Al Ca Alloy Research Articles

Effect of dynamic precipitation and twinning on dynamic recrystallization of micro-alloyed Mg–Al–Ca alloys

Two micro-alloyed Mg–Al–Ca alloys were designed, using thermodynamic calculations, to form precipitates during hot deformation. Hot compression tests were carried out at temperature range from 300°C to 450°C at strain rates of 0.1s−1, 0.01s−1 and 0.001s−1. Precipitation behavior was analyzed by SEM with BSE and EDS detectors. Dynamic recrystallization and twinning were characterized by optical microscopy. It appears that dynamic precipitation retarded dynamic recrystallization.

Compression-creep response of magnesium alloy DieMag422 containing barium compared with the commercial creep-resistant alloys AE42 and MRI230D

The development of creep-resistant magnesium alloys that avoid the use of rare-earth alloying elements is an important area of research. The creep response of Mg–Al–Ca alloy containing barium (DieMag422) was compared to that of commercially available creep resistant magnesium alloys AE42 and MRI230D. The creep tests were performed between 175°C and 240°C at stresses between 60MPa and 120MPa. From the temperature and stress dependence of the minimum creep rate, the apparent activation energy Qc and the stress exponent n for creep were calculated. The concept of a threshold stress was applied. True stress exponents nt close to 5 were calculated. Microstructural investigations and phase analysis were performed on the as-cast materials as well as after creep. Fine precipitates could be identified that justified application of the concept of threshold stress. The DieMag422 alloy shows an improvement in creep resistance at low stresses compared with the other two alloys AE42 and MRI230D.

Effects of Zn/Sn mass ratio on microstructure and mechanical properties of Mg–Zn–Sn–Al–Ca alloys

The effects of the Zn/Sn mass ratio on microstructure and mechanical properties of the as cast and the as rolled Mg–xZn–ySn–2Al–0·2Ca (x+y = 9 wt-%) alloys have been investigated by optical microscopy, X-ray diffraction, SEM and mechanical testing to explore the feasibility of developing a heat treatable high strength wrought Mg alloy by water cooling copper mould casting under pressure plus plastic forming. The as cast alloys are characteristic of divorced eutectics and are composed of four phases, i.e. α-Mg, Mg32(Al, Zn)49, Mg51Zn20 and Mg2Sn. The alloy with the lower Zn/Sn mass ratio contains a higher amount of the Mg2Sn phase and a lower fraction of the Zn containing phases. The as cast Mg–4·5Zn–4·5Sn–2Al–0·2Ca alloy is characteristic of the finer grain size and the fewer amount of the intermetallic compounds at grain boundaries, showing a fairly good roll forming ability and the optimal combined mechanical properties, with the ultimate tensile strength (UTS), yield tensile strength (YTS) and elongation to rupture (El) of 243 MPa, 170 MPa and 13·9% respectively. Solution treatment can improve the roll forming ability of the Mg–Zn–Sn–Al–Ca alloys to a large extent. The as rolled Mg–4·5Zn–4·5Sn–2Al–0·2Ca alloy exhibits the well balanced mechanical properties among the three alloys. The alloy prepared by direct rolling exhibits UTS, YTS and El of 351 MPa, 245 MPa and 7·1% respectively, while that prepared by solution rolling exhibits UTS, YTS and El of 406 MPa, 285 MPa and 6·6% respectively. Solution rolling has a more obvious strengthening effect on the Mg–Zn–Sn–Al alloys than direct rolling. The as investigated Mg–4·5Zn–4·5Sn–2Al–0·2Ca alloy is a promising candidate for future commercial applications in the Mg–Zn–Sn system.

The Effects of Copper Addition on the compression behavior of Al-Ca Alloy

The Al-Ca-Cu alloys containing varying amount of Cu are used to study the effect of Cu addition on their deformation behavior at varying strain rate (0.001/s, 0.01/s, 0.1/s, 1/s).The material is prepared using stir casting technique The yield stress, flow stress and elastic limit are measured from the true stress-strain graph .The Strain Rate sensitivity and strain hardening exponent are also determined for each material at different strain rate. The Strain Rate Sensitivity of this alloy is very low. These values strongly demonstrate that compressive deformation of Al-Ca-Cu alloys almost independent to the strain rate at room temperature deformation.

Investigating viscosity variations of molten aluminum by calcium addition and stirring

The effect of calcium addition on the viscosity of Al–Ca alloys before, during and after stirring is investigated using a midfield falling ball viscometer. Due to the independency of this method from stirring, the viscosity measurement was done without creating any turbulence on the surface. The viscosity rises by increasing the stirring time which can be intensified by additional calcium content. Following the stirring and during relaxation, viscosity drops steadily until it reaches the viscosity of the melt before stirring. Oxides agglomeration a cluster formation during relaxation is the main factor responsible for the viscosity reduction. In fact Stirring not only accelerates the oxide formation, but also breaks and disperses these oxides to individual fine-size oxide particles.

Effects of cooling rate and pressure on microstructure and mechanical properties of sub-rapidly solidified Mg–Zn–Sn–Al–Ca alloy

Effects of cooling rate and pressure on microstructure and mechanical properties of sub-rapidly solidified Mg–6Zn–3Sn–2Al–0.2Ca alloy were investigated by OM, XRD, SEM and tensile testing. The alloy prepared by steel mould casting with no applied pressure is mainly composed of four phases i.e. α-Mg, Mg2Sn, MgZn and Mg32(Al,Zn)49, while those prepared by water-cooling steel mould casting under pressure and water-cooling copper mould casting under pressure consist of α-Mg, Mg2Sn, Mg51Zn20 and Mg32(Al,Zn)49. The higher cooling rate promotes the formation of the grain boundary compounds, while the applied pressure has an inhibiting effect on it. The alloy prepared by water-cooling copper mould casting under pressure is characteristics of the finest grain size, the smallest dendrite arm spacing and the much finer, well-distributed second phases among the five as-studied alloys, exhibiting the optimal mechanical properties, with the ultimate tensile strength, the yield strength and elongation to rupture of 224MPa, 157MPa and 16.1% respectively. In comparison with the alloy prepared by steel mould casting with no applied pressure, the ductile fracture characteristics of void coalescence is dominant for the alloy prepared by water-cooling copper mould casting under pressure.

A two-step surface treatment, combining fluoride pretreatment and anodic electrophoresis deposition of waterborne acrylic resin, for Mg–Li–Al–Ce alloy

In order to improve the corrosion resistance of Mg–Li–Al–Ce alloy. A new two-step surface treatment, combining fluoride pretreatment in hydrofluoric acid (HF) solution and anodic electrophoresis in waterborne acrylic resin solution, is developed for Mg–Li–Al–Ce alloy. The results of scanning electron microscopy with energy dispersion spectroscopy show that a 6μm thick fluoride film is formed on the Mg–Li–Al–Ce alloy. A compact, uniform and 56μm thick waterborne acrylic resin coating is formed on the fluoride-coated alloy. The results of electrochemical measurements show that the double-layer coating improves the corrosion resistance of Mg–Li–Al–Ce alloy.

Computational phase equilibria and experimental investigation of magnesium–aluminum–calcium alloys

Mg–Al–Ca alloys provide excellent creep resistance and castability for elevated temperature applications. Computational thermodynamics calculations and experimental investigation of the Mg–Al–Ca ternary system have validated the earlier development of creep-resistant AX52 (Mg–5Al–2Ca11All compositions in wt.% except otherwise stated.) and AX53 (Mg–5Al–3Ca) alloys. The Scheil simulation of alloy solidification has suggested key guidelines of alloy composition design in promoting the thermally stable (Mg,Al)2Ca phase, while replacing the less stable Mg17Al12 in the microstructure. The suppression of the Mg17Al12 phase can increase the solidus temperature, reduce the freezing range, and increase the latent heat during solidification, all of which contribute to improved castability in the AX53 and AX52 alloys compared with the AX51 (Mg–5Al–1Ca) alloy. The quantitative phase equilibrium data, microstructure characterization, as well as the thermal physical properties of the Mg–Al–Ca alloy system generated from this study are important basis for further optimization of alloy composition and microstructure for elevated temperature applications.

Effect of the Thermomechanical Processing on Microstructure and Properties of an Al-Ce Alloy

Effect of equal channel angular pressing (ECAP) at room temperature and subsequent annealing at temperatures ranging from 450 to 600°C on microstructure, mechanical properties and electric conductivity of an Al-8%Ce alloy was examined It was shown that Al4Ce-type eutectic particles having plate-like shape break under ECAP; distribution of the particles appears to be more homogeneous. ECAP leads to about two-fold increase in yield stress (YS) and ultimate tensile strength (UTS); ductility and electric conductivity decrease significantly. Under following annealing, the spheroidizing and coagulation of Al4Ce-type particles occur extensively resulting in decreased strength and increased electric conductivity and ductility.

Role of Rare Earth Ions in Anodic Gate Dielectrics for Indium-Zinc-Oxide Thin-Film Transistors

Al-alloys and their anodic oxides were used as the gate and the gate dielectric, respectively, for the indium-zinc-oxide (IZO) thin-film transistors (TFTs). The influence of the Al-alloys on the performances of the IZO-TFTs was investigated. It was found that the hillock formation could be completely suppressed by doping neodymium (Nd) or cerium (Ce) into Al. However, the mobility of the IZO-TFT with Al-Ce gate was only 2 × 10−4 cm2 V−1 s−1, about five orders lower than that of the IZO-TFT with Al-Nd gate (11.6 cm2 V−1 s−1). Further analysis showed that Ce3+ and Ce4+ ions were existence in the oxide film obtained by anodizing Al-Ce alloy, and they would diffuse into IZO film. The Ce4+ ion could act as an electron trap due to its strong oxidizability, so the IZO-TFTs with Al-Ce gate would experience seriously degradation. In the case of the oxide film obtain by anodizing Al-Nd alloy, only Nd3+ were found, which was stable and would not produce electron traps. Moreover, the existence of Nd would suppress undesirable free electron formation in the channel, resulting in low off-current, low subthreshold swing, little hysteresis, and high electrical stability under gate bias stress.

Magnetic nanoscale laminates with tunable exchange coupling from first principles

The ${M}_{n+1}$$A{X}_{n}$ (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr${}_{1\ensuremath{-}x}$Mn${}_{x}$)${}_{2}$AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomic-thin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling.

Microstructure and micromechanism maps to optimise useful deformation processing conditions in magnesium alloy

The present investigation examines the use of microstructure and micromechanism maps to develop a systematic understanding of the various microstructures that evolve in pure Mg and Mg–Al–Ce alloys during uniaxial compression deformation over a range of strain rates and temperatures. These maps further refine the safe deformation regimes that are predicted by dynamic materials modelling maps (or process modelling), which are based on efficiency of power dissipation for microstructure evolution η and the instability parameter Σ(). Operating mechanisms such as dynamic recrystallisation, cracking, twinning and grain coarsening are identified through careful microstructural analysis and mapped as a matrix at appropriate locations on a two-dimensional strain rate–temperature map. The study demonstrates that while conventional process maps delineate safe and unsafe working regimes based on power dissipation, it is the use of the microstructure and micromechanism maps in conjunction with the process maps that provide a more accurate and comprehensive picture of the processing window, which should be used for producing materials with certain defined end use. The process maps developed have been validated with a limited number of extrusion trials on pure Mg and Mg–Al–Ce alloys.

Study of Back Electromotive Force in the Preparation of Al-Ca Alloy by Molten Salt Electrolysis Method

Al-Ca master alloy was prepared by molten salt electrolysis method, using a mixed molten salt system of CaCl2-CaF2and feeding CaO as electrolysis material. The technological parameters such as back electromotive force (BEMF), cell voltage, and current were measured by testing device of molten salt electrolysis. The effects of current density, CaO addition, electrolysis time and feeding period on the back electromotive force in the electrolysis process are studied. The results indicate that back electromotive force increases with current density increasing, the feeding period is 30min measured by potential control method. Finally, the Al-Ca alloy with the Ca content of 11.6wt% can be obtained by electrolyzing for 1h at the current of 7A and at 740.

Hydrogen generation by splitting water with Al–Ca alloy

A new hydrogen generation material, Al–Ca alloy, is prepared by ball milling method. Results show the prepared Al–Ca alloy can react with to produce hydrogen, but its hydrogen yield is lower. NaCl addition can further greatly improve hydrogen generation of Al–Ca alloys. The amount of NaCl addition and ball milling time depends on the Ca contents of alloys. As the Ca contents of alloy increase, the amount of NaCl addition or ball milling time may be reduced accordingly. Increasing Ca contents, NaCl addition or ball milling time is beneficial to improve the hydrogen generation rate. Al–Ca alloys can react with water to produce hydrogen at the temperature ranging from 10 °C to 80 °C, and simultaneously a great amount of heat is released. With the increase of air exposure time, the dense Al 2O 3 and CaO layer formed on the surface of alloy particles will reduce the oxidation reaction rate. Chloride ions and sulfate ions can greatly decrease the induction period of hydrogen generation reaction and obviously improve hydrogen generation rate. Ca 2+ ions and Mg 2+ ions can affect the production of hydrogen due to their strong affinity to OH −, especially Mg 2+ ions which greatly decrease the hydrogen yield to 20%.

Influence of applied pressure on microstructure and tensile properties of squeeze cast magnesium Mg–Al–Ca alloy

This paper reports the effect of applied pressure on the tensile properties and the microstructure of squeeze cast Mg–5 wt.%Al–1 wt.%Ca (AX51) alloy. In this study, applied pressures from 3 to 90 MPa were considered. It was observed that the fraction of second phases and porosity level reduces with an increase in applied pressure. The tensile tests results indicate that ultimate tensile strength (UTS), yield strength (YS) and elongation ( E f) of AX51 alloy increase with increasing applied pressures. The improvement in tensile properties was attributed to the casting densification and presence of higher amount of solute in the matrix. The scanning electron microscopy (SEM) fractographs reveal that the fracture modes of the squeeze cast alloy is more ductile at higher applied pressures. The crack initiation occurred mostly in the vicinity of Mg–Al–Ca particles.

High-strength Mg–Al–Ca alloy with ultrafine grain size sensitive to strain rate

The microstructure, texture and mechanical properties of the 1 wt.% Ca-AZ31 alloy (1CaAZ31) processed by high-ratio differential speed rolling (HRDSR) were examined. After HRDSR, the grain size of the 1CaAZ31 decreased to ∼0.9 μm, and (Al, Mg) 2Ca particles were highly refined and uniformly dispersed into the matrix. The significant improvement in strength was attributed to the effective grain-size reduction. Contribution of the particle strengthening was relatively small. Strength of the ultrafine grained (UFG) 1CaAZ31 was sensitive to strain rate. As the result, the yield stress was as high as 412 MPa at 1 × 10 −1 s −1, while it was 292 MPa at 1 × 10 −5 s −1. The strain-rate-sensitivity of the UFG 1CaAZ31 was 0.031–0.041, which is about twice larger than that of its annealed counterpart having coarse grains (0.018). Uniform elongation of the UFG 1CaAZ31 was small compared to that of the coarse-grained 1CaAZ31 due to the reduced strain hardening ability, but its post-uniform elongation was large due to the increased strain-rate sensitivity.

Investigation on the nature of active species in the CeCl 3-doped sodium alanate system

CeCl 3-doped NaAlH 4 was directly synthesized in hydrogenation process using NaH/Al with 2 mol% CeCl 3 under ball-milling. X-ray diffraction was utilized to unveil the nature of cerium during NaAlH 4 synthesis process and succedent cycling. It is found that, CeCl 3 is reduced in the ball-milling process and following cycles, causing the formation of NaCl and Al–Ce alloy with a structure of CeAl 4. The catalytic enhancement arising upon doping the ball-milled CeAl 4 alloy is quite similar to that achieved in the CeCl 3-doped sodium alanate. Because the CeAl 4 dopant does not consume the effective hydrogen storage component, the CeAl 4-doped NaAlH 4 exhibits more hydrogen storage capacity. Moreover, CeCl 3-doped NaAlH 4 and CeAl 4-doped NaAlH 4 exhibit similar apparent activation energies estimated from Kissinger's method, suggesting the reactions are all determined by the same rate-limiting step. These results clearly demonstrate that the in situ formed CeAl 4 acts as active species to catalyze the reversible dehydriding/rehydriding of NaAlH 4.

Monte Carlo Simulation of Thermophysical Properties for Al-Ce Liquid Alloys

The Monte Carlo method with EAM potential is applied to simulate the liquid Al-Ce binary alloy system and the thermophysical properties including surface tension (), viscosity () and diffusion coefficient (D) of liquid Al-8at%Ce alloy are determined. The simulated  values decrease with temperature. Based on the relationship between ,  and D, the various viscosity and diffusion coefficient of liquid Al-Ce alloys under different temperatures were determined. The comparison of the simulated results with some experimental measurements is performed and discussed, indicating that the simulation method and EAM parameters in simulation are acceptable. The dependence of viscosity and diffusion coefficient of liquid Al-Ce alloys on temperature is established to be helpful in further investigation of amorphrization ability of Al-Ce alloys.

Assessment of creep rupture life of heat resistant Mg–Al–Ca alloys

Creep rupture tests were performed for three kinds of Mg–Al–Ca die-cast alloys at temperatures between 423 and 498 K, and the creep rupture lives were evaluated by using the Larson–Miller parameter (LMP). The value of LMP is uniquely described by the logarithm of the applied stress for the alloys, when the Larson–Miller constant is chosen as 20. The applied stress and the LMP value follow a linear relationship below the yield stress, which can be utilized to predict the long-term creep rupture life for the alloys under a given condition of temperature and applied stress.

Role of Oxide Particles in Aluminum Melt toward Aluminum Foam Fabrication by the Melt Route

The aim of this work is to elucidate the role and contribution of oxide particles to aluminum foam fabrication. The melts were internally oxidized by a thickening process in which pure aluminum melt was stirred with or without the addition of 1.5 wt.% calcium for maximum 25 min. After this, each thickened samples were melted again and mixed for 100 s by introducing 1.5 wt.% TiH2 as a blowing agent. In order to investigate the foam evolution, the foam samples were hold in the furnace for 50 to 500 s. The stirring torque (viscosity) of the calcium containing melt increases with thickening time and achieves the stationary value after 17 min. However, the torque of pure aluminum melt does not change during stirring. Oxides have been found on the microstructures of both stirred samples, although the content of oxides of calcium added sample is significantly more than that of pure aluminum. SEM observation results of samples thickened by calcium addition show that the melt contains calcium oxide and Al4Ca in addition to equiaxed aluminum, and the morphology of formed oxide is not granulous but wrinkled bifilm containing calcium and aluminum oxides. The oxides formed in the pure Al melt has less effect on the viscosity thus the foamability of the aluminum melt. It is found that the calcium oxides formed by stirring are responsible for the effective increase of melt viscosity. The foams using oxidized pure Al melt have dense layer at the bottom caused by drainage and coarse foam structure due to strong coalescence. In case of the Al-Ca alloy, uniform pore distribution, lack of the dense layer and homogeneous time dependent increase of the cell size were observed. Besides, the sample held for longer time has thicker cell wall at the bottom compared with that at the top. We confirmed that the oxide bifilms of Al and Ca contributes to decreased drainage rate and coalescence, namely stabilization. The insufficient amount of oxide particles in pure aluminum is the reason for the lack of stabile foam (significant drainage) in that case.