al-Mn alloy were studied. The results showed that the grain size decreases with the increase of Zr content. With the addition of Zr, the number of primary particles increases, and the content of Mn in solid solution decreases. Tensile testing results show that with the increase of Zr content, the tensile strength and yield strength increased in Al-Mn alloy. The elongation of the recrystallized alloys does not change significantly with the Zr content.

Brown band characteristics of aluminum cladding alloys

Clad materials are a variant of the typical composites, which consist of two or more materials joined on their interface surfaces. Clad materials as metallic composite materials are developed for the needs of user because the single metal often cannot satisfy it application conditions. That is, the advantage of clad materials is that the combination of different properties of materials can satisfy both the need of good mechanical properties and the demand of users such as industrial consumer. The purpose of this study is to study structural aspects in aluminium 3003 clad material with 4343 alloy, after different cladding time. Generally, Al 3003 material is Al–Mn alloy which has superior ductility, but the strength and hardness are low. Aluminium series 4xxx material is Al–Si alloy with high strength and hardness, but low ductility. In our paper we determine the grain sizes of the coated aluminium alloys, before and after cladding, and also the corrosion potentials of these aluminium cladding alloys.

Evolution of Intrinsic Magnetic Properties in L1 0 Mn−Al Alloys Doped with Substitutional Atoms and Correlated Mechanism: Experimental and Theoretical Studies

Mn-Al alloys are promising candidates to fill the performance gap between rare-earth permanent magnets and ferrites, but improving the intrinsic magnetic properties of Mn-Al alloys in the ordered $L{1}_{0}$ phase is not easy. Doping seems to be essential. This work investigates the influence of substitutional atoms on the alloy's intrinsic magnetic properties. The occupation rules for substituents with different valence-electron structures are analyzed, and a strategy to boost the alloy's magnetic properties is developed. This insight should help to promote the engineering of devices that do not rely on rare-earth-bearing magnets, which is of keen interest.

On the compositional partitioning during phase transformation in a binary ferromagnetic MnAl alloy

We introduce a new perspective on the classical massive mode of solid-state phase transformation enabled by the correlative use of atomic-scale electron microscopy and atom probe tomography. This is demonstrated in a binary MnAl alloy which has Heusler-like characteristics. In this system, the τ phase formed by a massive transformation from the high-temperature ε phase is metastable and ferromagnetic. The transformation results in a high density of micro-twins inside the newly grown τ phase. Atomic-scale compositional analysis across the interface boundaries and atomic structure of the micro-twins reveals the involvement of both structural modification and also the compositional partitioning during the growth of the τ phase. This is assisted by the migrating τ/ε interface boundary during transformation. Finally, the role of micro-twins on nucleating the equilibrium phases and the influence of the defects and phase formation on the magnetic properties are discussed.

Microstructural evolution of twin-roll-cast Al–Mn alloy during cold rolling and subsequent annealing: Effect of number of cold-rolling passes

Variations in the shape and microstructure of a 3003 Al alloy strip fabricated by twin-roll casting during cold rolling and subsequent annealing are investigated as a function of the number of cold-rolling passes under the same total rolling reduction. With an increase in the number of cold-rolling passes, the length and width of the cold-rolled sheet increases and decreases, respectively, owing to a reduction in the ratio of the deformation zone length to the mean deformation-zone thickness. A homogenized twin-roll-cast strip has much coarser grains and more particles in the surface region than in the center region. The shape, amount, and distribution of the particles remain unchanged after cold rolling and subsequent annealing, and they are independent of the number of cold-rolling passes. However, as the number of cold-rolling passes increases, the amount of plastic deformation accumulated in the surface region of the cold-rolled sheet increases. As a result, the size of recrystallized grains in the surface region of the subsequently annealed sheet gradually decreases with increasing number of cold-rolling passes owing to the enhanced recrystallization behavior. Therefore, the grain size difference between the surface region and the center region of the annealed sheet reduces significantly, and the homogeneity of the microstructure in the thickness direction of the sheet improves with an increase in the number of cold-rolling passes.

Investigation on fluidity, anodizing and tensile properties of Al–Mn alloys for application in thin-wall cast components

The molten eutectic Al–Mn alloy, whose eutectic point is about 2.0 wt%, possesses sound fluidity that might satisfy the demands of the thin-wall parts of 3 C products and the auto industry. In this research, the anodic oxide film, fluidity of the melts and tensile property of Al–Mn alloys with additional manganese amounts ranging from 0.6 wt% to 2.7 wt% were studied. The x-ray diffraction test was carried out for the identification of the phases in the fabricated Al–Mn alloys. The commercial ADC12 alloy was selected for comparison of performance. The identical anodic oxidation process and the coloring process were implemented on both the commercial ADC12 alloy and Al–Mn alloys, and the effects on their micro- and macro-structures were observed. According to the results of the spiral fluidity tests, the fluidity length of the molten Al-2.0Mn alloys was close to that of the commercial ADC12 alloy. And the optimal ultimate tensile strength of the Al–Mn alloys was obtained at a manganese content of 2.0 wt%. In addition, analysis on the benchmarks of color difference, film thickness and roughness showed that the appearance quality of anodic oxide film of the Al–Mn alloys was superior to that of the commercial ADC12 alloy. Moreover, as for the Al–Mn alloys, the benchmarks of color difference and roughness of these anodic oxide films were raised with the increase of manganese contents.

Realization of large coercivity in MnAl permanent-magnet alloys by introducing nanoprecipitates

Abstract Acquisition of large coercivity remains as a key issue in MnAl permanent-magnet alloys. In this work, we successfully introduce rhombohedral nanoprecipitates with the size of ∼20 nm into L10 MnAl alloys via doping 0.2 at.% Tb and melt spinning technology. The motion of magnetic domain walls can be more effectively pinned by the dispersive nanoprecipitates. This results in an improved coercivity of 5.43 kOe in Tb-0.2 at.% powders which is 22% larger than that of the binary powder without significant degrading in saturation magnetization and magnetocrystalline anisotropy. This work may provide a new method to improve the coercivity in MnAl permanent magnets.

Metamagnetic behavior in L10-MnAl synthesized by the post annealing of electrodeposited MnAl powder

The effect of annealing temperature on MnAl alloy powder synthesized by electrodeposition method was investigated. Single L10-MnAl (τ-phase) with nearly stoichiometric composition was obtained by electrodeposition method. In annealed at 400°C sample coercivity of 12.3 kOe was observed. And by annealing at 450–550°C, metamagnetic behavior was observed. In these samples, the main phase was τ-phase although weak peaks of low-temperature Al-rich γ2 phase appeared. The order parameter S of the τ-phase exhibited a peak value with variation of the annealing temperature. The peak value was 0.90 at an annealing temperature of 500°C, where the metamagnetic behavior was most clearly observed. This indicates that the nearly perfectly ordered τ-phase shows metamagnetism and the Mn atoms occupying the Al sites play an important role in the metamagnetism of the τ-phase.

Strain-induced phase transformation of an Mn-Al alloy during hot compression

The high-temperature deformation of an Mn-Al alloy with a chemical composition of Mn51Al47C2 was assessed using hot compression testing at the temperature range of 600–800 °C and the strain rates ranging 0.001 s−1 to 1 s−1. Optical microscopy (OM), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD) and X-ray diffraction (XRD) analyses were implemented to characterize the samples. It was found that during deformation, the τ phase dynamically transformed into γ2+ β + ε phases and the transformation temperature reduced from the equilibrium value of about 790 °C down to < 750 °C. In such temperature range, considering the lower strength of the produced phases, the dynamic strain-induced phase transformations caused a flow softening in the stress-strain curves. However, deformation at temperatures lower than 700 °C, in the state of τ phase stability, led to dynamic recrystallization which was responsible for flow softening. The standard approach was applied to calculate the processing maps which represented an optimal working region in the temperature range of 650 °C up to 700 °C with the strain rates lower than 0.1 s−1 in order to avoid flow localization and dynamic phase transformations.

Irradiation induced enhancement of ferromagnetic τ-phase in MnAl alloy thin films on Si substrate

Ferromagnetic L10 MnAl phase was achieved in as-grown MnAl alloy thin films by using 250 keV H+ ion irradiation without conventional post annealing. The magnetic properties and crystallinity of MnAl thin film got modified with increase in irradiation fluence. The magnetic coercivity was found to be maximum (2500 Oe) at the fluence of 5 × 1014 ions cm−2. The hysteresis curve for the sample irradiated by H+ ions with fluence of 5 × 1016 ions cm−2 exhibited highest saturation magnetization (130 emu/cc) among all irradiated films. The increase in irradiation fluence led to larger grain growth as confirmed from AFM results. The magnetic domain pattern observed by MFM images confirmed the presence of ferromagnetic τ-phase in irradiated samples. The present study establishes that the H+ ion-irradiation can be an effective technique to tailor the structural as well as magnetic properties of MnAl thin films.

Dendrite growth behavior in directionally solidified Fe–C–Mn–Al alloys

In this study, a series of directional solidification experiments were conducted to investigate the dendritic growth behavior in Fe–C–Mn–Al alloys with varying C contents (0.06, 0.24 and 0.68 wt%). Because of the large compositional undercooling at the front of the solid–liquid interface, dendrites developed at various growth velocities. Under the experimental conditions in the present study, the relationships between the primary dendrite arm spacing (PDAS) and growth velocity for the 0.06C, 0.24C and 0.68C alloys were λ0.06C = 11.75·V−0.30, λ0.24C = 10.38·V−0.32, and λ0.68C = 10.56·V−0.31 respectively. Comparison of the experimental data with prediction models confirmed that the PDAS of the Fe–0.68C–18.02Mn–1.35Al alloy can be predicted using the Kurz-Fisher model. The length of the mushy zone increased, and the high-temperature solidification mode changed with increasing C content, leading to complex changes in the PDAS. The results indicate that the solidification structure of Fe–C–Mn–Al alloys can be refined by increasing the growth velocity and that modifying the C content can be beneficial in avoiding the peritectic reaction.