Al Ca Alloy Research Articles

Three-Dimensional Morphology of C15–Al<sub>2</sub>Ca Precipitates in a Mg–Al–Ca Alloy

The three-dimensional morphology and thickness of the C15–Al2Ca Laves phase, which precipitated within the primary α-Mg grains, were investigated for the Mg–5Al–1.5Ca alloy over-aged at 523 K for 100 h using the high-resolution transmission electron microscopy (HRTEM). The C15–Al2Ca phase precipitated with a hexagonal plate-like morphology along the (0001)α basal plane of the α-Mg matrix phase, where the sides of the hexagonal plates were parallel to the second columnar plane {1120}α of the α matrix. The typical coffee bean contrast was clearly visible around the precipitates, indicative of coherent precipitation of the C15–Al2Ca phase. The thickness of the C15–Al2Ca precipitates, which corresponds to the six layers of (111)C15 plane composed of Ca atoms, was evaluated to be approximately 1.5 nm.

Dislocation analysis of a Mg–Al–Ca alloy by transmission electron microscopy

The dislocation structure was analyzed in a Mg–4.98Al–1.46Ca (mass%) alloy using invisible criterion with transmission electron microscopy. Basal and non-basal segment of dislocation induced during die-casting is determined as much 〈a〉 and a few 〈a+c〉 dislocation. After the aging at 523 K for 10 h and tensile deformation at 473 K, only basal 〈a〉 dislocation can be observed. This dislocation structure is not observed in crept specimens, which support the difference in dominant strengthening mechanism between creep and tensile deformation.

Effects of Ca/Al ratio and extrusion process on Mg–Al–Ca alloys to produce a high toughness in-situ composite

ABSTRACTThe microstructures and tensile properties of Mg–Al2Ca–Mg2Ca in situ composites (Mg–17Al–8Ca, Mg–14Al–11Ca and Mg–12.5Al–12.5Ca) with different Ca/Al ratios have been studied in both as-cast and extruded conditions. The results indicated that by increasing Ca/Al ratio, new Mg2Ca intermetallic introduces to the Al2Ca phase in eutectic structure. Computer-aided cooling curve analysis confirmed the formation of these phases during solidification. Extrusion process not only altered the size of large bulk Al2Ca intermetallic, but also changed the size and morphology of intermetallics in eutectic structure considerably. The results showed that with increasing Ca/Al ratio, tensile properties of cast composites changes slightly, but significant enhancement is observed after extrusion process. The strength and elongation values of Mg–12.5Al–12.5Ca (Ca/Al = 1) alloy improved from 166 MPa and 2% in as-cast condition to 465 MPa and 12% in hot-extruded condition. The reason for the improved toughness may be attributed to the formation of finer and well-dispersed distribution of hard (Al2Ca) and ductile (Mg2Ca) phases. It was found that hot extrusion easily deforms ductile Mg2Ca phase in comparison with Al2Ca phase. In as-extruded condition, there are more very fine dimples than as-casted condition because extrusion process leads to formation of fragmented tiny particles and more uniformity distribution of Al2Ca particles.

Phase Diagram of the Al-Ca-Fe-Si System and Its Application for the Design of Aluminum Matrix Composites

The phase composition of aluminum alloys in the Al-Ca-Fe-Si system, including the distribution of phases in the solid state and solidification reactions, has been studied. It is shown that the addition of iron and silicon to Al-Ca alloys leads to the formation of ternary Al2CaSi2 and Al10CaFe2 compounds. The equilibrium between these compounds implies the occurrence of the quaternary L → Al + Al4Ca + Al2CaSi2 + Al10CaFe2 eutectic reaction. The alloys near this eutectic have the best structure, which is typical of aluminum matrix composites. It is shown that Al-Ca alloys can have high manufacturability during both shape casting and rolling. This is due to the combination of a narrow temperature range of solidification and a favorable morphology for the eutectic, which has a fine structure. The combination of the mechanical and physical properties of the Al-Ca eutectic-based alloys significantly exceed those of branded alloys based on aluminum–silicon eutectics.

Ageless Aluminum-Cerium-Based Alloys in High-Volume Die Casting for Improved Energy Efficiency

Strong chemical reactions between Al and Ce lead to the formation of intermetallics with exceptional thermal stability. The rapid formation of intermetallics directly from the liquid phase during solidification of Al-Ce alloys leads to an ultrafine microconstituent structure that effectively strengthens as-cast alloys without further microstructural optimization via thermal processing. Die casting is a high-volume manufacturing technology that accounts for greater than 40% of all cast Al products, whereas Ce is highly overproduced as a waste product of other rare earth element (REE) mining. Reducing heat treatments would stimulate significant improvements in manufacturing energy efficiency, exceeding (megatonnes/year) per large-scale heat-treatment line. In this study, multiple compositions were evaluated with wedge mold castings to test the sensitivity of alloys to the variable solidification rate inherent in high-pressure die casting. Once a suitable composition was determined, it was successfully demonstrated at 800 lbs/h in a 600-ton die caster, after which the as-die cast parts performed similarly to ubiquitous A380 in the same geometry without requiring heat treatment. This work demonstrates the compatibility of Al REE alloys with high-volume die-casting applications with minimal heat treatments.

The Influence of FeO on the Reaction between Fe–Al–Ca Alloy and Al2O3–CaO–FeO Oxide during Heat Treatment at 1473 K

Oxygen diffusion from oxides to an alloy during heat treatment could influence the properties of the alloy and oxides. To clarify the influence of FeO on the solid-state reactions between Al2O3–CaO–FeO oxide and Fe–Al–Ca alloy during heat treatment at 1473 K, three diffusion couples with different FeO concentrations in the oxide were produced. The diffusion couples were subjected to several procedures successively including an oxide pre-melting experiment using a confocal scanning laser microscope to obtain good contact between the alloy and oxide, vacuum sealing to protect the specimens from oxidation, heat treatment, and electron probe X-ray microanalysis. The effects of the FeO content in the oxide on the morphology of the interface between the alloy and oxide, change of elements in the alloy, widths of the particle precipitation zone (PPZ) and aluminum-depleted zone (ADZ), and size distribution of the particles in the alloy, were investigated and discussed. Based on the Wagner equation of internal oxidation of metals, a modified dynamic model to calculate the PPZ width was established to help understand the mechanism of the solid-state reactions and element diffusion between the Fe–Al–Ca alloy and Al2O3–CaO–FeO oxide with different FeO concentrations.

Evaluation of an Al-Ce alloy for laser additive manufacturing

This study focuses on the development of a design methodology for alloys in AM, using a newly developed Al-Ce alloy as an initial case study. To evaluate the candidacy of this system for directed energy deposition processes, single-line laser melts were made on cast Al-12Ce plates using three different beam velocities (100, 200, and 300 mm/min). The microstructure was evaluated in the as-melted and heat treated conditions (24 h at 300 °C). An extremely fine microstructure was observed within the melt pools, evolving from eutectic at the outer solid-liquid boundaries to a primary Al FCC dendritic/cellular structure nearer the melt-pool centerline. The observed microstructures were rationalized through the construction of a microstructure selection map for the Al-Ce binary system, which will be used to enable future alloy design. Interestingly, the heat treated samples exhibited no microstructural coarsening.

Underpotential Deposition of Al-Ce Alloys at an Al Electrode from LiCl-KCl-CeCl3 Melts

Electrochemical behavior of Ce(III) and underpotential deposition of Al-Ce alloys were investigated at an Al active electrode in LiCl-KCl-CeCl 3 melts. Compared with the cyclic voltammetry curves on a Mo electrode, the redox potential of Ce(III)/Ce at the Al electrode is more positive; there are two new plateaus between the deposition plateau of Al and Ce metal by open circuit chronopotentiometry, which means two kinds of intermetallic compounds. All above show Ce(III) forms intermetallic compound by underpotential deposition electrochemically. Furthermore, it is also confirmed by Al-Ce alloys, which are obtained at the Al active electrode in LiCl-KCl-CeCl 3 melts after potentiostatic deposition under the same condition. The formation of AlCe and AlCe 3 is illuminated by X-ray diffraction (XRD). The reasons of AlCe and AlCe 3 formation were explained by XRD and phase diagram of Al-Ce. The standard Gibbs free energies of AlCe and AlCe 3 formation were calculated by XRD and open circuit chronopotentiometry. The analysis of scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) reveals that cerium exists at the surface of Al electrode to form an Al-Ce alloys layer, which is about 28 μm in thickness, and evenly coated the Al electrode.

Cell Structure Evolution of Aluminum Foams Under Reduced Pressure Foaming

Ti-H particles are used to increase the gas content in aluminum melts for reduced pressure foaming. This paper reports on the RPF process of AlCa alloy by adding TiH2, but in smaller amounts compared to traditional process. TiH2 is completely decomposed by stirring the melt, following which reduced pressure is applied. TiH2 is not added as the blowing agent; instead, it is added for increasing the H2 concentration in the liquid AlCa melt. It is shown that pressure change induces further release of hydrogen from Ti phase. It is also found that foam collapse is caused by the fast bubble coalescing during pressure reducing procedure, and the instability of liquid film is related to the significant increase in critical thickness of film rupture. A combination of lower amounts of TiH2, coupled with reduced pressure, is another way of increasing hydrogen content in the liquid aluminum. A key benefit of this process is that it provides time to transfer the molten metal to a mold and then apply the reduced pressure to produce net shape foam parts.

Mg–Al–Ca系合金を真空蒸留した高純度マグネシウムの製造とその押出材の耐食性と引張特性

In order to improve the property of high purity magnesium produced from Mg–Al–Ca alloy, vacuum distillation and extrusion method has been employed. The vacuum distillation with the raw material temperature of 600°C, condenser temperature of 310–350°C, and purification time at 8 h is able to control the amount of impurity such as Fe, Ni and Cu less than 0.0003%. The efficiency of purification and condenser condensate of alloy is achieved nearly 90%. The corrosion rate of high purity magnesium after extruded at 300–375°C and extrusion ratio of 100 is about 0.4 mm/y, which is better than that of purity 99.99% magnesium. Further, the tensile strength of extruded specimen is about 200 MPa, and the elongation is about 15%.

Extraction of lithium from salt lake brine by aluminum-based alloys

Salt lake brine was reacted with activated aluminum-based alloys and lithium was precipitated. The effects of aluminum-based alloys on precipitating lithium were investigated and the reasonable alloy used to extract lithium from brine was obtained. The effects of the mole ratio of Al to Li and Ca content of Al–Ca alloy, the initial concentration of lithiumion ion in solution, reaction temperature and reaction time on the adsorption rate of lithium were studied, and the optimized process parameters were determined. The results show that the mole ratio of Al to Li and Ca content of Al–Ca alloy and reaction temperature have great influences on the precipitation rate of lithium. The precipitation rate of lithium reaches 94.6% under the optimal condition, indicating that Al–Ca alloy is suitable for the extraction of lithium from salt lake brine.

Characteristics of dynamically formed oxide films in aluminum–calcium foamable alloys

Characteristics of dynamically formed oxide layers in Al–Ca alloys containing up to 2.0 wt.% calcium, which are commonly used in manufacturing Alporas closed-cell aluminum foams, were investigated using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). A recent modern technique known as oxide-metal-oxide (OMO) sandwich was applied to prepare the samples containing 0, 0.5, 1, 1.5, and 2 wt.% calcium.The results of the intensive research studies clarify that the presence of the calcium in the aluminum intensifies the oxidation of the alloys and subsequently the thickness of the oxide layers. In addition, increasing the calcium content led to an obvious change in the oxidation behavior of the alloys as well as the morphology of oxide layers. The alloys containing less than 1 wt.% calcium, formed nano-sized calcium aluminate particles. These particles were generally formed in regions located between the grain boundaries of solidified alloy and the covering alumina layer where caused the destruction sites in the deformed alumina layer. The increase of the calcium contents of the alloy more than 1 wt.%, not only intensified the formation of under-layer nano-sized calcium aluminate particles but also changed the morphology and thickness of the covering oxide layers. In alloys containing 1 wt.% calcium or higher, the oxide layers were consisted of tile-like, thick, highly brittle and scrappy calcium aluminate layer. These oxide layers can interfere with the molten alloys as a result of the stirring process and enhance the apparent viscosity of the alloys.

Microstructure and mechanical properties of Mg–Al–Ca alloy influenced by SiCp size

Mg–Al–Ca matrix composites reinforced with three sizes (1μm, 5μm, and 10μm) of SiCp were fabricated by stir casting. Then the as-cast ingots were extruded at 400°C with the ratio of 16 at a constant ram speed of 3mm/s. The results indicate that addition of only ~1vol% SiCp is propitious to promote the nucleation and refinement of Al2Ca phase, which can eliminate the Al2Ca phase's network distribution that appeared in as-cast Mg–Al–Ca alloy. But the nucleation of Al2Ca phase strongly depends on SiCp size. Al2Ca phase nucleates at 5μm and 10μm SiCp, however, it nearly cover the whole particle as the SiCp size decreases to 1μm. Besides, the existence of 5μm and 10μm SiCp is propitious to the fracture of Al2Ca phase, however, the 1μm SiCp seems ineffective to Al2Ca phase during hot extrusion process. Compared with monolithic Mg–Al–Ca alloy, the as-extruded SiCp/Mg–Al–Ca composites exhibit much higher YS, UTS and θ value. Even though the YS and θ value increase with decreasing SiCp size, the UTS does not change linearly with them and the reasons are given and analyzed.

Influence of the Al2Ca phase on microstructure and mechanical properties of Mg–Al–Ca alloys

In this work, the microstructure and mechanical properties of Mg–Al–Ca alloys containing different contents (1, 2, 4 and 6 wt.%) of the Al2Ca phase have been investigated. The results show that the Al2Ca phase formed along the interdendritic regions in as-cast alloys. As the content of the Al2Ca phase is 4 wt.%, the finest microstructure of the as-cast Mg–Al–Ca alloy is observed. After hot extrusion, the extruded Mg-2.32Al-1.7Ca (Mg-4Al2Ca) alloy exhibits superior mechanical properties with the UTS of 324 MPa, the YS of 275 MPa and the elongation of 10.2%. This is mainly attributed to the combined effects of fine dynamically recrystallized grains, nano-scale plate-like Al2Ca precipitation and high density of submicron Al2Ca particles dispersion in the α-Mg matrix, respectively.

Rotation contour contrast reconstruction using electron backscatter diffraction in a scanning electron microscope

The microstructure of a deformed Mg–Al–Ca alloy was imaged using an electron-beam energy of 20 keV in a cold field-emission scanning electron microscope. The backscattered electron (BSE) micrographs showed a non-uniform contrast, the simplest being in the form of parallel contours inside a number of grains. This contrast is described as rotation contour contrast (RCC) and is attributed to local rotation of the crystal during the deformation of the grain. A model is presented to relate the rotation of crystal planes about one rotation axis to the channeling contrast in the channeling pattern and, consequently, to RCC in the BSE micrograph. This model was validated with the electron backscatter diffraction technique such that the RCCs in the BSE micrograph were reconstructed using the electron backscatter diffraction pattern intensities. The appearance of the RCCs was attributed to the change in the electron-beam position across a Kikuchi band due to local crystal rotation.

Microstructures and mechanical properties of Mg–Al–Ca alloys affected by Ca/Al ratio

The Mg–Ca alloys with 2wt%, 3wt%, 5wt% Al content were fabricated in this paper. After be extruded at 673K with the ratio of 16:1, the microstructures and mechanical properties of the alloys influenced by Ca/Al ratio were investigated.Results showed that the category and amount of precipitated secondary phase were influenced obviously by Ca/Al ratio, which changed from Mg2Ca and (Mg, Al)2Ca to Al2Ca as the Ca/Al ratio decreased from 1 to 0.4. Even though the secondary phase was cracked after the application of hot extrusion, the amount, size and distribution of secondary phase were strongly dependent on Ca/Al ratio. The basal plane texture was found in all the as-extruded alloys, the I(101¯0)/I(101¯1) and I(0002)/I(101¯1) values demonstrated different changing tendencies with the variation of Ca/Al ratio. All the UTS, elongation and strain hardening rate of the as-extruded alloys increased with decreasing Ca/Al ratio, however, the YS exhibited the inverse variation tendency. A significant stagnation point was found in the θ-(σ-σ0.2) curve as the Ca/Al ratio is 1, which becomes unobvious with decreasing Ca/Al ratio. The reasons are given and analyzed.

Electrochemical extraction of cerium and formation of Al-Ce alloy from CeO2 assisted by AlCl3 in LiCl-KCl melts

This work presents an electrochemical extraction of cerium and synthesization of Al-Ce alloy in LiCl-KCl melts on Mo and Al electrodes by chlorination of CeO2 using AlCl3 at 873 K. The cyclic voltammogram on Mo electrodes in LiCl-KCl-CeO2 melt showed no obvious reduction wave other than the reduction of Li(I). After the addition of AlCl3, the signals of the reaction of Ce(III)/Ce(0) and the synthesization of Al-Ce and Al-Li alloys were investigated by cyclic voltammetry, square-wave voltammetry, open-circuit chronopotentiometry and chronopotentiometry. These results indicated that AlCl3 can chloridize CeO2 and that it is possible to extract cerium and form Al-Ce and Al-Li-Ce alloys in LiCl-KCl-CeO2-AlCl3 melts. According to potentiostatic electrolysis, only the Al4Ce layer coated the Al electrodes. According to galvanostatic electrolysis, Al-Ce (Al4Ce, Al3Ce, and Al92Ce8), Al2Li3, and Al phases were formed on Mo electrodes, and the content of cerium in the Al-Li-Ce alloys was more than 17 wt%.

Microstructure, mechanical properties, corrosion behavior and cytotoxicity of Mg–Zn–Al–Ca alloys as biodegradable materials

Recently, considerable attentions have been paid to alloy Mg–4Zn–0.2Ca for biomedical applications due to its suitable biocompatibility and acceptable mechanical properties. In this work, the effects of the addition of different amounts of Al on microstructure, mechanical properties, degradation behavior, and biocompatibility of this alloy were investigated. The corrosion behaviors of the alloys were investigated through polarization tests, chronoamperometry analysis, immersion tests, and EIS experiments. The mechanical properties were analyzed by using tensile tests and compression tests. The results showed that the addition of Al up to 3wt.% considerably modifies the degradation behaviors and the mechanical properties of the alloys due to its positive effects on microstructure refinement. On the other hand, the addition of more quantities of Al leads to the formation of considerable amounts of secondary phases in the grain boundaries of the alloys, leading to noticeably deteriorated properties. Mechanical tests showed that the addition of Al (up to 3wt.%) increases the UTS of the alloys from 157MPa to 198MPa. Moreover, in vitro corrosion tests in SBF solution revealed that with the addition of Al up to the above mentioned value, the corrosion current densities of the alloys decrease from 134μAcm−2 to 22μAcm−2, and Mg–4Zn–3Al–0.2Ca exhibited the lowest obtained degradation rates in different immersion and electrochemical experiments. Cytotoxicity assessments also indicated the good biocompatibility of this alloy, making it a suitable candidate for further considerations as a degradable metallic biomaterial.

Effects of Nd on microstructure and mechanical properties of Mg–Al–Ca alloy

Effects of Nd additions (0–4 wt-%) on microstructures and properties of Mg–Al–Ca alloy at room temperature and 150°C have been investigated. The results showed that Mg–6Al–2Ca alloy consisted of α-Mg matrix, Mg17Al12, Mg–Ca and Al–Ca phases. The amount of Al–Nd phase increases with the increasing of Nd content while that of Mg17Al12 decreases. On the other hand, Nd refines the microstructure of as cast and extruded alloys. The ultimate strength and yield strength of experimental alloys are improved with the addition of Nd, and the largest values are 319 and 210 MPa respectively at room temperature. When the temperature was elevated to 150°C, with the increasing of Nd, ultimate strength and yield strength of experimental alloys are first increased and subsequently decreased. Mg–6Al–2Ca–xNd alloy has the best ultimate strength and yield strength at 150°C, which reaches 265 and 179 MPa respectively when the content of Nd reached 3%.

The Effect of Magnesium Addition on the Microstructure & Compressive Deformation Behavior of Al-Ca Alloy

The Al-Ca-Mg alloys containing varying amount of Mg are used to study the effect of Mg addition on their microstructure and deformation behavior at varying strain rate (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 were also determined for each material at different strain rates. The elastic limit decreases with increases in strain rate. The strain rate sensitivity m is found to be negative at a flow strain and invariant to the strain rate. Its microstructure reveals that the microstructural characteristics changes with Mg addition. The variation of microstructural features primarily leading to the variation of deformation behavior.