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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

High-speed friction stir butt welding of 25.4 mm thick 7175-T79 aluminum alloy

This presents the first experimental demonstration of friction stir butt welding of 25.4 mm thick high-strength, precipitate-strengthened 7XXX aluminum alloy at a welding speed above 500 mm/min and penetration depth greater than 10 mm. Tool pin threads that terminate away from the shoulder region, helped mitigate nearby stress concentration during tool traversing, enabling a higher welding speed while avoiding pin fracture near shoulder. Two kinds of welds—one-sided with full penetration of the plate thickness and double-sided with partial penetration of the plate thickness—were conducted. Significant grain refinement (grain size 1.3 ± 0.8 µm) was evident at the junction of double-sided friction stir welding (FSW) compared to other regions of weld-nugget or base material. Cross-weld tensile testing with digital image correlation revealed high local strains at the junction of double-sided FSW before macro-yield. This strain concentration impeded the typical early necking on advancing/retreating sides of FSW joints, improving the yield strength of as-welded double-sided FSW by 20–24% over slow- to medium-speed one-sided FSW. In conclusion, the joint efficiency of as-welded, double-sided high-speed FSW was about 76% with respect to the base material’s ultimate tensile strength.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Stress characterization for friction-stir-welded electric vehicle battery trays with application of neutron diffraction

The battery tray is an essential component that protects and controls battery-cell temperatures in electric and plug-in hybrid vehicles. The functional stress limit of the battery tray heavily depends on the residual stress acquired from the manufacturing process. Consequently, exceeding the stress limit of the battery tray during operation could compromise the battery-cell banks and may risk the vehicle's safety. Hence, understanding residual stress formation is vital for design and safety concerns. Here, in the current study, AA 6061-plates were friction stir welded to an A365 high-pressure die-cast battery tray to create sealed coolant channels in the battery tray. However, this multi-material lap friction stir weld introduces residual stress into the battery tray, resulting in distortion. This distortion was mitigated using burnishing or coining operations, though straightening the battery tray had initially unknown effects on the residual stress. Therefore, neutron diffraction was utilized to characterize residual stresses after straightening. The results indicate that the friction stir welding (FSW) operation generated residual stresses exceeding the yield strength of the material, consequently deforming the battery tray by ±3 mm from the pre-weld geometry. The burnishing operation reduced the residual stresses below the material's yield strength while restoring the tray to within ±0.75 mm of the pre-weld geometry. Similarly, the coining operation restored the battery tray to within ±0.75 mm of the pre-weld geometry, however, increasing the number of locations where the residual stress exceeds the yield strength of the material.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Impact of Backing Plate and Thermal Boundary Conditions for High-Speed Friction Stir Welding of 25-mm Thick Aluminum Alloy 7175-T79

Here this study demonstrates high-speed (150 mm/min) single pass friction stir butt joining of 25 mm thick aluminum alloy 7175-T79. To understand the impact of quenching and cooling rate on process responses, joint strength, and grain size distributions across the weld thickness, we performed a series of friction stir welding (FSW) trials in air and with a trailing water spray using steel and composite backing plates (BP). Welds made in air and trailing water spray exhibit significantly different hardness distributions across the nugget, heat affected zone (HAZ), and HAZ minimum hardness as evidenced by detailed microhardness mapping. The effect of trailing water spray (TWS) on joint efficiency overshadows the influence of BP composition due to the vastly different contribution to quenching. TWS also resulted in a multifaceted effect on FSW such as lowering processing temperature, increasing X and Z forces while lowering Y force, and narrow heat affecting zone. Finally, digital image correlation (DIC)-based fracture mode analysis and grain size measurements correlate with the hardness distribution.

42 ENGINEERING↗
DOE OSTI2023

Microstructural, Corrosion, and Mechanical Characterization of Friction Stir Welded Al 6022-to-ZEK100 Mg Joints

Friction stir welded (FSW) aluminum–magnesium lightweight vehicle joints have gained significant interest due to their high strength-to-weight ratio. In this work, the corrosion resistance of this material is analyzed through electrochemical tests, which include open circuit potential (OCP) inspection and potentiodynamic polarization (PD) scanning. Weight loss measurements tested the corrosion rate of the FSW weld through cyclic corrosion testing (CCT) according to the standard SAEJ 2334. Mechanical properties were also investigated, including lap-shear strength, micro- and nano-hardness mapping, and true stress–strain curves as a function of local processing history. The electrochemical results indicate that the center weld zone’s corrosion property stays between the two base alloys. Indentation-based testing demonstrated that the weld zone behaves differently from base alloys. Lap shear strength surprisingly did not drop much even after eight weeks of cyclic corrosion tests, indicating that the joint did not allow any ingress of the electrolyte.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Stress interference in multilayer additive friction stir deposition of AA6061 aluminum

Due to the multilayer deposition nature of metal additive manufacturing processes, each layer being printed experiences the state of thermokinetic and thermomechanical stress that in turn interfere with the state of thermokinetics and thermomechanical stress of subsequently deposited layers. Especially, this multilayer interference significantly affects the resultant properties of the component fabricated using solid-state additive friction stir deposition due to evolution of asymmetric state of planar stress. Due to the lack of comprehensive and suitable in situ diagnosis technique, the complex interference of inter- and multi-layer stresses during additive friction stir deposition was studied in an integrated approach of numerical simulation of fluidic state and experimental probing of stress influenced ultrasonic elastography. The uni-directional and bi-directional layer deposition configurations adopted during additive friction stir deposition result in the generation of constructive and destructive interference of the interlayer stress and hence, asymmetric and symmetric dynamic elasticity distribution respectively within the subsequent layers. With subsequent deposition of additional layers, the odd and even numbers of deposited layers generate asymmetric and nearly symmetric dynamic elasticity distributions.

Yang, Teng↗
DOE OSTI2026

Quantitative characterization of gradient microstructures: A study on friction stir spot processing of pure cobalt

Heterogeneous microstructures in polycrystalline metals can enhance the strength and ductility, outperforming homogeneous structures of similar composition. This study investigates deformed cobalt via friction stir spot processing with varying dwell times to uncover the effects of plastic deformation and heat generation on the formation of morphological, phase, and grain boundary character gradients. A new approach to quantify the morphological gradients in materials, which describes grain morphology in terms of density followed by parametric regression, enables direct quantification of processing depth and gradient sharpness. Results show that longer processing times increase the steepness of morphological gradients and reduce the deformation depth for friction stir spot processing with low plunge depths and high tool rotational speeds. The amount of retained FCC is increased in the shorter processing conditions, primarily due to refined grain size, increased defect content, and reduced heat generation. Crystallographic texture analysis of the HCP phase indicated a dominant B-fiber described by (0001) ∥ shear plane normal in the extreme processing conditions and the formation of a P-fiber, shear direction ∥ ⟨11$\bar2$0⟩ for intermediate dwell times. The texture of the FCC phase for low processing times was a C texture {100}⟨011⟩ where longer processing times were dominated by a [001] fiber texture with a main {110}⟨100⟩ orientation and emergence of a slight [111] fiber in the longest processing condition. The approaches outlined in this work give insight into quantifying gradients and improve the understanding of highly deformed cobalt.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Creep Behavior of Friction Stir Processed Haynes 282

Haynes 282 is a nickel-based superalloy designed for use in hot sections of turbines for aircraft and power generation. In these applications, elevated temperature creep performance is critical. To that end, creep behavior of friction stir processed material was carried out to investigate the high-temperature performance of this alloy. Friction stir processing of Haynes 282 was successfully completed, and the processed region was found to be defect-free. Various mechanical property characterization approaches were carried out in post-heat treated condition. Transverse tensile samples repeatedly failed in the base metal indicating 100% joint efficiency. Creep property evaluation was completed at 760 °C and at various stress levels. The creep-rupture lifetime of the processed material was similar to the base metal. Detailed electron microscopy analysis of the failed sample was carried out to understand the microstructural evolution in various locations of the sample during creep.

creep↗
DOE OSTI2022

Towards underwater additive manufacturing via additive friction stir deposition

Given the challenges in feed material supply and quality control, metal additive manufacturing has rarely been implemented in austere environments, especially underwater. This paper explores the underwater operation potential of an emerging solid-state additive technology: additive friction stir deposition, wherein material feeding and bonding are enabled by mechanical forces with minimal influences from water. It is demonstrated that additive friction stir deposition of 304 stainless steel can be successfully performed with the print head and substrate immersed in water. High temperature is reached in the deposition zone (>60% melting temperature); the material deposition behavior is similar to that in typical open-air operation. The as-deposited material is fully-dense, having fewer annealing twins and a substantially smaller grain size than the feed material (4.98 μm vs. 31.44 μm ). Such microstructural changes stem from dynamic recrystallization caused by the large strain and high temperature introduced during deposition. In addition to grain refinement, small equiaxed dispersoids (~2–3 μm or less) are formed and evenly distributed in the austenite steel matrix. Rich in Cr, Mn, and O, these particles likely result from the reaction between the elements in stainless steel and water at elevated temperatures.

16 TIDAL AND WAVE POWER↗
DOE OSTI2021

Process Robustness of Friction Stir Dovetailing of AA7099 to Steel with In Situ AA6061 Interlayer Linking

Rolled homogeneous armor (RHA) steel was joined to aluminum alloy AA7099-T7451 with an interlayer of AA6061-T651 by single-pass friction stir dovetailing (FSD). The evolution of the AA7099/AA6061 and AA6061/steel interfacial microstructures and mechanical properties of the joints were examined. The AA6061 interlayer prevented Zn migration from the AA7099 to the steel during FSD and inhibited formation of brittle, Zn-rich, Fe-Al intermetallic compounds within the joint. The flow of the dissimilar aluminum alloys at the interface was controlled with a partially threaded friction stir welding pin and a dovetail geometric configuration optimized in previous work. The process robustness was explored to establish parameter windows by elucidating parametric effects on the relationship between process conditions and the joint’s microstructure and mechanical properties. Ranges of process forge force (50–70 kN) and interface temperature (475°C–515°C) consistently yielded joints with adequate performance. The load-carrying capacity in lap shear tensile tests was 2025 ? 100 N/mm.

Friction Stir Dovetailing, FSW, AA7099, AA6061, Ro↗
DOE OSTI2020

Manufacturing of magnesium/aluminum bimetallic ring components by friction stir assisted simultaneous forging and solid-state joining

Here, a bimetallic ring component is forged by a friction stir assisted forging (FS-forging). A cylindrical bimetallic blank, magnesium AZ31 cylinder (Mg core) tightly fitted inside an aluminum 6061-T6 tube (Al skin), is used. In the FS-forging, the frictional heat and stirring of rotating tool forge the blank into a desired shape, while simultaneously generate a solid-state joint between the Mg core and the Al skin, without additional external heating, as confirmed by the microstructural analysis and mechanical tests. The microstructural analysis also shows that the characteristics of the solid-state joint can be different depending on the process parameters.

42 ENGINEERING↗
DOE OSTI2023

Comprehensive Characterization of Helium-Induced Degradation of the Friction Stir Weld on Neutron-Irradiated 304L Stainless Steel

The report describes new experimental results on the mechanical performance of the friction stir welds made on neutron-irradiated 304L stainless steel with helium. The report focuses on helium-related issues (e.g., the helium-induced degradation in the welded joint), aiming at the need to repair irradiated components of nuclear power plants. The friction stir welds analyzed here were previously produced at the US Department of Energy’s Oak Ridge National Laboratory, and initial characterization work was performed, mostly addressing the microstructure and if macroscopic cracks and helium bubbles present. The present work attempts to perform a more comprehensive study to assess mechanical performance (i.e., microhardness distribution, tensile properties, tensile deformation behaviors, and fractography analysis).

36 MATERIALS SCIENCE↗
DOE OSTI2023

Defect‐Free Sound Insulator Using Single Metal‐Based Friction Stir Process Array

Metals are excellent conductors for phonon transportation such as vibration, sound, and heat. Generally, metal sound insulators require multimaterial structure or defects and unimetal sound insulators are challenging. Therefore, a design of a defect-free sound insulator made by single alloys with multiple friction stir processes (FSPs) is proposed. Periodic friction stir processing can induce superlattice-like local mechanical properties’ modifications. By experimental acoustic characterization, it is observed that FSP can introduce clear acoustic–elastic property contrast on an aluminum plate by the presence of stir zone and heat-affected zones. In numerical simulations, the signature FSP-induced property profile is periodically and parallelly arranged on a long aluminum plate. The transmission gap frequencies are present on the frequency spectrum with the sound propagation direction perpendicular to the FSP paths. Disorder offsets on FSP periodicity are further introduced. Anderson localization is found on a resonance frequency, which provides −11 dB sound reduction by an exponential decay. Due to the finite design length, the slight disorder can also enhance sound insulation in the periodic transmission gap frequency. In conclusion, with analysis and comparison with different configurations, the best performance in the models can achieve −30 dB sound insulation in the 350 mm-long aluminum alloy plate with 14 parallel FSPs.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High performance aluminum-air flow batteries through double-face architecture and laser-modified and friction-stir processed 3D anode

Aluminum-air batteries (AAB) are regarded as one of the most promising beyond-lithium high-energy-density storage candidates. Here, this paper introduces a three-dimensional (3D) Al 7075 anode enabled by femtosecond laser and friction-stir process which, along with a special double-face anode architecture provides world-class performance. Electrochemical characterizations prove that the corrosion resistance of the modified 3D Al 7075 FSP anode was enhanced, and electrochemically active surface area (ECSA) was increased compared with that of normal Al 7075 anode. Friction-stir processing reduced the mean grain size from 30 μm to 3 μm. The discharge performance of 3D Al 7075 FSP anode is shown to be quite stable, and the average values of energy density are significantly increased from 2256 mWh g –1 to 2941 mWh g –1 at 100 mA cm –2 . In a double-face flowing Al-air battery system, the 3D Al 7075 FSP anode exhibited significantly better electrocatalytic performance (discharge voltage of 0.76 V at 400 mA cm –2 , and power density of 337.8 mW cm –2 ) than that of a commercial Al 7075 anode.

25 ENERGY STORAGE↗
DOE OSTI2021

Microstructure and Mechanical Performance of the Friction Stir Welds Made on Neutron-Irradiated Steel with Helium

This report describes new experimental results on the microstructure and mechanical performance of the friction stir welds made on neutron-irradiated steel with helium. The report focuses on helium-related issues, specifically, helium-induced degradation in the welded joint, aiming to repair irradiated components of nuclear power plants (NPPs). The friction stir welds analyzed here were produced at Oak Ridge National Laboratory previously, and limited characterization work was performed, mostly addressing the presence or absence of macroscopic cracks. The present work attempts to perform a more comprehensive study to assess microstructure conditions, grain size, plastic strain gradients, the morphology of the helium-induced damage, and deformation behavior.

42 ENGINEERING↗
DOE OSTI2021

Microstructure based modeling of friction stir welded joint of dissimilar metals using crystal plasticity

We report the friction stir welding (FSW) process shows promising results in joining dissimilar metals which are otherwise almost impossible to join using traditional welding techniques. Being a new technique, the deformation and the failure mechanism of the joints made by the FSW process needs to be investigated. In this work, a joint between AZ31 Mg alloy and DP590 steel is modeled using phenomenological crystal plasticity formulation on the mesoscale in the form of a representative volume element (RVE). The interface of the two materials is modeled using a cohesive zone model. A parametric study has been performed to understand the effect of grain size and interface fracture toughness as well as strength on the mechanical performance of the joint. It was found that the grain size of AZ31 Mg alloy, as well as DP590 steel, has little effect on the overall joint performance. On the other hand, interface fracture toughness and strength have a significant impact on the mechanical properties of the joint

36 MATERIALS SCIENCE↗
DOE OSTI2026

Towards High-Speed friction stir welding of 25 mm Thick AA2139-T8: tool innovation and process development

Joining thick plates (≥ 12 mm) of aluminum (Al) alloys is challenging due to high tool forces, uneven material flow, and non-uniform heat distribution through the material’s thickness. Recent advancements in tool design and welding parameters for friction stir welding (FSW) in thick plates butt joining have encountered a developmental plateau, highlighting the need for innovative approaches to overcome existing limitations. Here, this study focuses on the systematic development of single-pass and double-pass FSW processes for high-strength aluminum alloy AA2139-T8, to improve joint efficiency and enable high-speed welding capabilities. Experimental evidence is presented for a novel tool design with opposing pin threads, enabling high-speed (178 mm/min) single-pass friction stir butt welding of 25 mm thick AA2139-T8. A series of FSW trials was conducted both in air and with a trailing water spray, using steel backing plates (BPs) to investigate the impact of quenching and cooling rates on process response and joint performance. A joint efficiency of 83% was attained using the novel tool features and effectively controlling process forces and thermal boundary conditions.

AA2139-T8↗
DOE OSTI2021

Microstructure and mechanical properties of friction stir welded Haynes 282

Advanced ultrasupercritical (A-USC) steam plants are designed to operate at high temperatures and pressures due to the necessity for higher operational efficiency. The extreme operating conditions of A-USC requires the deployment of precipitation strengthened Ni-base alloys that exhibit elevated temperature strength and good fabricability. Fusion welding of precipitation strengthened nickel alloys lead to solidification cracking in fusion zone and/or liquation cracking in heat affected zone. Therefore, an alternative non-melting welding technique is a necessity to efficiently join nickel alloys. In the current study, friction stir welding, a solid state joining technique was implemented on a precipitation strengthened nickel-based superalloy, Haynes 282. Detailed microstructural and mechanical properties characterization was carried out. The processed region exhibited wrought, fine-grained microstructure, absence of weld defects such as voids and cracks and absence of elemental segregation. Both hardness and cross-weld tensile tests demonstrated that the weld region was stronger than the base material. And the cross-weld tensile samples failed in the base material. Based on joint efficiency analysis, friction stir welded Haynes 282 outperformed fusion welds.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of tool design and pass strategy on defect elimination and uniform, enhanced tensile properties of friction stir processed high-pressure die-cast A380 alloy

This work reports implementation of friction stir processing (FSP) to locally modify microstructure and create a defect-free processing zone with the aid of different tool designs and altering the passing strategy for two different process parameter combinations. Here, FSP is applied on high pressure die-cast (HPDC) A380 alloy, a widely used Al-Si alloy fabricated in the die casting sector for automotive and aerospace applications. However, the presence of gas and shrinkage porosity, brittle needle-shaped Fe-containing ß-FeSiAl 5 intermetallic compounds, Al-dendrites, coarse and acicular silicon particles, and large second-phase particulates have a detrimental influence on the uniformity of tensile properties across the thickness direction of an HPDC plate. FSP is able to eliminate porosity, refine microstructure and improve tensile properties. An FSP tool design and a passing strategy are identified for the best microstructure consolidation and uniform enhanced tensile properties. This study noted the importance of tool features such as scroll design and flats on tool pin and multiple pass orientation strategy to find best combination of defect-free refined microstructure and uniform tensile strength and ductility across the processing zone of HPDC Al alloys.

36 MATERIALS SCIENCE↗