Al Ca Alloy Research Articles

Review of Laser Powder Bed Fusion’s Microstructure and Mechanical Characteristics for Al-Ce Alloys

As a new alloy manufacturing method that can break through the limitations of molds to manufacture fine parts, laser powder bed fusion has recently become a common process for producing aluminum alloys. In the fields of aerospace or automotive, aluminum alloys with both good printability and good mechanical performance in high-temperature conditions are greatly demanded, and the Al-Ce alloy is one of the alloys with significant potential. Therefore, systematic research on the additive manufacturing of Al-Ce alloys is still being explored. Herein, we review the recent progress and current status of laser powder bed fusion-produced Al-Ce alloys, giving our opinions on the development of this alloy system. Element composition, alloy powders, laser powder bed fusion parameters, microstructures, and mechanical properties at room temperature and high temperatures are summarized. The choice of alloying strategies is crucial for a specific mechanical improvement of the Al-Ce alloys. Finally, the details of the Al-Ce alloys manufactured via laser powder bed fusion are presented.

Effect of thermomechanical processing on mechanical properties and the microstructure of binary Al-Ce alloy

A new generation of Al alloys based on the Al-Ce system, with microstructure and properties weakly sensitive to elevated temperatures, is being developed for applications such as thermal engine blocks and supersonic aircraft fuselage components. Cast Al-Ce binary alloys with 4, 10 and 16 wt% Ce were produced by slab casting and further processed by extrusion. Extrusion produces a highly refined microstructure resulting in a twofold increase in strength (tensile strength of 228 MPa at room temperature). We show that the Al-10Ce is highly stable (more than 99 % strength retention after 300 °C 100 h exposure), far superior to high temperature grade Al alloy AA2618. The extruded Al-10Ce also shows a room temperature ductility of more than 20 %, with a fracture toughness of 55.42 kJ/m2 that does not degrade after high temperature exposure (97.6 % toughness retention after 300 °C 100h exposure). Results from testing at different temperatures are also reported.

Microstructural refinement of an Al-Ce-Mg alloy via Shear Assisted Processing and Extrusion

Al-Ce alloys have attracted recent interest because of their high thermal stability due to the low solubility of Ce in the Al matrix. The Al11Ce3 eutectic phase gives excellent strain hardening behavior and moderate high-temperature strength in the as-cast state. However, its strengthening effect is limited by its coarse as-cast structure. Therefore, alternative manufacturing methods such as additive manufacturing or equal channel angular pressing have been applied to refine the Al11Ce3 phase to good effect. However, these techniques are both expensive and time-consuming. Therefore, this study aims to use Shear Assisted Processing and Extrusion (ShAPE), an emerging solid phase processing technique that is more easily scalable than the previously mentioned methods. ShAPE can produce useful cross-sections of an Al-8Ce-4Mg alloy while refining the Al11Ce3 phase to produce a higher strength material. It was found that a low temperature ShAPE process can improve the room temperature yield strength by ∼60 % compared to a binary Al-4Mg alloy. Additionally, the high-temperature yield strength of the Al-Ce alloys increased by 20 %, with a simultaneous 15 % improvement in ductility compared to the binary Al-Mg alloy. These results highlight the potential for ShAPE as a processing technique for Al-Ce alloys.

Effect of eutectic microstructure on load transfer and creep resistance in Al-Ce alloys

This study investigates the compressive creep response of hypo- and near-eutectic Al-Ce alloys via finite-element modeling (FEM), by considering the composite response of a weak, fast-creeping Al matrix containing slow-creeping Al11Ce3 eutectic reinforcement. In the as-cast microstructure of an eutectic Al-12.5 wt%Ce alloy, the Al11Ce3 eutectic phase is lamellar, regardless of the various cross-sectional geometries (Chinese-script, fish-bone, and comb-like). FEM models based on these various lamellar microstructures investigate the effect of Al11Ce3 reinforcement volume fraction, orientation, and geometry on load transfer performance between matrix and reinforcement during creep deformation. FEM predicts that, when the lamellar Al11Ce3 phase is continuous along the loading direction (where load transfer is most effective), the creep resistance of the alloy is barely affected by cross-sectional geometry of the Al11Ce3 reinforcement or by the solid-solution strengthening of the Al matrix, at constant Al11Ce3 volume fraction. However, alloy creep resistance and load transfer between phases are significantly reduced when applying load parallel to aligned, discontinuous lamellae, and they can be improved by matrix solid-solution strengthening. Furthermore, Al11Ce3 short plates (as created in Al-12.5Ce by coarsening of lamellae upon over-aging at 590 °C/24 h) provide the least creep resistance and load transfer. Lastly, multi-colony FEM models are created by combining colonies with various lamellar orientations to approximate the creep performance of polycrystalline hypo- and near-eutectic alloys which, when compared to experimental data for hypoeutectic Al-7Ce and for near-eutectic Al-(10–13)Ce, provide better predictions than single-colony FEM models or analytical solutions.

Microstructure and mechanical properties of a low-alloyed Mg–Zn–Al–Ca alloy: Effect of extrusion speed

A low-alloyed Mg-1.2Zn-0.6Al-0.1Ca (wt.%) alloy was extruded at 200 °C with different ram speeds (0.5–4.0 mm/s), and the microstructure and mechanical properties were studied systematically. Heterostructures with fine dynamic recrystallized (DRXed) grains and coarse unDRXed grains were achieved at lower ram speeds of 0.5 mm/s and 1.0 mm/s, and fully-DRXed microstructure was attained at 4.0 mm/s. Increasing the extrusion speed resulted in an increase in DRXed grain size from 0.9 μm to 3.8 μm, and a transformation of the DRXed texture component from <10 to 10>−<11–20> to a new orientation that deviated by approximately 14°. The sample extruded at 0.5 mm/s presented an excellent tensile yield strength (TYS) of 369 MPa along with a 7.8% elongation, which was mainly due to the high hetero-deformation induced (HDI) strengthening provided by its heterostructures. Increasing ram speed resulted in an improved elongation despite a decreased TYS. The reasons for the decreased strength with increasing extrusion speed were mainly associated with grain growth, reduced dislocation density and weakened HDI strengthening. The reasons for the improved ductility with increasing extrusion speed were largely due to the increased DRXed grains fraction with soft orientations.

Nucleation and growth behavior of primary Al11Ce3 intermetallic compounds during solidification in a hypereutectic Al–Ce alloy

In this study, the nucleation and growth mechanisms of Al11Ce3 intermetallic compounds (IMCs) in a hypereutectic Al–Ce alloy during solidification were investigated through synchrotron radiation X-ray real-time imaging. The results showed that Al11Ce3 IMCs nucleate and grow from the melt as the primary phase at the initial stage of solidification. Growth preferred orientations were observed in two opposite directions, resulting in an I-shaped growth pattern. Based on the minimum energy criterion, the morphology of Al11Ce3 IMCs displayed either hollow cubic tubes or grooves. The nucleation and growth rates of Al11Ce3 IMCs gradually decreased over time, owing to the variations in the Ce concentration in the melt and the undercooling. The nucleation and growth characteristics of Al11Ce3 IMCs can provide the theoretical basis for optimization on the performance of Al–Ce alloys.

Hypereutectic Al-Ce-X (X=Mn, Cr, V, Mo, W) alloys fabricated by laser powder-bed fusion

We characterize the microstructures and high-temperature mechanical properties of Al-2Ce and ternary Al-2Ce-1X (at.%) alloys fabricated by laser powder-bed fusion (LPBF), where X = Mn, Cr, V, Mo, and W are slow-diffusing transition metals. All ternary alloys show a hypereutectic microstructure in the as-LPBF state, containing an interconnected network of eutectic Al11Ce3 phases (∼10 vol.%) and an additional population of submicron, equiaxed Al20CeX2 primary precipitates (∼10 vol.%) which are isomorphous among these five alloys. Similar microstructures are present in arc-melted rods and atomized powders but are coarser due to the slower cooling rates in these processes. The hardness of the as-LPBF ternary Al-Ce-X alloys (1300–1400 MPa) is higher than that of the binary Al-Ce alloy (∼1100 MPa) due to the higher volume fraction of strengthening phases. Furthermore, during exposure at 400 °C for up to three months, greater hardness retention is achieved in the ternary Al-Ce-X alloys (65–75%) than in the binary Al-Ce alloy (∼55%), which is attributed to the extreme coarsening resistance of the Al20CeX2 precipitates imparted by the very slow-diffusing ternary solute. These coarsening-resistant Al20CeX2 precipitates also substantially improve alloy creep resistance, increasing the threshold stress for dislocation creep at 300°C from ∼32 MPa for the binary Al-Ce alloy to ∼77–100 MPa for the ternary Al-Ce-X alloys, and at 400°C from <10 MPa for the binary Al-Ce alloy to >40 MPa for the ternary Al-Ce-V alloy.

Atomic-scale compositional complexity ductilizes eutectic phase towards creep-resistant Al-Ce alloys with improved fracture toughness

Hierarchical microstructures spanning from micro-sized eutectic structure to nano-sized precipitates are promisingly engineered in lightweight Al alloys to improve the high-temperature creep resistance that is increasingly required for rapid industrial development. However, the intrinsically-brittle eutectic phase is ready to fracture upon applied loading, which, dramatically reducing room-temperature ductility and fracture toughness, greatly hampers practical applications of the creep-resistant Al alloys. Here, through the combination of Sc microalloying with sub-rapid solidification, we observe the ductilization of Al11Ce3 eutectic phase in cast heat-resistant Al-Ce-Sc alloys due to the formation of atomic-scale compositional complexity. High-concentration Sc atoms are frozen within the Al11Ce3 intermetallic phase by the sub-rapid solidification, which then assemble into unusual atomic-scale compositional dipoles with the Sc atoms enriched at one pole and the Al atoms at the opposite during subsequent heat treatment. The dispersed Sc-Al compositional dipoles induce local lattice distortions that stimulate dislocation activities, as temporally and spatially visualized by in-situ neutron diffraction tensile test and microstructural characterizations. The unexpected plastic deformation triggered in Al11Ce3 improves the deformation compatibility between the eutectic phases, enabling the sub-rapidly-solidified Al-Ce-Sc alloy to reach a room-temperature tensile elongation 3 times and fracture toughness over 8 times of its counterpart derived from traditional solidification. In addition, the sub-rapidly-solidified Al-Ce-Sc alloy exhibits an excellent creep resistance at 300 °C, achieving a tensile creep stress threshold of ∼ 70 MPa. These findings provide new perspectives on the design of ductile intermetallic phases and the development of creep-resistant Al alloys with application-level ductility.

Effect of Laves Phases on Creep Strength for a Mg–Al–Ca Alloy

Effect of Laves Phases on Creep Strength for a Mg–Al–Ca Alloy

Schematic diagram illustrating the corrosion reaction in Mg–Li–Al–Ca alloy with and without β-Li phase

The effect of Li on the microstructure and corrosion behavior of extruded Mg-xLi-3Al-0.4Ca (x = 4,5,6,7) alloys were investigated by hydrogen evolution, potentiodynamic polarization measurement and electrochemical impedance spectroscopy measurement. The single-phase 4Li alloy with the largest α-Mg grain size and the strongest basal texture intensity exhibits the best corrosion resistance in 3.5 wt% NaCl solution. The duplex 6Li and 7Li alloys contain a protective LiOH film in the corrosion products, giving them better corrosion resistance than 5Li alloy. This study provides a new insight for the design and preparation of Mg–Li alloys with high corrosion resistance.

An efficient method of preparing Si–Fe–Al–Ca alloy from coal gasification fine slag via plasma smelting and alternating current magnetic field

It is of great significance to solve the environmental problems caused by the unreasonable treatment of coal gasification slag. This study successfully produced Si–Fe–Al–Ca alloy from low-carbon fine slag with petroleum coke as reducing agent in a plasma furnace with an alternating current magnetic field, which solved the problem of the high reactivity requirement of carbon reductant for plasma smelting. The optimum carbon content of the mixed low-carbon fine slag and petroleum coke is 105% of the theoretical value. As the strength of the alternating current magnetic field increased (from 0% to 100% of the maximum power), the yield of the alloy (from 25.46% to 58.19%) and the recovery ratios of each element (Si, Fe, Al, Ca, Ti) increased. In addition, as the magnetic field strength increased, the pores inside the alloy became smaller, the composition of the alloy became more homogeneous, and a better separation of the alloy from the slag was observed. The main composition of the alloy at the strongest alternating current magnetic field is Si: 51.14 wt%, Fe: 28.41 wt%, Al: 9.14 wt%, Ca: 7.15 wt%, Ti: 2.03 wt%. We attribute the enhanced smelting effect of the alternating current magnetic field to the resistive heat and Lorentz force produced by the induced current. In addition, the skin effect concentrated the induced current on the surface of the oxide particles and carbon particles, which increased the temperature of the reaction interface and promoted the carbothermal reduction reaction.

Sub-Rapid-Solidification Dominated Microstructure Modification and Strength Increment for Wire-Arc Directed Energy Deposited Al-Ce-Mg Alloys

Conventional cast Al-Ce alloys are challenged by the increasing demand for improved mechanical properties. To address this issue, in this study, wire-arc directed energy deposition (WA-DED) is employed for the fabrication of Al-15Ce-3Mg (wt%) alloy components. We aimed to tune the microstructure and mechanical properties via the inherent sub-rapid-solidification effect of WA-DED. In addition to significant microstructure refinement, a decrease in arc heat input leads to a larger cooling rate, up to 346 °C/s, and triggers the transition from hypereutectic to near-eutectic α-Al/Al11Ce3 microstructures with the suppression of primary Al11Ce3 intermetallics. Such microstructural modification improves the mechanical properties, resulting in higher yield and ultimate tensile strengths than those of the as-cast counterpart alloy. The fracture process involves the formation of dimples around Al11Ce3, cracking of large Al11Ce3 particles, and growth, merging, and fracture of pores. The strength increment is mainly contributed by particle-size strengthening mediated by microstructure refinement as well as the targeted formation of near-eutectic α-Al/Al11Ce3 microstructures.

Impacts of aluminum-cerium alloy deployment on different cerium commodities

An imbalance problem exists in the rare earth element (REE) market with cerium and lanthanum being more abundant and less valuable than REEs used in permanent magnets such as neodymium, praseodymium, and dysprosium. Research has been conducted on new applications for abundant REEs to improve mining economics. However, potential market impacts of these applications on individual REE commodities are unknown. A system dynamics model was built to investigate the impacts of a new aluminum-cerium (Al–Ce) alloy that can theoretically utilize three separate cerium forms: cerium carbonate, cerium oxide, or cerium metal. Cerium carbonate currently possesses the lowest price of the three available forms making it initially the most favorable choice. However, model results showed that cerium oxide could provide the best economics for future Al–Ce alloy deployment because its larger market size buffers major shocks to price.

The Beneficial Effect of Iron in Aluminum-Cerium-Based Cast Alloys

Iron (Fe) has been considered a major impurity since it is detrimental to the mechanical properties of many cast aluminum alloys due to the formation of Fe-containing brittle intermetallic phases. Fe is found naturally as an impurity in bauxite ore, resulting in Fe contamination of aluminum alloys with increasing contamination from current recycling practices. The Al–Ce–Fe system was investigated using CALPHAD (CALculation of PHAse Diagrams) modeling and experimental casting techniques. It was found that additions of Fe to the Al–Ce system are beneficial to the strength (slightly) and ductility (significantly) of the ternary alloys, which is attributed to the formation of fine metastable Al8CeFe2 phase with aggregate morphology and equilibrium Al10CeFe2 phase, suppressing coarse proeutectic Al11Ce3 phase in near-eutectic Al–Ce alloys. Heat treatment study showed that the metastable Al8CeFe2 phase transforms to predicted equilibrium Al10CeFe2 phase at 500 °C, with essentially no intermetallic or grain coarsening; thus, the alloy displayed excellent property retention. The Al–Ce–Fe alloy system offers opportunities for sustainable, recyclable alloy development using low-cost Fe and low-cost cerium (a byproduct of rare-earth extraction).

Rapid and efficient extraction of cerium by forming Al-Ce alloys in LiCl-KCl molten salts

The extraction of lanthanides in spent fuel reprocessing plays a key role in the development of nuclear energy. In this work, the extraction of the typical fissionable cerium elements has been studied by electrolytic co-reduction of Al(III) and Ce(III) in LiCl-KCl-CeCl3 molten salts assisted by KAlCl4. The electrochemical behavior of the reduction of Al(III) and Ce(III) on a molybdenum electrode was studied by cyclic voltammetry (CV), square wave voltammetry (SWV), and open circuit chronopotentiometry (OCP), and specific peaks of five Al-Ce intermetallic compounds were detected. After 2.7 h of galvanostatic electrolysis at a current density of 0.064 A cm-2, the extraction efficiency and current efficiency of Ce(III) reached 99.9 % and 91.3 % respectively. Potentiostatic electrolysis is slightly more efficient, with 99.9 % Ce(III) extraction in 3.5 h at a current efficiency of 97.8 %. The products of electrolysis are rod-shaped alloys (Al11Ce3, Al3Ce, Al2Ce), and the molten salts purified by electrolytic separation are free of impurity signals and can be reused for electrolytic refining.

Structure and Properties of Coatings Formed on Cast Al–Ca Alloys by Plasma Electrolytic Oxidation

Structure and Properties of Coatings Formed on Cast Al–Ca Alloys by Plasma Electrolytic Oxidation

Aluminothermic reduction of CeO2: mechanism of an economical route to aluminum-cerium alloys.

Cerium oxide is a low-value byproduct of rare-earth mining yet constitutes the largest fraction of the rare earth elements. The reduction of cerium oxide by liquid aluminum is proposed as an energy- and cost-efficient route to produce high-strength Al-Ce alloys. This work investigated the mechanism of a multi-step reduction reaction to facilitate the industrial adaptation of the process. Differential scanning calorimetry in combination with time-resolved synchrotron diffraction data uncovered the rate-limiting reaction step as the origin of the reported temperature dependence of reduction efficiency. This is the first in situ study of a metallothermic reaction mechanism and will serve as guidance for cost- and energy efficient industrial process control.

Microstructure and property optimization of Al–8Ce alloys: Electromagnetic stirring and Sc–Zr microalloying

To further improve the strength of an Al–Ce alloy, the effects of electromagnetic stirring treatment, Sc–Zr microalloying, and their compound action on the microstructure and properties of the Al–8Ce alloy were investigated for the first time in this study. The results show that the primary α-Al becomes coarse, the eutectic Al11Ce3 phase is refined and the lamellar spacing increases significantly due to the combined effect of forced convection of electromagnetic field and dendrite fragmentation and nucleation in Al–8Ce alloy after electromagnetic stirring treatment. After the Sc–Zr microalloying treatment of the Al–8Ce alloy, the α-Al changes from a dendritic to fine round morphology, and the eutectic Al11Ce3 phase changes from lamellar to fibrous, which is due to the heterogeneous nucleation of Al3(Sc, Zr) phase and the adsorption refinement caused by the enrichment of Sc and Zr. The optimization effect of Sc–Zr microalloying on the mechanical properties of the Al–8Ce alloy was better than that of electromagnetic stirring and their synergistic treatment. The tensile strength and yield strength of Al–8Ce alloy with Sc–Zr additions were increased from 157 MPa to 85 MPa–192 MPa and 115 MPa, respectively, by 22.3 % and 35.3 %. After aging treatment, the tensile strength (from 192 to 272 MPa) and yield strength (from 115 to 221 MPa) significantly improved owing to the secondary precipitation of Al3(Sc, Zr) particles. The precipitation strengthening of the Al3(Sc, Zr) phase was the main contributor to the high yield strength of the alloy.

Manufacturing and processing of sheets using a Mg–Al–Ca–Zn–Y alloy for automotive applications

As the transportation industry evolves, so do its needs, creating opportunities for the use of non-standard materials. While electrically powered vehicles (EVs) generally operate at lower temperatures than those with internal combustion engines, operation at elevated temperature is still important for battery cases and motor housings. There, Mg alloy sheets could be used, as they have great potential for lightweighting. Mg–Al–Ca-alloys are particularly suitable, as they form temperature-stable phases, providing advantages compared to classical Mg–Al–Zn alloys.In this work, sheets made of an Mg–Al–Zn–Ca–Y alloy (AZXW3120) were manufactured via hot-rolling. The microstructure and texture in various conditions were analyzed and the mechanical properties were investigated at RT and 150 °C. The Ca additions led to a reduced texture after rolling and allowed for an increase in tensile strength of 15–20 MPa by age hardening. The age-hardenable AZXW3120 sheets showed better formability during cup-drawing (31.4 vs. 27.5 mm) and higher elevated temperature yield strength, of up to 25 MPa, compared to industrially produced AZ31 Mg sheet.

Enhancing ambient and elevated temperature performance of hypoeutectic Al–Ce cast alloys by Al3(Sc,Zr) precipitate

This study explored the consequences of incorporating Sc and Zr into hypoeutectic Al–9Ce cast alloys, specifically investigating their influence on microstructure and mechanical properties. The findings demonstrated the significant reduction in the grain size of the Al–9Ce alloy while successfully maintaining the distinctive shape of the eutectic Al11Ce3 phase through the incorporation of Sc and Zr additions. During aging treatments, Al3(Sc,Zr) coherent precipitates formed both at the interface between the α-Al and Al11Ce3 phases and within the α-Al matrix. Remarkably, this led to optimal hardness achieved within a short duration of 3 h at 350 °C. Peak-aged quaternary Al–9Ce–xSc–yZr alloys showed significantly better tensile strength than the binary Al–Ce alloy at both ambient and elevated temperatures. Overall, the study underscored promising prospects of Al–Ce–Sc–Zr alloys for use in high-temperature applications, as they exhibited enhanced mechanical properties.