Alclad Research Articles

Al Clad CF/Al Composite Fabricated by a One-Step Liquid–Solid Infiltration–Extrusion Process: Electrochemical Corrosion and Mechanical Behavior

Al Clad CF/Al Composite Fabricated by a One-Step Liquid–Solid Infiltration–Extrusion Process: Electrochemical Corrosion and Mechanical Behavior

Thermomechanical Performance Assessment of U-Mo Monolithic Fuel Plates With Zircaloy Cladding

Abstract Performance of two distinct fuel systems, U-7Mo fuel in Zircaloy (Zry-4) cladding and U-10Mo fuel in aluminum (Al6061-O) cladding was studied. First, a mini plate with Zry-4 cladding from a previous irradiation experiment was evaluated via finite element analysis (FEA). By using the same plate geometry and irradiation conditions, another plate consisting of U-10Mo fuel and Al6061-O cladding was simulated. The results were then comparatively evaluated to explore the feasibility of employing Zry-4 as an alternative cladding. Simulations indicated the Zircaloy cladding plate would operate roughly 50 °C hotter as compared with the Al alloy cladding plate. Larger deformations in the thickness direction for the plate with Zry cladding were noted. It was observed that the postfabrication stresses in the fuel would be relieved quickly in the reactor, regardless of cladding type. Although the fuel stresses would still develop at reactor shutdown, the fuel would be stress-free during the entire irradiation period for both cladding types. At shutdown, the plate with Zry cladding would have higher stresses due to higher operating temperatures. Similarly, the stresses after shutdown are higher in the foil core for the plates with Zry cladding. The Al cladding plate would have higher plastic strains as compared with the Zry cladding plate. The Zry cladding plate is significantly stiffer, causing higher stresses in the fuel zone and at the interface. Overall, employing Zry as an alternate cladding is not expected to produce a more favorable thermomechanical performance as compared to the performance of an Al alloy cladding plate.

High-value utilization of intermetallic Cu9Al4 as an additive to improve the hydrogen storage performance of magnesium

As a product of in the preparation of Cu–Al clad composites, intermetallic Cu9Al4 greatly affects the mechanical properties of the composites due to its high hardness and poor plasticity, which limits its application. Here, Cu9Al4 is used as an additive to improve the hydrogen storage performance of Mg. Thereby, the Cu9Al4 was introduced into Mg to prepare the Mg‒x wt.% Cu9Al4 composites (x = 0, 5, 10, 15, 20 and 25) by high-energy ball milling. The microstructure and phase composition of the composites under different states were analyzed. The hydrogen absorption and desorption kinetics and thermodynamics of the composites at different temperatures are investigated. Compared with pure Mg, the addition of Cu9Al4 can significantly improve the dehydrogenation kinetics of Mg. With the increase of Cu9Al4 content, the hydrogen desorption rate gradually increased. When the Cu9Al4 content was 20 wt.%, the dehydrogenation activation energy calculated according to JMAK kinetic model and Arrhenius equation was the lowest (96.84 kJ mol−1), and it had the best hydrogen desorption kinetics. Especially, the phase transition of the first hydrogen absorption process for the Mg‒20 wt.% Cu9Al4 was studied in detail. The results show that the Cu9Al4 phase first transforms into (Cu1.3Al0.7)Mg during the first hydrogenation, and then Mg reacts with H2 to generate MgH2. In the subsequent dehydrogenation and re-hydrogenation cycles, the (Cu1.3Al0.7)Mg is stable and does not change.

Numerical Simulation and Experimental Prediction of the Cladding Layer Based on the Response Surface Method

To study the surface morphology of laser cladding, Workbench simulated the influence of laser power and scanning speed on the width and height of the cladding layer numerically, as well as the temperature field change and residual stress distribution of the cladding layer. The simulation results reveal that the melting height and width of the cladding layer are inversely proportional to the scanning speed. When the scanning speed is from V = 3 mm/s to V = 5 mm/s, the Al cladding layer’s melting width and melting height are reduced by 15.59% and 20.8%, respectively. A positive correlation exists between the melting height and width of the cladding layer and the laser power. When the laser power changes from P = 23 w to P = 27 w, the welding width and height of the A1 cladding layer increase by 6.55% and 55.56%, respectively. The melting height and width of the second cladding layer are generally higher than those of the bottom cladding layer. The pre-experiment screening process parameters ranges are laser power P (23 w–27 w) and scanning speed (3 mm/s–8 mm/s). Based on the Minitab response surface central composite method, the most notable influence on the melting height and width is revealed to be the powder-feeding rate and laser power, respectively. The response surface analysis method establishes the regression prediction models of melting width and height. The predicted value of melting width was 95.68%, and the predicted value of melting height was 82.26%. The results show that the values of cladding width and height are within the 95% prediction interval, proving that the regression model is correct.

Prolonged fatigue life in aluminum clad steel by electropulsing treatment: Retardation of interface-microcrack formation

The prolonged fatigue life of aluminum clad steel (Al clad steel, ACS) using electropulsing treatment is systematically investigated by characterizing the microstructural change at different fatigue cycles. The microstructural changes associated with fatigue damage evolution show that cracks are prone to initiate at Al grains of the interface and propagate toward the Al side in the fatigue test due to a preferred accumulation of geometrically necessary dislocations (GNDs) in the soft Al grains near the interface. The electropulsing treatment with a subsecond duration is proved to be efficient in healing the fatigue damage and significantly prolonging the fatigue life of the ACS. The increased fatigue life by electropulsing treatment is attributed to the diminished density of piled GNDs and the retardation of microcrack formation at the interface. The present study elucidates the failure mechanism of ACS and proves that electropulsing treatment is an efficient method to prolong the fatigue life of laminated metal composites by healing the accumulated damage during the fatigue test.

Microstructure and phase constitution at the interface of double-sided electron beam welded Cu/Al clad metal sheet

The microstructure of the interfa ce zone is the most important factor to determine the properties of the Cu/Al clad metal sheet joint. The composition distribution and phase constitution at the interface of the double-sided electron beam welding (DSEBW) joint of 6.5 mm thick Cu (1.5 mm)/Al (5 mm) clad metal sheet were revealed by means of technologies of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was confirmed that there formed a distinct transition zone with a length of about 5.8 mm at the interface, and it consisted of a thin layer of IMC and a large area eutectic structures. Moreover, the thickness distribution of IMC layer in the center and edges of the interface zone was nonuniform, and gradually decreased from the center (7.5 μm) to the edges (1.5 μm and 2.6 μm) by means of SEM and EBSD. Furthermore, the eutectic structure performed the superior laminar, and the grey IMC dispersed in Al-rich dendrites inside the eutectic structure. In addition, the interface zone mainly consisted of two slices, including Cu/IMC interface (Interfaces I and III) and IMC/eutectic structure interface (Interfaces II and IV). For interfaces I and III, this IMC was Al2Cu, and there was no other IMCs between Cu and Al2Cu IMC by means of TEM; For interfaces II and IV, the eutectic structure was composed of Al2Cu and α-Al, while there was also no other IMCs between Al2Cu IMC and (Al2Cu + α-Al) eutectic structure. In short, the microstructure characterizations at the whole interface of the DSEBW joint were Al2Cu IMC and (Al2Cu + α-Al) eutectic structure.

Gas Bubble Evolution in Polycrystalline UMo Fuels Under Elastic-Plastic Deformation: A Phase-Field Model With Crystal-Plasticity

In monolithic UMo fuels, the interaction between the Al cladding and large gas bubble volumetric swelling causes both elastic-plastic and creep deformation. In this work, a phase-field model of gas bubble evolution in polycrystalline UMo under elastic-plastic deformation was developed for studying the dynamic interaction between evolving gas bubble/voids and deformation. A crystal plasticity model, which assumes that the plastic strain rate is proportional to resolved shear stresses of dislocation slip systems on their slip planes, was used to describe plastic deformation in polycrystalline UMo. Xe diffusion and gas bubble evolution are driven by the minimization of chemical and deformation energies in the phase-field model, while evolving gas bubble structure was used to update the mechanical properties in the crystal plasticity model. With the developed model, we simulated the effect of gas bubble structures (different volume fractions and internal gas pressures) on stress-strain curves and the effect of local stresses on gas bubble evolution. The results show that 1) the effective Young’s modulus and yield stress decrease with the increase of gas bubble volume fraction; 2) the hardening coefficient increases with the increase of gas bubble volume fraction, especially for gas bubbles with higher internal pressure; and 3) the pressure dependence of Xe thermodynamic and kinetic properties in addition to the local stress state determine gas bubble growth or shrinkage. The simulated results can serve as a guide to improve material property models for macroscale fuel performance modeling.

Effects of Annealing and Deformation on Sagging Resistance of a Hot‐Rolled, Four‐Layered Al Alloy Clad Sheet

Multilayer brazeable aluminum alloy sheet is prone to collapse during high‐temperature brazing process. The sagging resistance of the aluminum composite sheet needs to be further improved for quality control. Effects of annealing and rate of reduction on sagging resistance, microstructure, and Si diffusion of a hot‐rolled, four‐layered Al clad sheet (4343/3003/6111/3003) were investigated by means of a sagging device, OM, SEM, and TEM. Results showed that once annealed at 360°C, the sagging distance was increased from 3 to 15.7 mm as the reduction rate changed from 10% to 40%. By increasing annealing temperature to 410°C, those were changed from 3.1 to 20.8 mm accordingly. At 360°C/40% and 410°C/40%, specimens exhibited weak sagging resistance, whereas fine recrystallized grains were formed in the core promoting Si penetration along grain boundaries. While the specimens were treated at 360°C/10% and 410°C/10%, better sagging resistance was observed due to the formation of coarse recrystallized grains that can suppress erosion of Si. At the same reduction rate, the sagging resistance was higher for the sample annealed at a lower temperature as more precipitates appeared in the core (at 360°C), thus leading to an increase in strength.

Fabrication of aluminum–magnesium clad composites by continuous extrusion

Abstract Poor corrosion resistance of Mg alloys extremely limits their industrial applications. Al/Mg clad composites using Al alloy as a protective layer are expected to be an effective approach to combine good corrosion resistance and high specific strength. In this study, novel Al clad Mg composites were developed by continuously extruding 6063 Al alloy tube and AZ31 Mg alloy rod with and without preheating of Mg alloy. The Al/Mg interfacial diffusion, microstructure, texture, and flexural properties of the continuously extruded composites were investigated experimentally. The extruded composites exhibited good metallurgical bonding between Al shell and Mg core even without preheating of Mg alloy, and their fine-grained microstructure contributes to a significant enhancement in ultimate flexural strength (UFS) to 452 MPa. Preheating of Mg alloy caused complete dynamic recrystallization (DRX) of both Al shell and Mg core and modified (0001) texture of the Mg alloy, which leads to a significant improvement in the bendability of the Al/Mg composite.

Methodology for ultrasonic inspection of dispersion type U–Mo fuel plates

Nuclear fuel based on uranium-molybdenum alloys (U–Mo) showed a promising performance under irradiation tests, except for an undesirable interaction between the U–Mo fuel particles and the aluminum matrix. This development requires new methods and evaluation criteria for inspection of this fuel. Non-destructive analysis techniques, such as Ultrasonic Test (UT), can play a key role in the characterization and in-pile monitoring of test fuel plates, in particular, for the anisotropic fuel core.This paper proposes the establishment of a relationship between attenuation and transmission effects for U–Mo fuel plates with different uranium loads, based on mathematical processing of UT signals. For this purpose, the Chilean Nuclear Energy Commission (CCHEN) manufactured a set of 8 dispersion type test plates, with uranium loads from 1 to 8 gU/cm3. The U–Mo fuel plates were evaluated in transmission mode with a Panametrics PR 5800 pulser-receiver ultrasonic system, using frequencies of 20 and 25 MHz. The data set collected for each plate was processed using the Fourier Function transform of the data function in MATLAB®. The obtained results showed that the attenuation coefficient of the ultrasonic waves increased linearly as a function of the uranium load. From 12.3 dB/mm for 1 gU/cm3 to 74.2 dB/mm, for 8 gU/cm3. The transmission percentage of the signal reduces linearly as a function of uranium load and the grain boundaries present in the Al cladding, decreasing from 66.7% for 1 gU/cm3 to 9.1% for 8 gU/cm3. In conclusion, the uranium load and the metal forming processes strongly affects the response of the fuel plates subjected to UT scanning. These results established an acceptance criterion for fuel plates based on this response, and the transformations experienced by the fissile U–Mo material.

Microstructural Analysis of 1100 Al Clad 5083 Al by Friction Stir Processing

Microstructural Analysis of 1100 Al Clad 5083 Al by Friction Stir Processing

Effects of porous fuel structure on the irradiation-induced thermo-mechanical coupling behavior in monolithic fuel plates

A UMo/Al monolithic fuel plate is composed of UMo fuel meat and Al cladding. These fuel plates with a high uranium density have a promising prospect to be used in advanced research and test reactors. Under the neutron irradiation environments, nuclear fissions occur to result in heat generation in the fuel meat; accumulation of fission-induced solid and gaseous products will lead to irradiation swelling; irradiation creep of UMo will affect the mechanical interactions between the fuel meat and the cladding. Especially, intragranular and intergranular gas bubbles will make the fuel meat evolve into a porous structure, and the fuel porosity and pore pressure will change continuously with the irradiation time. As a result, a complex irradiation-induced multi-scale thermo-mechanical coupling behavior needs to be simulated for optimal design and safety evaluation of UMo/Al monolithic fuel plates. In this study, a theoretical model for fuel porosity evolution is developed, based on a fission gas swelling model with the grain recrystallization, the resolution of intergranular gas atoms and the dependence of hydrostatic pressure involved. Moreover, the computation method of microscopic interfacial normal stress is established, with consideration of fuel porosity and pore pressure. The evolution model of fuel porosity is introduced into three-dimensional finite element simulation of the irradiation-induced multi-scale thermo-mechanical coupling behavior, which correlates the current thermal conductivity of UMo fuel with the fuel temperature and porosity. The distribution and evolution disciplines of thermo-mechanical variables in the fuel plate are obtained at different irradiation time. In addition, the effects of fuel porosity on the temperature, the main deformation and microscopic interfacial normal stresses are investigated. Simultaneously, the effects of surface heat transfer coefficient on the thermo-mechanical behavior are analyzed. The research results indicate that the porous fuel structure and fission-gas induced pore pressure become the main fracture mechanisms of monolithic fuel plates.

Examining the Oxide Disruption Mechanism of a Nickel PVD Coating on Anodized Aluminum Braze Sheets

The reaction sequence between a sputtered nickel coating and surface-oxidized Al clad braze sheet was investigated using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS on the surface showed that both the nickel and alumina layers remained roughly intact with some interactions occurring locally, confirmed by optical and SEM characterizations. The predominant phase found upon nickel entering the Al-Si melt was Al3Ni, and it was proposed that this formation led to the disruption of the alumina layer mechanically, primarily due to mechanical disruption of the oxide by the intermetallic and its bonding with the alumina layer. These interactions of aluminum and nickel were proposed to occur at defects inherent in the alumina layer either during fabrication or as a result of fracture caused by thermal stresses while floating on the molten clad layer.

Effect of annealing temperature on microstructure and bond strength of cast-rolling Cu–Al clad plates

Effect of different annealing temperatures on evolution of microstructure in copper-aluminum clad plates prepared by cast-rolling were investigated using scanning and transmission electrical microscopy, and x-ray diffraction. Peeling tests were conducted to characterize the bond strength of prepared clad plates. Results showed that with the increase in annealing temperature, the bond strength of the 8 mm thick copper-aluminum clad plates first increased and then decreased. When the annealing temperature was 250 °C–300 °C for 3 h, CuAl2 was formed at the interface, promoting atomic diffusion and improving the bond strength. However, when the annealing temperature was 300 °C–400 °C for 3 h, providing enough energy for a new Cu9Al4 intermetallic phase formed at the interface, and the thickness of the interface layer increased from about 1 μm to 11 μm, while the bond strength decreased from 42 ± 0.8 N·mm−1 to 12 ± 1 N·mm−1. The fracture pattern of the clad plates extensible to brittle with the annealing temperatures from 300 °C to 450 °C for 3 h. According to the experimental results, the optimal annealing temperature for copper-aluminum clad plates prepared by cast-rolling is 300 °C for 3 h.

Cladding of aluminum alloy 6061-T6 to mild steel by an electromagnetic tube bulging process: finite element modeling

Bimetal tubes have useful applications in various industries where service conditions demand more different requirements in the tube core than its outside surface. The recent use of electromagnetic forces to deform or join metallic workpieces at high speeds has undergone rapid growth for materials processing. However, to date, no sufficient systematic understanding of the underlying principles of a subsequent high-speed electromagnetic tube bulging process to manufacture bimetal tubes has been gained. In this work, magnetic pulse cladding of Al/Fe clad bimetal tubes was analyzed by finite element modeling (FEM) using ANSYS software. The validity of FEM analyses was first confirmed by experiments in terms of the deformed shape. Second, the effect of cladding parameters (such as axial feeding being the dominant factor in the multi-step process) on the bulging and thinning behavior of the Al clad tube was presented in detail. Both the numerical simulation and experimental results show that no more than 70% of the bulging-coil length is an appropriate amount for the feeding length to prevent defects from being introduced by non-uniform deformation in the transition zone of the Al clad tube. The distributions of the magnetic flux line, magnetic force, and plastic strain in different cladding steps were then analyzed. It was concluded that during the multi-step cladding process, there was an uneven distribution of the magnetic field force along the transition zone. Consequently, inharmonious plastic deformation behavior occurs, which results in a limited acceleration of the transition zone to a certain impact velocity.

Mechanical properties of irradiated U[sbnd]Mo alloy fuel

This paper presents results of studies characterizing the mechanical properties of irradiated U10Mo fuel in support of low-enriched fuel conversion of several United States high-performance research reactors (USHPRR), specifically the monolithic base fuel qualification. Specimens were tested from ten test fuel plates irradiated at the Advanced Test Reactor (ATR) from the RERTR-12 and AFIP-6 Mk. II irradiation campaigns. Tests were conducted at Idaho National Laboratory (INL) in the Hot Fuel Examination Facility (HFEF) inert atmosphere Main Cell. The monolithic fuel plates consist of a U10Mo fuel foil meat covered with a Zr diffusion barrier layer fabricated by co-rolling, and clad in 6061 Al using a hot isostatic press (HIP) bonding process. Initial unirradiated specimens exhibited nominal (fresh) fuel meat thickness ranging from 0.25 mm to 0.64 mm, and irradiated (as tested) fuel plate average burnup ranged from approximately 0.36 × 1021 to 6.2 × 1021 fissions/cm3. After sectioning individual specimens from the fuel plates, the 6061 Al cladding was removed by dissolution in concentrated NaOH. Pre-dissolution measurement of width and post-dissolution measurement of thickness were conducted on test specimens to facilitate accurate analysis of bend test results. The final thickness values varied from 0.3 to 0.8 mm. Four-point bend testing was conducted on the HFEF Remote Load Frame (RLF) using custom-designed test fixtures and calibrated force and displacement sensors. All specimens exhibited dominantly elastic behavior and failed in a brittle manner. Analysis of test results showed decreasing elastic modulus and bending failure strength with increasing fission density. The trend of modulus decrease intersected with unirradiated modulus at zero fission density. The trend of decreasing bending strength with increased fission density is apparent, but has significantly higher uncertainty levels than the modulus results over the fission density range evaluated. A linear trend fit of the calculated bend strengths versus fission density does not coincide with unirradiated tensile strength, which is significantly higher. Porosities measured on the test specimen material are used with several model equations to predict irradiated modulus values. Over the range of available porosity information, comparison to the experimental modulus values are favorable. Other factors and their potential influence on modulus and strength calculations are discussed.

Interfacial characteristic of multi-pass caliber-rolled Mg/Al compound castings

Herein, magnesium/aluminum (Mg/Al) composite rods were prepared by compound casting and multi-pass warm caliber rolling, and the effect of caliber rolling on the evolution of the interfacial microstructure and mechanical properties of the Mg/Al compound castings was investigated. The results reveal a uniform interface, which can be divided into three layers consisting of Al3Mg2, Al12Mg17 and (Al12Mg17 + Mg) eutectic structure, was formed during the compound casting. Afterwards, the brittle reaction layer fragmented during the rolling process, and was effectively eliminated after 12 passes. Meanwhile, the fresh Al and Mg bases squeezed out and bonded together under the rolling force. The interface formed after the final rolling process had no visible intermetallic compounds. Further, an inhomogeneous deformation in the Mg and Al bases was observed during the rolling process. Initially, the Al clad layer accommodated a larger proportion of the plastic deformation. With increasing number of passes, however, the strain in the Mg core layer increased and, after 12 passes, the deformation of both layers tended to be equivalent. The strength of the Mg/Al composite rod increased gradually and the ultimate tensile stress reached a value of 247 MPa after 12 passes.

Thermo-mechanical behavior simulation coupled with the hydrostatic-pressure-dependent grain-scale fission gas swelling calculation for a monolithic UMo fuel plate under heterogeneous neutron irradiation

Abstract Monolithic UMo fuels have a higher uranium density than previously developed fuels. They have become the most promising fuels to be used in high-flux research and test reactors after the US Office of Material Management and Minimization Reactor Conversion Program (formerly Reduced Enrichment Research and Test Reactor (RERTR) program). In this study, a computational method is established to couple the macro-scale irradiation-induced thermo-mechanical behavior simulation with the hydrostatic-pressure-dependent fission gas swelling calculation in the UMo grain. The stress update algorithms and consistent stiffness moduli are respectively presented for UMo fuel, in which both the hydrostatic-pressure-dependent irradiation swelling and deviatoric-stress-directed irradiation creep are taken into account. Accordingly, the user subroutines to define the thermo-mechanical non-homogeneous constitutive relations for the UMo fuel meat and Al cladding are developed and validated. The in-pile behavior in a monolithic UMo fuel plate under a location-dependent irradiation condition is calculated and discussed.

3D reconstructions of irradiated U[sbnd]Mo fuel to understand breaching effects in ZrN diffusion barriers

To understand interaction layer behavior in UMo fuel kernels coated with physical vapor deposition (PVD) ZrN barriers, two cubes of irradiated fuel were serial sectioned and imaged in 50 and 200 nm increments using a focused ion beam (FIB) instrument. Locally, the fuel underwent a burnup of 52% U235 or a fission density of 4.0 × 1021 fissions/cm3. 3D reconstructions were created from the serial sectioned images. 3D reconstructions revealed the morphology of multiple locations where UMo/Al interaction layer formed between the Al matrix and the UMo fuel. These locations are associated with breaches in the ZrN barrier and not from diffusion of Al through the ZrN barrier. When not compromised, the ZrN barrier successfully impedes UMo fuel interaction with Al cladding. The ZrN barrier has decreased from a nominal pre-irradiated thickness of 1.16 μm to a thickness of 0.69 μm. A ZrN-rich phase adjacent to the ZrN barrier was observed on the Al matrix side of the coating. This phase is likely the original ZrN barrier and Al matrix that decomposed with increasing burnup as a result of fission recoil induced mixing. Nominally, the thickness of the irradiated ZrN barrier and the ZrN-rich Al matrix is 1.36 μm.

Interface Characterization and Performances of a Novel Pure Al Clad Al Alloy Wire

Based on the principle of skin effect, a pure Al clad Al alloy wire is designed to break the mutually exclusive relation between strength and electrical conductivity. Actually, bimetallic composite wires offer the ability to blend the desired properties of various metals into a single wire, for example, combining the high‐conductivity of pure Al (outer layer) and the high‐strength of Al alloy (core). Thus, a novel method is adopted to prepare a pure Al clad Al alloy wire (ACAW) and the metallurgical bonding between pure Al and Al alloy is achieved by compressing the Al alloy cylinder into a hollow pure Al cylinder followed by a series of processes including forging, rolling, and cold‐drawing. A perfect interface is obtained as the fine grains are found across the interface. Furthermore, a linear rule of mixtures is applied to calculate the performance of ACAW as compared with the measured performance of ACAW. The measured strength of ACAW is the same as the calculated strength. Interestingly, the measured electrical conductivity of ACAW (58.17%IACS) is higher than the calculated electrical conductivity (57.60%IACS). Consequently, ACAW is an effective approach for combining the high‐conductivity of pure Al and the high‐strength of Al alloy.