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1. In situ investigation into temperature evolution and heat generation during additive friction stir deposition: A comparative study of Cu and Al-Mg-Si

   https://doi.org/doi.org/10.1016/j.addma.2020.101386  

   Garcia, David; Hartley, W. Douglas; Rauch, Hunter A.; Griffiths, R. Joey; Wang, Rongxuan; Kong, Zhenyu J.; Zhu, Yunhui; Yu, Hang Z. (August 2020, Additive manufacturing)

   null (Ed.)

   Additive friction stir deposition is an emerging solid-state additive manufacturing technology that enables site-specific build-up of high-quality metals with fine, equiaxed microstructures and excellent mechanical properties. By incorporating proper machining, it has the potential to produce large-scale, complex 3D geometries. Still early in its development, a thorough understanding of the thermal process fundamentals, including temperature evolution and heat generation mechanisms, has not been established. Here, we aim to bridge this gap through in situmonitoring of the thermal field and material flow behavior using complementary infrared imaging, thermocouple measurement, and optical imaging. Two materials challenging to print via beam-based additive technologies, Cu and Al-Mg-Si, are investigated. During additive friction stir deposition of both materials, we find similar trends of thermal features (e.g., the trends of peak temperature , exposure time, and cooling rate) with respect to the processing conditions (e.g., the tool rotation rate and in-plane velocity ). However, there is a salient, quantitative difference between Cu and Al-Mg-Si; exhibits a power law relationship with / in Cu but with / in Al-Mg-Si. We correlate this difference to the distinct interfacial contact states that are observed through in situ material flow characterization. In Cu, the interfacial contact between the material and tool head is characterized by a full slipping condition, so interfacial friction is the dominant heat generation mechanism. In Al-Mg-Si, the interfacial contact is characterized by a partial slipping/sticking condition, so both interfacial friction and plastic energy dissipation contribute significantly to the heat generation. 

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2. Morphological and microstructural investigation of the non-planar interface formed in solid-state metal additive manufacturing by additive friction stir deposition

   https://doi.org/10.1016/j.addma.2020.101293  

   Perry, Mackenzie E.J.; Griffith, R. Joey; Garcia, David' Sietins; Zhu, Yunhui; Yu, Hang Z. (October 2020, Additive manufacturing)

   null (Ed.)

   Additive friction stir deposition (AFSD) is an emerging solid-state metal additive manufacturing technology renowned for strong interface adhesion and isotropic mechanical properties. This is postulated to result from the material flow phenomena near the interface, but experimental corroboration has remained absent. Here, we seek to understand the interface formed in AFSD via morphological and microstructural investigation, wherein the non-planar interfacial morphology is characterized on the track-scale (centimeter scale) using X-ray computed tomography and the material deformation history is explored by microstructure mapping at the interfacial regions. X-ray computed tomography reveals unique 3D features at the interface with significant macroscopic material mixing. In the out-of-plane direction, the deposited material inserts below the initial substrate surface in the feed-rod zone, while the substrate surface surges upwards in the tool protrusion-affected zone. Complex 3D structures like fins and serrations form on the advancing side, leading to structural interlocking; on the retreating side, the interface manifests as a smooth sloped surface. Microstructure mapping reveals a uniform thermomechanical history for the deposited material, which develops a homogeneous, almost fully recrystallized microstructure. The substrate surface develops partially recrystallized microstructures that are location-dependent; more intra-granular orientation gradients are found in the regions further away from the centerline of the deposition track. From these observations, we discuss the mechanisms for interfacial material flow and interface morphology formation during AFSD. 

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3. Hardness Distribution of Al2050 Parts Fabricated Using Additive Friction Stir Deposition

   https://doi.org/10.3390/ma16031278  

   Ghadimi, Hamed; Ding, Huan; Emanet, Selami; Talachian, Mojtaba; Cox, Chase; Eller, Michael; Guo, Shengmin (February 2023, Materials)

   The solid-state additive friction stir deposition (AFSD) process is a layer-by-layer metal 3D-printing technology. In this study, AFSD is used to fabricate Al–Cu–Li 2050 alloy parts. The hardness values for various regions of the as-deposited built parts are measured, and the results are contrasted with those of the feedstock material. The as-fabricated Al2050 parts are found to have a unique hardness distribution due to the location-specific variations in the processing temperature profile. The XRD results indicate the presence of the secondary phases in the deposited parts, and EDS mapping confirms the formation of detectable alloying particles in the as-deposited Al2050 matrix. The AFSD thermal–mechanical process causes the unique hardness distribution and the reduced microhardness level in the AFSD components, in contrast to those of the feedstock material. 

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4. The influence of additive friction stir deposition process on mechanical properties, corrosion resistance, and electrical conductivity of Al5086-H32 alloy

   https://doi.org/10.1007/s40964-025-01072-x  

   Zavari, Saeid; Bagheri, Ehsan; Ding, Huan; Adibi, Noushin; Eller, Michael; Cox, Chase; Guo, Shengmin (April 2025, Progress in Additive Manufacturing)

   Abstract Additive friction stir deposition (AFSD) is a novel additive manufacturing technique that enables the fabrication of components in the solid state. Given the benefits of AFSD, understanding the behavior of various feedstock materials after undergoing the AFSD process is crucial for optimizing their performance in structural applications. This study aims to evaluate the effects of AFSD on an Al–Mg alloy, Al5086, comparing it to its initial H32 condition to assess the changes in mechanical properties, microstructure, corrosion resistance, microhardness, and electrical conductivity. Tensile testing showed a 23% reduction in yield strength for as-deposited samples, while ultimate tensile strength remained comparable to the feedstock. Ductility improved significantly, with elongation to failure increasing by 77%, attributed to grain refinement and dynamic recovery. Microhardness decreased by 16% in lower layers due to thermal exposure, but electrical conductivity remained stable, indicating minimal solute atom redistribution. The Nitric Acid Mass Loss Test (NAMLT) revealed a 245% increase in corrosion rate for the AFSD material, linked to the higher density of grain boundaries acting as pathways for corrosion. These findings highlight AFSD’s potential for improving ductility and formability. However, they underscore the need for optimization to reduce corrosion susceptibility and address mechanical strength trade-offs. Future work should focus on fine-tuning process parameters or implementing post-treatment methods to enhance corrosion and mechanical performance. 

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5. The Effects of Layer Thickness on the Mechanical Properties of Additive Friction Stir Deposition-Fabricated Aluminum Alloy 6061 Parts

   https://doi.org/10.3390/met14010101  

   Ghadimi, Hamed; Talachian, Mojtaba; Ding, Huan; Emanet, Selami; Guo, Shengmin (January 2024, Metals)

   Solid-state additive friction stir deposition (AFSD) is a thermomechanical-based additive manufacturing technique. For this study, AFSD was utilized to produce aluminum alloy 6061 (AA6061) blocks with varying layer thicknesses (1 mm, 2 mm, and 3 mm). The mechanical properties were assessed through uniaxial tensile tests and Vickers microhardness measurement, and statistical analysis was employed to investigate differences among data groups. The results revealed that the deposition layer thickness influences tensile properties in the building (Z) direction, while the properties in the X and Y directions showed minor differences across the three AFSD blocks. Furthermore, variations in tensile properties were observed depending on the sample orientation in the AFSD blocks and its depth-wise position in the part in the building direction. The microhardness values decreased non-linearly along the building direction, spread across the width of the part’s cross-section, and highlighted that the deposition layer thickness significantly affects this property. The 1 mm block exhibited lower average microhardness values than the 2 mm and 3 mm blocks. The temperature histories and dynamic heat treatment are influenced by the deposition layer thickness and depend on the location of the point being studied in the part, resulting in variations in the microstructure and mechanical properties along the building direction and across the part’s width. 

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