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DOE OSTI2025

A critical analysis of U-Pu-Zr phase transitions using calorimetric, microstructural, and phase equilibria data

Metallic fuels consisting primarily of uranium, plutonium, and zirconium (U-Pu-Zr) are a leading material candidate for fast-spectrum nuclear reactors. Early demonstration programs proved the principle of safe and efficient fast reactor operation, however there is still considerable uncertainty regarding the phase equilibria and microstructural evolution across the ternary composition space. Quantitative phase formation and identification measurements are scarce and often incomplete, with studies reporting either phase transition temperatures or phase identification data, but not both from the same specimens. In this study, we critically compared experimental and calculated phase transition data and correlated with the microstructure and phase characterization data of as-cast and annealed U-Pu-Zr alloys. Differential scanning calorimetry (DSC) was used to measure phase transitions in the subsolidus regions (723−948 K) of three ternary U-Pu-Zr alloys with similar plutonium concentrations but various U/Zr ratios. Due to sluggish kinetics and narrow ranges of phase stability, complex peaks required the use of a Frazier-Suzuki peak fitting algorithm to deconvolute and calculate transition peak temperatures and enthalpies. We also identified trends of phase transition behavior by critically comparing our DSC data with previous phase transition measurements as well as historical and calculated phase equilibrium diagrams. In conclusion, this provides a critical approach for benchmarking and assessing the quality of new U-Pu-Zr phase equilibria data prior to its incorporation into nuclear material databases.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2025

Microstructural features and deuterium diffusion in lithium penta-aluminate pellets under He + and D + ion irradiation

Lithium (Li) penta-aluminate (LiAl 5 O 8 ) is investigated as a potential tritium (T) breeding material, with a focus on microstructural response to ion irradiation and deuterium (D) diffusion behavior. Under high-fluence ion irradiation (2 x 10 17 (He + +D + )/cm 2 ) at 773 K, LiAl 5 O 8 exhibits significant disorder on the Li sublattice, as revealed by atomic-resolution scanning transmission electron microscopy, while the Al and O sublattices remain stable, demonstrating strong resistance to structural amorphization. Irradiation induces the formation of platelet-shaped antiphase boundaries (APBs), which may serve as effective D trapping sites. Atom probe tomography suggests the presence of 6 LiD clusters in the mass spectra, though definite conclusions regarding APB composition are hindered by signal overlap and limited data statistics. Time-of-flight secondary ion mass spectrometry reveals that D retention approaches to saturation at 3 x 10 17 (He + +D + )/cm 2 . Isothermal and isochronal annealing studies determine an average diffusivity of 1.6 x 10 -13 at 773 K and an effective activation energy of 0.8 ± 0.1 eV for D migration. Compared to γ-LiAlO 2 , LiAl 5 O 8 demonstrates superior irradiation resistance, minimal Li loss, and enhanced D retention, underscoring its potential as a durable breeder material for T production. In conclusion, these findings provide key insights into the microstructural evolution, defect dynamics, and D retention mechanisms in LiAl 5 O 8 under reactor-relevant conditions.

42 ENGINEERING↗

DOE OSTI2025

Microstructural evolution and hardness changes in ion irradiated nickel-based Haynes 282 superalloy

This study investigated the crucial aspects of thermal and irradiation stability in precipitation hardened Haynes 282 Ni-based superalloy. The Haynes 282 Ni-based alloy was irradiated by 8 MeV Ni 3+ ions to assess its resistance to phase instabilities and mechanical property alterations. The mid-range doses (at a depth of ∼1 µm) were 1 and 10 displacements per atom (dpa) at temperatures of 600°C and 750°C. Nanoindentation tests provided insights into bulk equivalent hardness of the irradiated and pristine regions, while scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) were used to examine the microstructural evolution of irradiation-induced defects and γ′ -Ni 3 (Al, Ti) precipitates and defect structure under irradiation. These precipitates, with an average diameter of 29 nm and a number density of 5 x 10 21 /m 3 , acted as robust dispersion strengthening agents with high radiation point defect sink strength. Remarkably, irradiation did not significantly alter the size or number density of the γ′ precipitates, indicating exceptional thermal stability and radiation resistance of these precipitates at the examined conditions. Radiation-induced dislocation loops were observed at 600°C, albeit without a substantial impact on mechanical properties due to the dominance of γ′ precipitates on the overall alloy strength. The superior stability of γ′ precipitates observed in this study contrasts with several previous research findings on Ni-based alloys that reported poor precipitate stability. Plausible reasons for this difference are discussed. Moreover, this work explicitly outlines a physically grounded approach to ensure accurate microstructure-hardness correlations and clarifies the hardening model by addressing common misapplications of superposition in prior studies.

36 MATERIALS SCIENCE↗

DOE OSTI2026

High energy X-ray characterization of the microstructure of PuGa alloy samples at macroscopic depths and non-ambient conditions

High energy (95 keV) X-rays were utilized to characterize the microstructure of eight PuGa alloy samples at room temperature and during cooling to ∼10 K. The samples had different Ga content (nominally 0-3.4 at.%), age, and history. A ninth sample, similarly characterized with neutron diffraction, was included to extend the Ga range to 7 at.%. The samples span the range from single phase α (monoclinic) to δ (face-centered cubic) PuGa, as well as a two-phase α′/δ sample. The crystallographic textures, phase fractions, lattice parameters and dislocation densities of each sample were evaluated through distinct analysis techniques. The textures of the samples were modest. In each case, the dislocation densities were relatively high, comparable to cold worked metals and metals exposed to similar radiation dose. At room temperature, the lattice parameters determined in the predominantly single-phase samples were larger than expected based on the nominal Ga concentration. The observed lattice thermal expansions of the single-phase δ samples to 10 K are self-consistent across the samples and consistent with previous measurements reported in the literature. Significantly larger thermal lattice strain is observed in the δ phase of the two-phase material due to mechanical constraint from the α′ phase, which has a three times larger thermal expansion and is much harder than the δ phase. In conclusion, the results demonstrate the unique value of high-energy X-rays for relatively routine microstructural characterization of Pu alloy samples.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Phase field simulation of anode microstructure evolution of solid oxide fuel cell through Ni(OH) 2 diffusion

Microstructure evolution in a solid oxide fuel cell anode is strongly affected by operating condition. The detailed mesoscale evolution mechanism under operating condition is still under debate. Here we develop a phase-field model to simulate microstructure evolution through formation and diffusion of gaseous Ni(OH)2. We studied the coarsening kinetics and redistribution of Ni under different steam distributions and compare it to that under pure hydrogen condition. Overall, the results suggest that although the presence of a steady gradient of steam leads to redistribution of Ni, Ni(OH) 2 formation and diffusion do not significantly change the Ni coarsening rate under strictly humid conditions, contrary to commonly reported hypotheses. It is concluded that competing mechanisms other than Ni(OH) 2 diffusion must be responsible for the experimentally observed Ni redistribution and enhanced coarsening under humid conditions.

25 ENERGY STORAGE↗

DOE OSTI2018

Relationship between laser energy input, microstructures and magnetic properties of selective laser melted Fe-6.9%wt Si soft magnets

Highlights: • Effect of laser energy input on magnetic properties of SLM Fe-6.9%wt.Si is described; • Magnetic properties can be described as function of as-built microstructure after stress-relief post-treatment; • Samples with density >99% and strong crystallographic texture along BD have the best magnetic properties; • At very high laser energy, a strong cube texture forms that deteriorates the magnetic properties. - Abstract: Selective Laser Melting (SLM), a powder-bed Additive Manufacturing technology, can be used in combination with high temperature post-annealing to produce high-silicon steel parts characterised by quasi-static magnetic properties comparable to those of commercial electrical steel. However, the role of the as-built microstructure on the magnetic properties is still unexplored. Therefore, in this study the effect of the energy input of the processing laser on the magnetic properties of the material is investigated. The magnetic properties are determined for 4 mm-high rings obtained using three laser energy input values that provide a good compromise in terms of porosity and crack formation. The best magnetic properties are obtained for the rings built using a value of energy input that produces a strong fibrous crystallographic texture, in which one of the crystallographic <001> axes is preferentially aligned along the build direction. Whether the magnetic properties change with sample direction as a result of the crystallographic texture will be the subject of future research.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effect of stored strain energy heterogeneity on microstructure evolution of 90% cold rolled AISI 304L stainless steel during interrupted annealing treatment

Highlights: • Study of usefulness of stored strain energy distribution map of the material for variable temperature range. • Advantage of using stored strain energy distribution map • Variation observed in stored energy between isothermal annealing treatment and interrupted annealing treatment. - Abstract: This research work is an attempt to understand the effect of stored strain energy heterogeneity over macro-scale, induced during interrupted annealing treatment, on the micro structural evolution in a heavily cold rolled AISI 304L austenitic stainless steel. The cold rolled AISI 304L stainless steel (SS) samples were subjected to different annealing treatments. The microstructures obtained after each annealing treatment were characterized using optical and electron microscopy techniques. Further, an attempt was made to estimate the stored strain energy by a novel approach of micro hardness measurement both over small scale (area 3600 μm{sup 2}) and large scale (area ~0.25 mm{sup 2}). The stored strain energy was determined using hardness values. Using these data, spatial stored strain energy distribution contour maps were created. They were, in turn, used to characterize the local softening behavior both at micro and macro-scale levels after each interrupted annealing treatment. The results showed that, interrupted annealing treatment induces increased stored strain energy heterogeneity after each annealing interruptions. Also, it was possible to determine recrystallization kinetics of the material using stored strain energy map, which helps in designing annealing cycles for achieving ultrafine grained microstructure.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Microstructure evolution and a new mechanism of B2 phase on room temperature mechanical properties of Ti-47Al-2Cr-2Nb alloy prepared by hot isostatic pressing

Highlights: • The microstructure evolution of Ti-47Al-2Cr-2Nb alolly was investigated in detail. • The foramtion of B{sub 2} phase can be adjusted in Ti-47Al-2Cr-2Nb alloy. • A new mechanism of B{sub 2} phase on room temperature mechanical properties of Ti-47Al-2Cr-2Nb alloy was proposed. - Abstract: The formation of B{sub 2} phase was adjusted via various hot isostatic pressing processes in Ti-47Al-2Cr-2Nb alloy. The microstructure evolution and a new mechanism of B{sub 2} phase on room temperature mechanical properties was investigated by BSE, EBSD and TEM in detail. The result shows that the formation of B{sub 2} phase leads to Cr element content decrease in γ matrix phase, which results in lattice parameter increase, namely the c/a ratio of γ matrix phase. Finally, at room temperature the mechanical properties of Ti-47Al-2Cr-2Nb alloy deteriorates.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effect of compositional changes on microstructure in additively manufactured aluminum alloy 2139

Highlights: • Volatile elements preferentially vaporize during additive manufacturing. • Vapor losses affect precipitate habit plane in aluminum alloy 2139. • Above 0.2 wt% Mg the precipitate forms on the preferred {111} habit plane. • Higher strength is associated with precipitates on the {111} habit planes. - Abstract: A matrix of nine experiments was conducted on aluminum alloy 2139 samples made by an electron beam directed energy deposition additive manufacturing process to characterize the effect of magnesium vaporization loss on microstructure and properties. The nine-sample matrix included three different magnesium levels deposited onto material at three different temperatures. The goal was to quantify the variability in the deposited material as a function of allowable magnesium content and the local temperature of the substrate or previous layer. The results show that temperature variations in the substrate up to 100 K have no significant effect on the amount of magnesium loss; however, relatively large variations in Mg content, up to a ±0.25 wt%, can significantly affect the microstructure and mechanical properties. This is due to a change in how the precipitate phase forms, which influences the mechanism by which the alloy is strengthened.

36 MATERIALS SCIENCE↗

DOE OSTI2018

On the microstructure characterization of the AA2098-T351 alloy welded by FSW

Highlights: • The microstructural characterization of the AA2098-T351 Al-Cu-Li alloy welded by FSW was carried out. • There was strong correlation between the results of the various techniques. • DSC was an effective technique for characterization of GP zones complementing the microstructural characterization by TEM. - Abstract: The complex structure of the AA2098-T351 alloy welded by friction stir welding (FSW) was investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and microhardness measurements. Thermal modelling process of the FSW process was carried out by soldering thermocouples at distances of 6, 9 and 12 mm from the weld centerline, and thermocouple measurements were used as input data into the model. Finite element software COMSOL v5.2 was used for data analysis. The prevailing phases in the base metal (BM) are T1 (Al{sub 2}CuLi) θ′ (Al{sub 2}Cu), δ′/β′(Al{sub 3}(Li,Zr)) and Ω (Al{sub 2}Cu). In the heat affected zone (HAZ), either in the retreating or advancing sides, θ′ phase was not identified. In the thermomechanical affected zone (TMAZ), T1, δ′/β′, GP zones phase were detected in the retreating side, whereas T1 and Guinier-Preston (GP) zones were not observed in the advancing side. This result supports the asymmetric behavior observed in the microhardness profile of the weld. In the stir zone (SZ), GP zones, T1, δ′/β′ (Al{sub 3}(Li,Zr)) and Ω were identified.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effects of Sr, Ce and P on the microstructure and mechanical properties of rapidly solidified Al7Si alloys

Highlights: • Rapid solidification caused formation of nanoscaled Si particle chains. • Sr or Ce induced the columnar transition zone only at extremely high cooling rate. • Enhancement of hardness is attributed to fine dispersion of eutectic Si, grain refinement and the supersaturation of Si. • Sr or Ce caused further enhancement of hardness, attributing to Si modification. - Abstract: A series of Al7Si based alloys with trace addition of Sr, Ce or P were prepared using melt-spinning at two different high cooling rates, and the microstructure as well as the hardness of the ribbons was comprehensively studied. The results show that Sr or Ce induces the formation of columnar transition zone and modifies the morphology of eutectic Si phase from dispersed particle chains to fine fibers only at extremely high cooling rate. However, P has little effect on the microstructure of either α-Al or eutectic Si. Compared with conventional casting, the Al7Si ribbons exhibit extremely high hardness due to the fine dispersion of eutectic Si, the grain refinement and the supersaturation of Si. The hardness is further enhanced by Sr or Ce addition at extremely high cooling rate, especially for columnar and equiaxed zones, attributing to the modification effect on Si phase.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Investigation of annealing temperature on microstructure and texture of Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel

Highlights: • Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel was investigated. • Shear bands provided recrystallization nucleation sites. • Annealing temperature can affect microstructure and texture. • r-bar increased to a maximum value (1.69) and then decreased to 1.42. - Abstract: The evolution of microstructure and texture of Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel annealed at different temperatures was investigated using a combination of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). EBSD investigations confirm that the in-grain shear bands provide more recrystallization nucleation sites to γ-fiber recrystallization grains with high Taylor factor orientations during cold rolling requiring further annealing for a more homogenous equiaxied grain structure. As the annealing temperatures increase, the grains in center layer are oriented towards {110}∥ND, and the recrystallization grains at 1050 °C are dominated by the uniform and equiaxial γ-fiber grains favourable for the improvement of r-values, while the occurrence of {100} <011> texture detrimental to r-values indicates that an exorbitant annealing temperature can reduce the intensity of γ-fiber textures affecting the formability, accordingly, the average plastic strain ratio of ferritic stainless steel increases sharply up to a maximum value (1.69) and then decreases to a certain value (1.42).

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effect of trace amounts of added Sc on microstructure and mechanical properties of 2055 aluminum alloy

Highlights: • Effect of trace Sc on microstructure and mechanical properties in 2055 Al-alloy was investigated. • T{sub 1} is the main strengthening phase in Sc free and Sc added 2055 alloy at the aging temperature of 175°C and 200°C. • The refinement of T{sub 1} by Sc addition depends on the aging temperature. • Mechanical properties were deteriorated by Sc at the aging temperature of 175°C and improved at 200°C aging treatment. - Abstract: The effects of Sc additions and isothermal aging on the microstructure and mechanical properties of 2055 aluminum alloy have been investigated. The isothermal aging temperatures investigated were 175 °C and 200 °C. Results show that the aging temperature does not affect the type of precipitates in both Sc-free and Sc-added 2055 Al alloys. While remarkable changes in the size and number density of T{sub 1} (Al{sub 2}CuLi) precipitates have been observed. For samples aged at 175 °C for 8 h, the average length of T{sub 1} precipitates was increased from 39.9 nm to 45.6 nm, the number density decreased from 5.77 × 10{sup 22} m{sup −3} to 3.68 × 10{sup 22} m{sup −3} after Sc addition. On the contrary, when samples were aged at 200 °C for 8 h, the length decreased from 59.89 nm to 43.32 nm and number density increased from 2.13 × 10{sup 22} m{sup −3} to 3.00 × 10{sup 22} m{sup −3} by adding trace Sc. Slight deterioration of tensile strength and yield strength with higher ductility was founded at the aging temperature of 175 °C for 8 h due to the larger size and lower number density of T{sub 1} precipitates along with the formation of a W (AlCuSc) phase during the casting or homogenization processes. When aging temperature increased to 200 °C, tensile strength and yield strength were significantly improved by Sc addition without losing ductility. Highly dense fine T{sub 1} precipitates take responsible for the strength improvement, and to some extent it compensated the strength loss caused by the formation of W phase. A “vacancy-prison” mechanism was adopted to explain the effect of Sc additions on the precipitation of T{sub 1} phase as a function of aging temperature.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Microstructure and nanoindentation analysis of Mg-SiC nanocomposite powders synthesized by mechanical milling

Highlights: • Mechanical milling as an effective solution to reach a homogeneous distribution of SiC nanoparticles up to 10 vol% in Mg matrix • No deformation twinning in the nanostructured Mg matrix even after the severe plastic deformation and hard SiC nanoparticles up to 10 vol%. • Significant enhancement of nanohardness and reduced elastic modulus in the milled nanocomposite powders - Abstract: Mixtures of magnesium powder and SiC nanoparticles at various volume fractions were mechanically milled to produce nanocrystalline Mg-SiC nanocomposites. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the microstructure of the milled powders. The microstructural evidences revealed that mechanical milling is a proper method to achieve a uniform distribution of the SiC nanoparticles, even up to 10% in the Mg matrix. Based on the results, higher volume fraction of the SiC nanoparticles raise the value of measured microstrain and reduce the crystallite size of the Mg matrix. The TEM results pointed to the fact that no deformation twinning takes place in the nanostructured Mg matrix even after severe plastic deformation through mechanical milling and the presence of hard SiC nanoparticles up to 10 vol%. The effects of nanoparticle volume fraction on mechanical properties of the milled Mg-SiC nanocomposites were evaluated using nanoindentation tests. The results clearly showed a significant enhancement of nanohardness and reduced elastic modulus in the milled powders compared to that of the reference material namely as-received pure magnesium. It was found that the SiC nanoparticles (even up to 10 vol%), well distributed in the magnesium matrix, remarkably improve the reduced elastic modulus and nanohardness of the nanocomposite powders.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2018

Mechanical property and microstructure evolution of nitrogen-modified Ti-6Al-4V alloy with core-shell structure by hot compression

Highlights: • Core-shell structured Ti-6Al-4 V is composed of α shells and α + β cores. • Nitrogen solution and core-shell structure significantly enhances the strength. • Core-shell structural alloy performs inhomogeneous deformation. - Abstract: Core-shell (CS) structured Ti-6Al-4 V (Ti64) alloy with single α shells and duplex α + β cores was fabricated by powder nitriding and spark plasma sintering. The mechanical property and microstructure evolution of CS-Ti64 alloy was investigated by compression at temperatures of 950–1100 °C and strain rates of 0.001–1 s{sup −1}. The nitrogen-induced solid solution strengthening and the nitrogen-stabilized CS structure significantly enhanced the compressive strength. Microstructure evolution of CS-Ti64, involved inhomogeneous deformation of the core and shell, which was quite different from that of the commercial Ti64. Regions adjacent to shells and central locations of cores suffered large strain and therefore preferentially underwent dynamic recrystallization (DRX). The deformation mechanism of the novel CS-Ti64 alloy was discussed in terms of the α shells, α laths and DRX.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Three-dimensional microstructural analysis of fragmentation behavior of platelet Al3Ti particles in Al-Al3Ti composite deformed by equal-channel angular pressing

Highlights: • Particle distribution in ECAPed Al-Al{sub 3}Ti composite depends on material flow of matrix. • Fragmentation of Al{sub 3}Ti particles by ECAP occurs along twin boundary in the particles. • Al{sub 3}Ti particles in the composite fragment after twin deformation of the particles. - Abstract: The fragmentation of platelet Al{sub 3}Ti particles in an Al-Al{sub 3}Ti composite by equal-channel angular pressing (ECAP) is investigated using three-dimensional (3D) microstructural evaluation and crystallography. The Al-Al{sub 3}Ti composite comprises coarse platelet Al{sub 3}Ti particles in an α-Al matrix. The ECAP of this composite is performed for up to 4 passes under processing routes A, B{sub c}, and C. Route B{sub c} produces the smallest Al{sub 3}Ti particle fragments in comparison with the fragments produced under routes A and C. This is because that route B{sub c} produces the largest number of shearing directions and shearing planes. Platelet Al{sub 3}Ti particle fragments in the specimen deformed by ECAP under route A are homogeneously distributed along the deformation axis. In contrast, in the specimens deformed by four ECAP passes under routes B{sub c} and C, the Al{sub 3}Ti particle fragments are gathered into several groups. The fragment groups have a length similar to the initial length of the platelet Al{sub 3}Ti particles. These spatial distributions of particle fragments can be explained by material flow of α-Al matrix during ECAP. Moreover, from 3D microstructural evaluation and crystallographic analysis of the Al{sub 3}Ti particle fragments, it is found that the Al{sub 3}Ti particles are preferentially fragmented on the twin boundary plane of {112}{sub Al3Ti}. Therefore, it is concluded that fragmentation of a platelet Al{sub 3}Ti particle by ECAP occurs along the twin boundary plane after twin deformation.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Formation of gradient microstructure and mechanical properties of hot-pressed W-20 wt% Cu composites after sliding friction severe deformation

Highlights: • W particles of composites were refined during sliding friction treatment (SFD). • Dislocation, dislocation tangles and boundary clearly exist in deformed W particle. • YS and UTS of SFDed sample are 308.74 MPa and 553.60 MPa owing to the refinement. • Electrical conductivity of SFDed sample decreased from 33 IACS% to 28.5 IACS%. • Fracture mode changing from inter-granular mode to trans-granular. - Abstract: W-based alloys are currently considered promising candidates for high heat flux components in future fusion reactors. In this paper, hot pressed W-20 wt%Cu composites were treated at room temperature using a sliding friction severe deformation (SFD) process, with a moving speed of 0.2 m/s and an applied load of 500 N. Microstructural evolution of composites after the SFD treatment was evaluated and compared with that of the untreated composites. Results showed that there was a gradient structure generated and an obvious refinement in tungsten particles size in the surface layer after the SFD process. The average particle size of tungsten in the SFD treated composites was 2.60 μm, whereas it was 4.5 μm for tungsten in the untreated composites. Fracture surfaces of the composites indicated that the SFD treatment destroyed the W skeleton and changed fracture mode from predominant inter-granular one to trans-granular one due to the decrease in contact area of W-W inter-particles. Yield strength and ultimate tensile strength of composites after the SFD treatment were 308 MPa and 553 MPa, respectively. The treated composites exhibited micro-hardness values with an average reading of about 308 HV. Analysis of the facture microstructures clearly suggested that the tungsten particles in the treated composites are consisted of dislocations and boundaries as well as dislocation tangles. The electrical conductivity of the composites was decreased from 33 IACS% to 28.5 IACS% after the SFD treatment, mainly due to loss or squeezing of copper into the inner surface.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effect of filling materials on the microstructure and properties of hybrid laser welded Al-Mg-Si alloys joints

Highlights: • A serious comparison was made on the hybrid laser welded AA6061-T6 joint with different filling materials. • The microstructure of the welded joint was characterized using EBSD and SEM. • A strength model was successfully built to predict the strength of the hybrid laser welded AA6061-t6 joint. • The study shed new insights on how to select appropriate filling materials when using hybrid laser welding. - Abstract: A serious investigation was conducted to examine the influence of filling materials on the microstructure and properties of hybrid laser welded AA6061-T6 joints. The results of the tensile tests showed that the welded joint with ER4043 filling materials had higher tensile strength than that with ER5356 filling material. Based on the results obtained a strength model was built to predict and explain the enhancement of the yield strength of the hybrid laser welded AA6061-T6 joint with different welding wires. In contrast to the tensile strength, the ER4043 joint showed lower fatigue strength than that of the ER5356 joint due to extensive presence of micropores in fusion zone. Further, the corrosion experiment illustrated that the ER4043 joint had poorer resistance to the corrosive attack under 3.5% NaCl solution. A summary was made on the performance of both welded joints to shed new insights on selecting appropriate filling materials when welding AA6061-T6 by hybrid laser welding method.

36 MATERIALS SCIENCE↗