Al-Mn Alloys Research Articles

Влияние повторных мартенситных превращений на свойства сплава с памятью формы Cu—Al—Mn

Влияние повторных мартенситных превращений на свойства сплава с памятью формы Cu—Al—Mn

Особенности гистерезиса мартенситного превращения в сплавах Cu—Al—Mn

Особенности гистерезиса мартенситного превращения в сплавах Cu—Al—Mn

Insights into formation and stability of τ-MnAlZx (Z = C and B)

The τ-phase MnAl alloys are promising candidate for rare earth free permanent magnets. In this study, In order to better understand the MnAl ε→τ phase transition mechanism in a continuous cooling process and metastable MnAl τ-phase high temperature stability, Mn0.54Al0.46, Mn0.55Al0.45C0.02 and Mn0.55Al0.45B0.02 alloys were systematically studied by in situ synchrotron X-ray powder diffraction (SR-XRD). The relationship between τ-phase formation tendency and different cooling rates of Mn0.55Al0.45C0.02 was investigated. Besides, the high temperature stabilities of undoped τ-MnAl and carbon/boron doped τ-MnAl were studied. Differential thermal analysis (DTA) was also employed to study the phase transformation as well. The research results show that a high cooling rate of 600 °C/min leads to a 50/50 wt% mixture of ε- and τ-phase; almost pure τ-phase was obtained when cooled at a moderate cooling rate of 10 °C/min; while for a slow cooling rate of 2 °C/min, the τ-phase partially decomposed into β and γ2 phases. No intermediate ε’-phase was observed during the ε→τ phase transition during the experiments. For the boron and carbon doped τ-MnAl, the 800 °C high temperature stability experiments reveal that C stabilizes the τ-MnAl while doped B destabilises the tetragonal structure and it decomposes into β- and γ2-phases.

Zinc Diffusion Coatings on Aluminium for Improved Pitting Resistance

The automotive industry has replaced copper tube based heat exchangers with all-aluminium solutions during the past years in order to reduce weight, material costs and environmental impact. Conversely, the use of aluminium tubing in the HVAC&R (Heat, Ventilation, Air Conditioning and Refrigeration) heat exchanger market is limited due to the much more demanding lifetime requirements. One way of obtaining the required level of safety against failure of aluminium tubing in such applications is corrosion protection by surface modification. This work investigates the effect of surface alloying with zinc on the pitting resistance of heat exchanger tubes. Pure zinc was applied on flat, thin-walled (≈ 400 µm) multi-port extruded Al-Mn alloy tubes by thermal arc spraying immediately after extrusion, resulting in a sub-micron thick metallic Zn layer on the surface. The tubes were subsequently heat treated to obtain various Zn-rich diffusion layers ranging up to about 70 µm into the alloy substrate. Zn depth profiles were determined by glow discharge optical emission spectroscopy (GD-OES). Corrosion testing was performed by exposure to a cyclic acidified (pH 3) synthetic seawater fog test (ASTM G85 annex A3), normally referred to as the SWAAT test. Open circuit potentials were measured on separate samples as a function of time during immersion in the SWAAT solution at 25 °C. The extent of corrosion as a function of time was determined by weight loss on samples retrieved from the salt spray cabinet at predetermined time intervals for a period of up to eight weeks. The maximum pit depth on each sample was measured by use of a light microscope with a micrometre focusing dial. Ten replicate samples (each 25 mm x 100 mm in size) for each substrate/coating combination were tested, allowing analysis of the maximum pit depth data from extreme value probability plots. The open circuit potential of the Zn diffusion coated samples in artificial seawater solution was about -0.95 V (SCE), shifting only 10 mV in positive direction during 24 h of immersion. The corrosion potential of the Al-Mn alloy substrate remained constant at -0.74 V (SCE) under similar conditions. The cathodic protection provided by the Zn-rich diffusion layers effectively protected the Al-Mn alloy tubes against formation of deep pits during SWAAT testing. No pits deeper than about 50 µm had formed on the Zn diffusion coated samples after eight weeks of exposure, whereas pit depths exceeding 200 µm was observed on uncoated reference samples already after two weeks. However, weight loss measurements showed that the (uniform) corrosion rate of the anodic Zn-rich diffusion layer was nearly two orders of magnitude higher than that of the Al-Mn alloy substrate under the aggressive low pH conditions prevailing during SWAAT exposure. The results suggest that a lower Zn load than that realizable by thermal arc spraying is required to obtain optimal Zn diffusion profiles in terms of service life of the heat exchanger tubing.

Evaluation of Al and Al Alloy Films Formed By Electrochemical Method

A zinc plated to prevent corrosion, however, a zinc will be exhausted within twenty years1) 2). An aluminum is one of the most promising candidates as alternative material. An aluminum is the third clarke number material and it is very rich. An aluminum has a great ionic tendency, but it forms very stable oxide film and it suitable as corrosion-resistant materials. However deposition potential of aluminum is less noble than hydrogen evaluation potential. Therefore, an aluminum is difficult to be plated from aqueous solution. An organic solvent and ionic liquid are used as a solvent for Al plating. A dimethyl sulfone (DMSO2) shows low volatility, high stability and wide potential window. Therefore this study used DMSO2as a solvent for Al and Al alloy plating. But the dimethyl sulfone has high viscosity, the plating films are influenced by agitation. We discuss the influence of metallic salts and organic additives on the crystallographic orientation of the films. Electrochemical experiments were carried out in three-electrode cell using a potentiostat (Hokuto Denko HZ-5000) between 110 oC and 150 oC. The reference electrode was an Al/Al3+ electrode (-1.676 V vs. SHE). The counter electrode was an aluminum plate. The working electrodes were 99.99 % pure copper plate. The plating solution was composed of AlCl3 and DMSO2. The ratio between DMSO2 and AlCl3 is 10:3, AlCl3 concentration is 23 mol% and 10:5, AlCl3 mol concentration is 33 mol%. Dehydration was carried out under a nitrogen atmosphere at 150 oC for 30 minutes. As analysis method of the samples, we used X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS). Figure 1 shows SEM micrographs of Al-Mn alloy films plated from baths whose AlCl3mol concentration was 23 mol% (a,b,c) or 33 mol% (d,e,f,g,h,i,j) by changing deposition potential. The deposition potential region of film formation was different by Al ion concentration. The films were plated at deposition potential region between -1.5 and -3.0 V for 23 mol% Al ion concentration bath and that between -3.0 and -4.0 V for 33 mol% Al ion concentration bath. When the aluminum ion concentration was 23 mol%, grain size was increased by changing deposition potential from -1.5 V to -4.0 V and surface roughness also increased. The manganese content was increased with increasing deposition potential and the maximum Mn content, 26.5 at% at -2.0 V deposition potential. Then the manganese decreased with increasing deposition potential. When the aluminum ion concentration was 33 mol%, surface morphology was changed by chansing deposition potential from -1.5 V to -4.0 V. A clear dependence between deposition potential and surface morphology was not observed. Moreover no clear relationship between deposition potential and Mn content was not also observed. The maximum Mn content, 10.9 at%, was obtained at deposition potential of -3.5 V. The films plated from 23% Al ion concentration bath showed much higher Mn content than those plated from 33% Al ion concentration bath. Ammonium chloride (NH4Cl) is added to the bath in order to decrease the viscosity of the bath as additive. The melting point of the plating solution composed of AlCl3 and DMSO2 was decreased by adding NH4Cl. According to decreasing melting point, the viscosity seems to decrease. The surface morphology of the films is drastically affected by adding of small amount of NH4Cl. By adding of NH4Cl, there is not influenced by stirring, but the particle size is increased. Pinholes occurred increasing additive amount. When ammonium chloride added to the solution, the intensity of the Al(200) peak is decreased. The plating films have no metallic luster. It is found that the surface morphology of the plating films were changed accompanied by metallic salts and additives. The maximum Mn content, 26.5 at% at -2.0 V deposition potential. The films adding NH4Cl is not influenced by stirring, but the crystalline size increased. Acknowledgements This work was partially aided by the MEXT-supported Program for the Strategic Research Foundation at Private Universities. Reference 1) T.Adaniya, J. MMIJ, 128, 57-64 (2012) [in Japanese]. 2) K. Halada, M. Shimada and K. Ijima. J. Japan Inst. Metals, 71, 831-839 (2007) [in Japanese]. Figure 1

Corrosion Resistance of Zinc-Rich Metallic Coatings on Aluminum

Thin walled aluminum heat exchanger tubes, with solid-solution Zn-rich surface are widely used by the automotive industry and considered by the HVAC&R (Heat, Ventilation, Air Conditioning and Refrigeration) market for improved corrosion resistance against pitting. It is well known that alloying Al with Zn causes decrease in the corrosion potential in chloride solution.1 Thus, Zn-rich coating can provide cathodic protection to the aluminum substrate, in particular prevent pitting corrosion. However, corrosion rate of Zn itself is quite high in chloride solution.2 This work investigates the extent to which the self-corrosion of the Zn-rich layer can be a limiting factor in determining the service life time of the heat exchanger tubes. Zinc was applied on AlMn alloy extruded tubes by thermal arc spraying immediately after extrusion. Typical Zn load on the surface was 0.8 ± 0.2 mg/cm2. The tubes were subsequently subjected to heat treatment at various temperatures (350 - 430°C) and durations to obtain solid-state AlZn alloy diffusion layer with varying thickness and Zn-concentration profiles at the surface of the AlMn substrate. The Zn depth profiles were characterized by glow discharge optical emission spectroscopy (GD-OES). Corrosion rate was determined by weight loss resulting from immersion for predetermined times in acidified artificial sea water solution of pH 3 at 25°C for slight acceleration of the corrosion rate, during which the open circuit potential change was recorded with respect to time. The morphology and composition of the Zn-rich layer before and after corrosion were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).The Zn concentration distribution in the layer could be modeled by the solution to Fick's 2nd law with appropriate boundary conditions, giving an effective diffusion coefficient for Zn in the Al substrate of order 10-10 cm2/s in the temperature range of interest, varying according to the Arrhenius law with respect to temperature. Zn-rich layer thickness obtained on the samples heat treated at selected conditions varied approximately in the range 35 to 80 µm with increasing heat treatment temperature and time, corresponding to Zn surface concentrations of 28 to 7 wt%, respectively. Reduction in thickness due to corrosion, calculated from the weight loss measurements by taking into consideration the density depth-profile of Zn, which was obtained from the GD-OES data, increased with increasing thickness of the Zn-rich layer. Unexpectedly, decreasing Zn concentration level in the layer did not have a significant effect on the corrosion rate, unless it was lower than a threshold of a few wt%, which appeared to be sufficient to give the necessary protection. The results confirmed also that Zn gave satisfactory protection against pitting corrosion. Corrosion potential of samples as coated with Zn (no heat treatment) reached the pitting potential of the AlMn substrate in about 4 days. After 11 days of immersion, corrosion potential of the samples heat treated at 350°C for 2 hours increased up to about 30 mV below the pitting potential of the substrate, while the corrosion potential of the samples heat treated at 430°C for 4 hours remained about 120 mV lower than the pitting potential of the substrate. The reduction in thickness after 11 days of immersion for those heat treatment conditions was 23 µm and 54 µm, respectively. These results indicate that optimal Zn concentration and Zn-rich layer thickness, in terms of service life and loss of thickness, lie at levels much lower than those used in this study. The optimal concentration needs to maintain the corrosion potential at a level lower than the critical pitting potential. At the same time, the Zn concentration level in the layer has to be low enough to restrict the rate of self-corrosion, such that the layer thickness can also be reduced to give sufficiently long service life time. The well-known relationship between the corrosion potential of AlZn alloys and Zn concentration1 was extended over a wide concentration range and related further to the corrosion rate in acidified synthetic seawater. The database thus developed is useful for optimizing the Zn-rich layer thickness and Zn concentration profile in the layer to minimize uniform corrosion, and therefore maximize service lifetime, without reducing the protection against pitting.

Spectro-photometric determinations of Mn, Fe and Cu in aluminum master alloys

Highly reliable, fast and cost effective Spectro-photometric methods have been developed for the determination of Mn, Fe & Cu in aluminum master alloys, based on the development of calibration curves being prepared via laboratory standards. The calibration curves are designed so as to induce maximum sensitivity and minimum instrumental error (Mn 1mg/100ml-2mg/100ml, Fe 0.01mg/100ml-0.2mg/100ml and Cu 2mg/100ml-10mg/ 100ml). The developed Spectro-photometric methods produce accurate results while analyzing Mn, Fe and Cu in certified reference materials. Particularly, these methods are suitable for all types of Al-Mn, Al-Fe and Al-Cu master alloys (5%, 10%, 50% etc. master alloys).Moreover, the sampling practices suggested herein include a reasonable amount of analytical sample, which truly represent the whole lot of a particular master alloy. Successive dilution technique was utilized to meet the calibration curve range. Furthermore, the workout methods were also found suitable for the analysis of said elements in ordinary aluminum alloys. However, it was observed that Cush owed a considerable interference with Fe, the later one may not be accurately measured in the presence of Cu greater than 0.01 %.

Microwave Absorbing Properties of MnAlFe Magnetic Powder

MnAlFe alloy was prepared by the combined use of smelting, high-energy ball milling and tempering heat treatment process. The phase composition and microwave absorbing properties of MnAlFe alloy were investigated by X-ray diffractometer(XRD) and vector network analyzer. The results show that the powders consist of Al8Mn5 single phase with different Fe content; the dielectric loss and the magnetic loss increases with the addition of Fe, the resonant frequency and absorption peak of ε″ and μ″ moves towardslower frequency region simultaneously. The (Al8Mn5)99Fe exhibits preferably comprehensive microwave absorbing properties in the range of 6-18 GHz. The value of the minimum reflectivity and absorption peak frequency with the coating thickness of 1.5 mm, are -23.1 dB, 15.04 GHz respectively. Owing to the wide applications of electromagnetic waves in the range of 1–4 GHz for mobile phone, local area network, radar systems and so on over the past few decades, the serious problems of the electromagnetic interference and electromagnetic compatibility have become increasingly prominent in recent years. Microwave absorbing materials, which possess special performance for absorbing electromagnetic wave, have been applied in both civil and military fields and play an important role in camouflage technology. In military field, stealth technology to reduce and eliminate the electromagnetic radiation and electromagnetic interference resulting from the broad applications of various kinds of electronic and microwave instruments, stealth technology plays an important strategic role in the wars in future[1-2]. The microwave absorbing materials can be used to reduce radar cross section for military use. For this reason, the microwave absorbing material is vitally important for both civil and military fields[3-7]. In view of this utilization, excellent microwave absorbing materials should exhibit strong microwave absorption properties over a wide frequency range and need to be thin and light in weight. It has an important meaning to the application of magnetic microwave absorbing materials. MnAl alloy can be used as microwave absorbent. It has properties such as light in weight, good thermal stability and corrosion resistance[8-11]. But as permanent magnets, MnAl has shortcomings such as their difficulties of fabrication and high costs that prevent them from being used as permanent magnets. A great value would be brought to either theory or practice through proper treatments as further improvement in properties. In this paper, we will discuss the effects of changing relative content of Fe on absorption properties of Al8Mn5 alloy.

Ternary phases forming adjacent to Al3Mn[sbnd]Al4Mn in Al[sbnd]Mn[sbnd]TM (TM = Fe, Co, Ni, Cu, Zn, Pd)

The AlMn alloy system contains complex intermetallics in its Al-rich part, and this was the first system where quasiperiodic structures were recognized. In the present work, the solubility of TMs (TM = Fe, Co, Ni, Cu, Zn and Pd) in the stable binaries, the stabilization effect of these elements on the metastable binaries and the formation of ternary compounds are specified and compared. While the solubility of all these TMs in hexagonal μ-Al4Mn and λ-Al4Mn is low, the high-temperature orthorhombic T-Al3Mn dissolves up to at least 14.5, 12, 16 and 7.5 at.% Fe, Cu, Zn and Pd, respectively. The metastable hexagonal φ-Al10Mn3 is stabilized by Fe, Co and Ni in wide ternary compositional regions, and in AlCoMn such a region propagates up to Al5Co2. In alloys with Fe, Co and Ni, a ternary hexagonal phase isostructural to the AlCrNi ζ-phase (P63/m, a ≈ 1.76, c ≈ 1.25 nm) is formed along ∼80 at.% Al, while in alloys with Cu and Pd the orthorhombic so-called R-phase (Bbmm, a ≈ 2.41, b ≈ 1.25, c ≈ 0.76 nm) was found at similar compositions. This structure is also known in AlZnMn but at much lower-Al Al68Zn14.5Mn17.5, while in the range of 75–80 at.% Al a monoclinic phase isostructural to η-Al11Cr2 (C2/c, a ≈ 1.76, b ≈ 3.04, c ≈ 1.76 nm, β ≈ 90°) is formed. In addition to the stable decagonal D3-phase in AlFeMn and AlPdMn reported earlier, the stabilization of binary AlMn D3-phase was revealed around Al64Cu20Mn16.

Low-energy mechanically milled τ-phase MnAl alloys with high coercivity and magnetization

The high cost of rare earth elements makes the use of high-performance permanent magnets commercially very expensive. MnAl magnetic material is one of the most promising Rare-Earth-free permanent magnets due to its obvious characteristics. However, the coercivity of MnAl alloys produced by melt spinning followed by appropriate treatment is relatively low. In this investigation, a high coercivity up to 5.3 kOe and saturation magnetization of ∼62 emu/g (with an applied magnetic field of 19.5 kOe) were obtained in the mechanically milled τ-phase Mn57Al43 alloy. As milling time goes on, the coercivity firstly increases and then decreases, leading to the formation of knee-point coercivity, while the saturation magnetization decreases simultaneously. The structural imperfections such as disordering and defects play the most important role in the changes of magnetic properties of τ-phase MnAl alloys processed by low-energy mechanical milling. The present results will be helpful for the development of processing protocols for the optimization of τ-phase MnAl alloys as high performance Rare-Earth-free permanent magnets.

AlMn Transition Edge Sensors for Advanced ACTPol

Advanced ACTPol (AdvACT) will use an array of multichroic polarization-sensitive AlMn transition edge sensor (TES) bolometers read out through time-division multiplexing. Aluminum doped with a low concentration of manganese can be deposited to a bulk film thickness for a more reliable superconducting critical temperature uniformity compared to thin bilayers. To build the TES, the AlMn alloy is deposited, over Nb wiring, to a specific thickness to set the TES normal resistance. The doping concentration of manganese coarsely defines the TES critical temperature, while a fine tuning is achieved by heating the deposited film to a specific temperature. The TES island is connected to the thermal bath via four silicon-nitride membranes, where their geometry defines the thermal conductance to the temperature of the bath. Lastly, the TES heat capacity is increased by addition of PdAu electrically connected to the AlMn film. Designs and performance characteristics of these AlMn TESs are presented for use in AdvACT.

Tensile properties, residual stress distribution and grain arrangement as a function of sheet thickness of Mg–Al–Mn alloy subjected to two-sided and simultaneous LSP impacts

Two-sided and simultaneous laser shock peening impacts is considered as a novel surface treatment technology for the turbine blade and thin-walled component. In this paper, tensile properties of Mg–Al–Mn alloy specimens with different sheet thickness under two kinds of laser shock peening strategies were investigated, and an overlapping three-dimension axisymmetric numerical model was developed to analyze the effects of sheet thickness on residual stress distributions. Meanwhile, special attentions were paid to the in-depth microstructural evolution as a function of sheet thickness. Results showed that sheet thickness had an important influence on the tensile properties of Mg–Al–Mn alloy, and the generated residual stress distribution and grain arrangement were two important factors. The corresponding influence mechanism of sheet thickness on the tensile properties of Mg–Al–Mn alloy was also presented, and the optimal thickness of Mg–Al–Mn alloy sheet may be 4mm or more.

Effect of Ca addition on the corrosion behavior of Mg–Al–Mn alloy

The microstructures and corrosion resistance of magnesium–5wt% aluminum–0.3wt% manganese alloys (Mg–Al–Mn) with different Ca additions (0.2–4wt%) were investigated. Results showed that with increasing Ca addition, the grain of the alloys became more refined, whereas the corrosion resistant ability of the alloys initially increased and then decreased. The alloy with 2wt% Ca addition exhibited the best corrosion resistance, attributed to the effect of the oxide film and (Mg,Al)2Ca phases which were discontinuously distributed on the grain boundaries. These phases acted as micro-victims, they preferentially corroded to protect the α-Mg matrix. The oxide film formed on the alloy surface can hinder the solution further to protect the α-Mg matrix.

Structure and Properties Studies of Rapidly Solidified Al-Mn Alloys

Rapid solidification (RS) combined with plastic consolidation by hot extrusion was used to produce Al alloys with additions of varied concentration of Mn. RS flakes were manufactured using an inert gas atomizing of the molten alloy and the spray deposition on the water-cooled cooper roll. Rods of 7mm in diameter were received using cold pressing of RS-flakes, vacuum degassing and hot extrusion procedures. Mechanical properties of as extruded materials were tested in hot compression at temperature range 293K - 773K. It was found that the flow stress was reduced monotonically with deformation temperature for all tested materials. RS alloys exhibit higher mechanical properties than those produced by conventional metallurgy methods. Higher mechanical properties of RS materials are ascribed to beneficial particles morphology obtained due to the rapid solidification. Development of fine Al6Mn particles was observed in all tested RS-materials.

3D Morphology and Formation Process of the Icosahedral Quasicrystalline Phase in Rapidly Solidified Al–Mn Alloy

Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun Al–18Mn alloy (in wt%). Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons. 3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching. A model has been proposed to describe the formation process of the icosahedral phase and α-Al during the rapid solidification. The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles, and subsequently engulfed by the α-Al which propagates in a planar morphology.

Effect of Varying Al/Mn Ratio on Phase Transformation in Cu–Al–Mn Shape Memory Alloys

In the present study, an attempt has been made to study the effect of the proportion of the main alloying constituents in a Cu–Al–Mn alloy, which is a known shape memory material. Four compositions of the alloy with varying ratios of Al:Mn, varying from 1 to 4 [added to copper], were synthesized using the liquid metallurgy route. After appropriate heat treatment to induce shape memory behaviour, they were studied for microstructure, X-ray diffraction, hardness and transformation temperature in an attempt to understand the effect of the varying ratios of the major alloying constituents on the properties mentioned. With an increase in the Al:Mn ratio, increase in grain size as well as cast hardness were observed. On the other hand, an increase in percentage decrease in hardness was observed with increase in Al:Mn ratio. Increase in Al:Mn ratio also favoured formation of martensitic structure with less amount of retained austenite.

The characterization of near‐surface defects evolved on aluminum–manganese alloys during hot rolling

Hot rolling laboratory experiments were performed on an Al–Mn alloy, utilizing a rolling tribo‐simulator to characterize the evolution of near‐surface defects induced by tribological interactions between the work roll and alloy surfaces. A ten pass hot rolling schedule was conducted on Al–Mn samples using an AISI 52100 work roll polished to a surface roughness (Ra) of 0.01 μm. Micro‐cracks formed on the alloy surfaces at the first pass were observed to initiate at grain boundaries and propagate less than 1.5 μm deep into the subsurface region. The faces of the micro‐cracks in the subsurface region were observed to be covered with MgO. The surface of the samples were observed to possess a top 90‐nm‐thick oxide‐rich layer, which was mostly composed of MgO. MgAl2O4 and Al2O3 were also observed on the alloy surface at this stage of rolling. After ten passes, near‐surface features on the Al–Mn alloy samples included MgO‐rich islands and transverse cracks. Cracks extended more than 2 μm deep into the subsurface. Crack faces were covered with surface deformation induced crevices as well as MgO. The near‐surface was also composed of nano‐crack induced damaged areas, filled with porous nanocrystalline oxides. These damaged areas extended 0.5 μm into the subsurface region beneath a 60‐nm‐thick MgO film. The nanocrystalline oxide layers possessed embedded aluminum nano‐particles. The microstructure of the near‐surface layer suggests that magnesium diffusion to the free surfaces and crack formation play an important role in its evolution. Copyright © 2015 John Wiley & Sons, Ltd.

Experimental modelling of critical damage obtained in Al–Mg and Al–Mn alloys for both annealed state and previously deformed by ECAP

Assessing the damage produced in plastic deformation processes permits the optimum manner to shape a material that could avoid any cracks from appearing. In this present research work, the absolute critical damage in the following aluminium alloys: AA5754, AA5083 and AA3103 is to be determined. In order to do this, compression tests between plane-shape dies will be performed for the abovementioned alloys at a temperature range which varies from 25°C to 300°C and using Cockroft–Latham's prediction model. Furthermore, the results obtained by finite volume simulations will be compared with those obtained by experimental tests with isothermal upsetting. Given that in these last few years there has been a growing interest in obtaining mechanical components from submicrometric and/or nanometric structure materials which have been previously-processed by severe plastic deformation (SPD), this present research work deals with the determination of absolute critical damage for the abovementioned alloys once they have been ECAP (Equal Channel Angular Pressing) processed. This is considered to be of interest since it could allow the prediction of optimal processing conditions in advance.

Spin-state dependence of electrical resistivity and thermoelectric power of molten Al–Mn alloys: Experiment and theory

We present experimental measurements of resistivity and thermoelectric power of liquid alloys, Al1−x–Mnx, (x = 0.12, 0.14, 0.16, 0.18, 0.20). The resistivity increases from 28.88 μΩ cm for pure aluminum to 123.3 μΩ cm for the alloy. No resistivity extremum is observed near the Mn concentration x = 0.14, in contrast to that observed in the quasi-crystalline state. At 1323 K. The temperature coefficient of the experimental resistivity is found to have a minimum value in the near vicinity of x = 0.16. For all these five compositions the thermoelectric power is negative and does not display any anomaly. Also we have proposed theoretical model, based on Faber Ziman formalism, to calculate both resistivity and the thermoelectric power.The neutron scattering experiment on Al0.80Mn0.20 liquid alloy confirmed that the effective spin of Manganese atoms had a mean value around 1 and that the Manganese could exist in two states of different magnetic moments. By minimizing the energy of the spin flip, we demonstrated the fact that Manganese appears in Al1−xMnx alloys as a mixture of Manganese atoms of spin 1/2 and 3/2 in proportions equal to 7/12 and 5/12, respectively. The Manganese atoms with one spin value different of zero may be considered as a binary alloy (B. Grosdidier, A. Ben Abdellah, K. Bouziane, S. M. Mujibur Rahman and J. G. Gasser, Phil. Mag. 93 no 26 (2013) p.3576.) owing to the spin dependence of the exchange and correlation. In this work, we treated Manganese with its two spin values as a quaternary alloy. Consequently, in our calculations, we treated Al–Mn as five component alloys. This allowing us to extend the Faber Ziman formalism originally designed for a binary alloy to a five-component formalism. Our theoretical results are in fairly good agreement with our experimental values which validates the assumptions of our model.

Synthesis and Magnetic Properties of τ-MnAlC Powders.

In order to improve the hard magnetic properties of MnAl alloy, it is critical to fabricate fine τ phase MnAl powders. In addition, a rapid cooling process and an addition of stabilization elements are required to fabricate a homogeneous phase because a τ phase is a metastable structure. In this study, τ-Mn54Al(46-x)C(x) (x = 0, 1, 2) powders were prepared by melt-spinning and subsequent annealing and milling processes. As a result, a main phase was revealed as a high temperature e phase in melt spun MnAI ribbons. And a subsequent annealing in the temperature range of 450-650 degrees C resulted in the formation of a τ phase. A maximum saturation magnetization (M(s)) value of 96.56 emu/g was obtained when the melt-spun τ-Mn54Al44C2 ribbons were annealed at 500 degrees C for 10 min. However, a milling process increased the coercivity up to 3804 Oe but simultaneously reduced M(s) down to 60.34 emu/g.