Solid-state Additive Manufacturing Research Articles

Investigation on in-situ tensile behaviors of 6061 aluminum alloy fabricated by wire additive friction stir deposition

Rod based additive friction stir deposition (R-AFSD) offers unique advantages for the integrated manufacturing of aluminum alloy near-net-shape large parts. However, the deposition process often faces issues like thick ends of raw material rods and difficulties in continuous feeding. In this study, wire based additive friction stir deposition (W-AFSD) was used for the solid state deposition of 3mm diameter 6061 aluminum alloy wire. The microstructure evolution and mechanical properties of the deposit along the build direction were systematically characterized, clarifying the recrystallization mechanism and isotropy of the mechanical properties. In-situ scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were used to study the deformation behavior of the deposit during in situ tensile testing, revealing a cooperative deformation mechanism involving grain rotation and intragranular slip. Results show that during in-situ tensile testing, the average rotation angle of five selected grains is 6.90°. Additionally, deposits with numerous grain boundaries due to recrystallization can hinder dislocation movement and pin the slip system within the grains during tensile testing. Due to the synergy of these mechanisms, the yield strengths of the longitudinal and transverse samples of the deposit are 183MPa and 190MPa, respectively, much higher than previously reported values. This article introduces a new solid state additive manufacturing method, offering new insights for efficient, high-strength continuous additive manufacturing of aluminum alloys and their deformation mechanisms.

Solid State Additive Manufacturing of Thermoset Composites.

Softening and subsequent deformation are significant challenges in additive manufacturing of thermal-curable thermosets. This study proposes an approach to address these issues, involving the preparation of thermosetting composite powders with distinct curing temperatures, the utilization of cold spray additive manufacturing (CSAM) for sample fabrication, and the implementation of stepwise curing for each component. To validate the feasibility of this approach, two single-component thermosetting powders P1 and P2 and their composite powder C were subjected to CSAM and stepwise curing. From the sample morphology observation and deposition/curing mechanism investigation based on thermomechanical analysis and differential scanning calorimetry, it is found that severe plastic deformation occurs during the CSAM process, accompanied by heat generation, leading to local melting to promote a good bond at the contact surface of the particles and form small pores. During the progressive curing, the samples printed using C demonstrate superior deformation resistance compared with those using P1 and P2, and the curing time is reduced from 16.7 h to 1.5 h, due to the sequential curing reactions of P1 and P2 components in composite C, allowing the uncured P2 and cured P1 to alternately remain solid for providing structural support and minimizing deformation.

Understanding process parameter-induced variability for tailoring precipitation behavior, grain structure, and mechanical properties of Al-Mg-Si-Mn alloy during solid-state additive manufacturing

Additive friction stir deposition (AFSD), a solid-state additive manufacturing technique, has excellent industrial application potential, particularly for Al alloys. However, in-depth process parameter-microstructure-property correlations are lacking, especially regarding precipitation behavior. In this work, AFSD of Al-Mg-Si-Mn alloy with various process parameter combinations was performed to understand the variation (by ∼ 70 %) in the nano/microhardness, concerning the precipitation behavior. The low nano/microhardness sample exhibited dissolution of the β” strengthening phase. However, higher nano/microhardness samples showed varying microstructural features with high dislocation density owing to fine-scale pre-β” precipitation and another sample possessed inhomogeneous β” phase distribution and β’ precipitation at the grain boundaries, thus exhibiting reprecipitation during AFSD. The variation in the grain structure was such that the high nano/microhardness samples exhibited large, elongated grains (∼11 to 13 µm) and low recrystallization fractions (∼16 –18 %) suggesting a predominantly non-recrystallized microstructure. Conversely, the lowest nano/microhardness sample exhibited the smallest grain size (∼5 µm) and, a higher recrystallization fraction (∼42 %). These findings demonstrate extensive variation in the precipitation behavior, grain structure, and mechanical properties due to the process parameters. Future applications can leverage this knowledge to tailor the microstructure and mechanical properties based on the identified process parameter combinations.

Cold spray - a solid-state additive manufacturing technology

Abstract Cold spray is a solid-state powder deposition technique and has evolved into an additive manufacturing process. Unlike conventional additive manufacturing technologies that rely on melting and solidification, cold spray additive manufacturing (CSAM) forms components at low temperatures at a relatively high build rate. This article introduces the technical principles, process parameters and typical microstructure of cold spray, as well as its applications in the fabrication of 3D components and damaged component repair. Current issues faced in cold spray research and future development directions in CSAM are also discussed.

Evolution of Material Properties and Residual Stress with Increasing Number of Passes in Aluminium Structure Printed via Additive Friction Stir Deposition.

Additive friction stir deposition (AFSD) is an emerging solid-state additive manufacturing process with a high deposition rate. Being a non-fusion additive manufacturing (AM) process, it significantly eliminates problems related to melting such as cracking or high residual stresses. Therefore, it is possible to process reactive materials or high-strength alloys with high susceptibility to cracking. Although the residual stresses are lower in this process than with the other AM processes, depending on the deposition path, geometry, and boundary conditions, residual stresses may lead to undesired deformations and deteriorate the dimensional accuracy. Thermal cycling during layer deposition, which also depends on the geometry of the manufactured component, is expected to affect mechanical properties. To this day, the influence of the deposit geometry on the residual stresses and mechanical properties is not well understood, which presents a barrier for industry uptake of this process for large-scale part manufacturing. In this study, a stepped structure with 4, 7, and 10 passes manufactured via AFSD is used to investigate changes in microstructure, residual stress, and mechanical property as a function of the number of passes. The microstructure and defects are assessed using scanning electron microscopy and electron backscatter diffraction. Hardness maps for each step are created. The residual stress distributions at the centreline of each step are acquired via non-destructive neutron diffraction. The valuable insights presented here are essential for the successful utilisation of AFSD in industrial applications.

Additive friction stir deposition of Al 6061-B4C composites: Process parameters, microstructure and property correlation

Al 6061-B4C metal matrix composites were fabricated using a novel solid state additive manufacturing technique of additive friction stir deposition (AFSD). Incorporation of B4C particles into the deposit was achieved by employing hollow Al 6061 feed stock filled with B4C powder and three different AFSD tool rotational speeds (200, 300 and 400 rpm). Fabricated deposits exhibited remarkable metallurgical bonding across the substrate/deposit interface and interlayer interfaces for all tool rotational speeds, indicating a wider fabrication window. A physics based pseudo-thermo mechanical model was employed to evaluate the thermo-kinetic conditions experienced by the depositing material to correlate with the microstructural observations. Deposited layers exhibited refinement of grains to ∼10 μm from the corresponding coarse grain structure of feedstock (136 μm). The regions near the B4C particles were observed to have finer grains (<2 μm) signifying particle stimulated nucleation. Although considerable loss in the tensile properties (60 % drop in yield strength) was observed in the AFSD deposits due to the associated dissolution of β’’ precipitates, subsequent heat treatment restored the tensile properties to the level of as received material (∼290 MPa). The thermo-kinetic conditions (temperature in excess of 500 °C and strain rates in excess of 250 s−1) experienced by the builds under higher AFSD tool rotational speeds (300 and 400 rpm) appeared to result in refinement of Al–Fe–Si based secondary intermetallic precipitates/dispersoids leading to the observed higher stability of their microstructure during the subsequent post AFSD heat treatment. Samples AFSD fabricated with a lower tool rotational speed of 200 rpm, however, exhibited significant grain growth on account of relatively larger secondary precipitates/dispersoids.

Suppressing anisotropy in additive manufacturing by shear crystallographic texture development during multi-layer friction stir deposition

The solid-state additive manufacturing (AM) approach based on a strategy of sheet lamination (SL) using friction stir deposition/friction surfacing, and was investigated for multi-layer metal deposition in the present study. This resulted in synthesis of fully dense parts with a homogeneous and thermally stable fine-grain microstructure with isotropic properties by avoiding solidification-related defects and exploiting dynamic recrystallized shear crystallographic texture component. A non-heat-treatable AA5083 aluminum-magnesium alloy exhibiting serration yielding behavior was used for friction stir additive manufacturing (FSAM) solid-state deposition using a rotational speed of 1000 rpm with two working windows for the consumable rod feed rate in the range of 35–45 mm/min and a traverse speed in the field of 300–400 mm/min. The microstructural features and mechanical properties were assessed across different sections of the solid-state deposited AA5083 alloy structure to verify a pore-free structure with homogeneous and isotropic behavior. Metallography revealed the formation of uniform and refined equiaxed grains derived from continuous dynamic recrystallization (CDRX) with an average size of ∼4 μm over the entire region of the deposited wall through outstanding layers diffused adhesion. Mechanical testing of the multi-layer structure indicates isotropic tensile properties along the building direction (BD) and transverse direction, due to the shear crystallographic texture formed by thermo-mechanical processing during additive deposition process. An excellent combination of ultimate tensile strength (of 370 MPa) and elongation to fracture at ∼33 % was achieved enhanced by serration yielding tensile flow behavior due to solute element/dislocation interactions during plastic straining.

Machine learning in solid state additive manufacturing: state-of-the-art and future perspectives

Machine learning in solid state additive manufacturing: state-of-the-art and future perspectives

The feasibility of resistance seam welding as an additive manufacturing technology for Al 1060

Resistance seam welding additive manufacturing (RSAM) is a new solid-state additive manufacturing technique that utilizes pulsed current and pressure to welding powders layer by layer. In this study, Al1060 powder was employed as the raw material to prepare R0 and R10 samples through RSAM technology and subsequent repeated welding processes, respectively. The results showed that, compared to R0, the grain size of the R10 sample decreased from 34.3 μm to 8.7 μm, and the dislocation density increased from 4.355 × 1014 to 9.436 × 1014 m−2. Additionally, due to the additional heat and pressure from repeated welding, the porosity decreased from 0.998% to 0.017%, the ultimate tensile strength and elongation improved from 63.5 ± 0.5 MPa and 4.5 ± 0.1% in R0 to 93.3 ± 0.5 MPa and 34.3 ± 0.1% in R10. The improvement in mechanical properties is primarily due to the combined effects of grain refinement, dislocation strengthening, and pore self-healing. This study introduces a feasible new approach for additive manufacturing of aluminum alloys and other materials that is difficult to be additively manufactured by other methods.

Hybrid additive manufacturing of aluminum matrix composites with improved mechanical properties compared to extruded counterparts

Great difficulties existed in fabricating large components of SiC particles reinforced aluminum matrix composites with excellent mechanical properties using existing manufacturing procedures. This study demonstrated that the challenges can be addressed by developing a hybrid solid-state additive manufacturing method. The influence of the deposition procedures and the post-processing heat treatment on the microstructure and mechanical properties of the SiC particles reinforced 2009 aluminum ally matrix composites (SiCp/2009Al composites) was systematically investigated using advanced technologies such as spherical aberration corrected transmission electron microscope, atom probe tomography, etc. The results showed that the SiCp/2009Al composites produced by the hybrid solid-state additive manufacturing exhibited enhanced tensile properties and improved isotropy in mechanical properties compared to the extruded feedstock of SiCp/2009Al composites. This was attributed to the formation of dense metal with uniformly distributed SiC particles, high-density of Cu–Mg co-clusters, refined grains and SiC particles, low deformation texture, tightly bonded SiCp/2009Al interface, and sound interfacial bonding between deposited layers.

AFSD-Nets: A Physics-Informed Machine Learning Model for Predicting the Temperature Evolution During Additive Friction Stir Deposition

Abstract This study models the temperature evolution during additive friction stir deposition (AFSD) using machine learning. AFSD is a solid-state additive manufacturing technology that deposits metal using plastic flow without melting. However, the ability to predict its performance using the underlying physics is in the early stage. A physics-informed machine learning approach, AFSD-Nets, is presented here to predict temperature profiles based on the combined effects of heat generation and heat transfer. The proposed AFSD-Nets includes a set of customized neural network approximators, which are used to model the coupled temperature evolution for the tool and build during multi-layer material deposition. Experiments are designed and performed using 7075 aluminum feedstock deposited on a substrate of the same material for 30 layers. A comparison of predictions and measurements shows that the proposed AFSD-Nets approach can accurately describe and predict the temperature evolution during the AFSD process.

Heat-balance control of friction rolling additive manufacturing based on combination of plasma preheating and instant water cooling

Friction rolling additive manufacturing (FRAM) is a solid-state additive manufacturing technology that plasticizes the feed and deposits a material using frictional heat generated by the tool head. The thermal efficiency of FRAM, which depends only on friction to generate heat, is low, and the thermal-accumulation effect of the deposition process must be addressed. An FRAM heat-balance-control method that combines plasma-arc preheating and instant water cooling (PC-FRAM) is devised in this study, and a temperature field featuring rapidly increasing and decreasing temperature is constructed around the tool head. Additionally, 2195-T87 Al-Li alloy is used as the feed material, and the effects of heating and cooling rates on the microstructure and mechanical properties are investigated. The results show that water cooling significantly improves heat accumulation during the deposition process. The cooling rate increases by 11.7 times, and the high-temperature residence time decreases by more than 50 %. The grain size of the PC-FRAM sample is the smallest, i.e., 3.77±1.03 μm, its dislocation density is the highest, and the number density of precipitates is the highest, the size of precipitates is the smallest, which shows the best precipitation-strengthening effect. The hardness test results are consistent with the precipitation distribution. The ultimate tensile strength, yield strength and elongation of the PC-FRAM samples are the highest (351±15.6 MPa, 251.3 ± 15.8 MPa and 16.25 %±1.25 %, respectively) among the samples investigated. The preheating and water-cooling-assisted deposition simultaneously increases the tensile strength and elongation of the deposited samples. The combination of preheating and instant cooling improves the deposition efficiency of FRAM and weakens the thermal-softening effect.

Effect of feeding material shape on microstructures and mechanical properties in friction rolling additive manufacturing

Friction rolling additive manufacturing (FRAM) is a solid-state additive manufacturing method capable of accommodating a wide range of material forms. However, there is a lack of comprehensive research on the optimal feedstock form. Thus, this study investigated the influence of feedstock shape on material formation, microstructure, and mechanical properties. The results revealed that irrespective of whether a strip or wire was used, the plasticized material flowed through a thin plastic flow channel (approximately 112 μm) between the tool head and the feedstock. Wire feedstock resulted in greater deformation and more significant grain refinement than strip feedstock, with grain refinements of 95 % and 81 %, respectively. Additionally, gaps between multiple wires were filled with plasticized material, forming a dense and defect-free mixing zone. Moreover, the tensile performances of the deposited samples obtained from wire and strip feedstocks exhibited no significant differences, measuring 143.9 MPa and 144.5 MPa, respectively. Numerical simulations were employed to elucidate the underlying mechanism of the temperature field and material flow behavior when strips and wires were used as feed materials. The findings of this study are anticipated to serve as a reference for selecting feedstock forms for FRAM.

Microstructure and Mechanical Behavior Comparison between Cast and Additive Friction Stir-Deposited High-Entropy Alloy Al0.35CoCrFeNi.

High-entropy alloys (HEAs) are new alloy systems that leverage solid solution strengthening to develop high-strength structural materials. However, HEAs are typically cast alloys, which may suffer from large as-cast grains and entrapped porosity, allowing for opportunities to further refine the microstructure in a non-melting near-net shape solid-state additive manufacturing process, additive friction stir deposition (AFSD). The present research compares the microstructure and mechanical behavior of the as-deposited AFSD Al0.35CoCrFeNi to the cast heat-treated properties to assess its viability for structural applications for the first time. Scanning electron microscopy (SEM) revealed the development of fine particles along the layer interfaces of the deposit. Quasi-static and intermediate-rate compression testing of the deposited material revealed a significant strain-rate sensitivity with a difference in yield strength of ~400 MPa. Overall, the AFSD process greatly reduced the grain size for the Al0.35CoCrFeNi alloy and approximately doubled the strength at both quasi-static and intermediate strain rates.

Comparative sustainability assessment of powder bed fusion and solid-state additive manufacturing processes: The case of direct metal laser sintering versus additive friction stir deposition

This work aims to conduct a comparative sustainability assessment between two promising additive manufacturing methods: additive friction stir deposition (AFSD) and direct metal laser sintering (DMLS). The comprehensive evaluation in this assessment accounts for environmental, economic, and social dimensions, incorporating life cycle global warming potential, water footprint, and energy demand of the materials used. Key performance indicators are also used to rank these processes, employing various Multi-Criteria Decision-Making techniques. The findings of the study reveal that AFSD exhibits superior sustainability when compared to DMLS, with AFSD achieving a sustainability score of 69%, while DMLS lags behind at 31%. Notably, the sensitivity analysis elucidates that the variance in build volume between the two methods exerts the most substantial influence on the sustainability score, accounting for a 4.2% difference. Additionally, production speed plays a pivotal role in determining sustainability outcomes. On the other hand, mechanical properties have the least impact on the overall results. This outcome can be attributed to the marginal disparities in ultimate tensile strength, yield strength, and hardness exhibited by both AFSD and DMLS.

Solid-state additive manufacturing of dispersion strengthened aluminum with graphene nanoplatelets

Additive friction stir deposition (AFSD) successfully deposited graphene nanoplatelets (GNP) at concentrations of 0.0, 0.4, 0.8, and 1.1 wt% with AA6061 powders. Each concentration of GNP-AA6061 consisted of four consecutive layer-by-layer depositions on AA6061-T6 substrate. The hardness of the deposits varied from 48 Hv to 55 Hv, where a critical concentration of GNP appears to be required for a notable increase in hardness to occur (>0.8 wt%). This hardness response scaled with the tensile responses, with the highest yield and ultimate strengths belonging to the 1.1 wt% GNP of 104 ± 6 MPa and 195 ± 0.9 MPa respectively. The changes in strength are linked to grain refinement with increasing GNP content as well as a higher amount of dispersion strengthening from the GNPs within the grains. Unlike prior research on AFSD where consolidated AA6061 feedstock bars with GNPs are used, the hardness and strength is higher with this powder mixture approach.

DEPOSITION QUALITY OPTIMIZATION OF ADDITIVE FRICTION STIR DEPOSITED ALUMINIUM ALLOY USING UNSUPERVISED MACHINE LEARNING

Additive friction stir deposition (AFSD) is a promising solid-state additive manufacturing technology, but achieving continuous high deposition quality remains challenging due to complex process-structure connections. This study investigates unsupervised machine learning algorithms for mapping process parameters to deposition outcomes without requiring extensive labelled data. On experimental deposition data, algorithms including hierarchical clustering, k-means, spectral clustering, Gaussian mixtures, autoencoders, and self-organizing maps are used. The algorithms find intrinsic patterns and groupings in the multi- factor process data in an unbiased manner. With a silhouette score of 0.7618, k-means clustering performed the best, showing cohesive data clustering. Visualizations like dendrograms and trained maps shed light on the links between process parameters and deposition quality. The cluster analysis identifies process conditions that result in poor deposition quality. This highlights the ability of unsupervised approaches to capture deposition process patterns based solely on data with no prior system knowledge. This data-driven strategy has the potential to significantly improve AFSD process optimization and control, with implications for boosting industrial adoption. The unsupervised learning framework lays the groundwork for using process data to improve the quality and productivity of advanced manufacturing procedures.

Thermo-mechanical process variables driven microstructure evolution during additive friction stir deposition of IN625

Additive friction stir deposition is an innovative technique for solid-state additive manufacturing involving complex thermo-mechanical processes such as frictional heating, plastic deformation, and viscoplastic material flow, which repeats layer by layer during material deposition. The present study is an attempt to understand the relationship between the complex thermo-mechanical process attributes and the resultant microstructure in additive friction stir deposition of IN625. The estimation of thermo-mechanical process attributes, primarily temperature and strain rate during multi-layer deposition was based on the already established thermo-pseudo-mechanical description of friction stir based processes. The complex thermo-mechanical interaction associated with multi-layer material deformation, deposition, and flash formation can be attributed to variations in the average deposition temperature and the strain rate. Microstructural examination of the additive friction stir deposited sample was performed using electron backscatter diffraction. As a result of the additive friction stir deposition associated thermo-mechanical conditions, the microstructure exhibited fine equiaxed grains in the plane along the build direction along with bands of very fine grains within the interface regions between deposited layers. The observation of fine equiaxed grains and a lower degree of in-grain misorientation in the additively fabricated sample pointed to dynamic recrystallization as the governing restoration mechanism during the deposition process. The grain size refinement during additive friction stir deposition of IN625 resulted in substantial augmentation in the yield strength compared to IN625 feed material and as-cast IN625.

Numerical and experimental study on the thermal process during additive friction stir deposition

Additive friction stir deposition (AFSD) is a solid state coating process as well as a developing solid state additive manufacturing technology. AFSD has numerous advantages over friction surfacing coating technology. However, extensive research has demonstrated that a relationship between microstructure and mechanical properties exists at present. On the other hand, a few research focus on temperature field evolution.The temperature field during AFSD is examined in this paper using a combined experimental-numerical approach. According to characterizations of AFSD thermal process, AFSD was classified into friction preheating stages and steady deposition stages. The friction preheating model and the steady deposition heat model are both established. The experiment is carried out to confirm the temperature difference between the simulation and the experiment, where experimental and numerical results correspond well. The AFSD process parameters include rotational speed, feed speed, and deposition rate. The purpose of this research is to examine the effect of process parameters on heat input during the production of aluminum alloy coating by AFSD. The results shows that rotational speed is a critical element that influences heat input. Overall, the comparisons of experimental and numerical results show that the numerical model's accuracy is satisfactory, and the effect of process parameters on heat input was thoroughly investigated.

Novel approach in manufacturing aluminum-based alternate layered composite material via friction stir additive manufacturing route

The majority of today’s metal additive manufacturing techniques involve the transition of phases from liquid to solid, affecting their performance due to the microstructures formed during solidification. Employing novel solid-state additive manufacturing techniques like friction stir additive manufacturing (FSAM) helps to overcome these constraints. This study employed alternative layers of AA 6061-T6 and AA 7075-T6 aluminum alloys to construct defect-free alternate layered composite material (ALCM) via FSAM route using a single-pass (SP) weld strategy and double-pass (DP) weld strategy. The experiments were conducted by selecting the tool traverse speed, tool rotation speed and tool tilt angle as 40 mm/min, 1200 rpm and 2⁰ when AA 6061-T6 was set over AA 7075-T6 and 50 mm/min, 1100 rpm and 2⁰ when AA 7075-T6 was set over AA 6061-T6. A comprehensive investigation of the mixing of these dissimilar materials, changes in microstructure and microhardness, and variations in strength along the longitudinal direction in the stir zone (SZ) are evaluated in this study. Microstructures that evolved during both strategies were observed to be non-uniform, and equiaxed refined grains were identified in the SZ, which was recognized as the build’s most functional part. Repetitive stirring by the rotating tool decreased the average grain size and low-angle grain boundaries (LAGBs) along the SZ. The hardness and strength in the final build increased from lower layers to upper layers primarily due to the variation in grains and precipitate size. The highest value of hardness of 215.7 HV was identified in the topmost layer of DP technique, which was 15% higher when compared with the SP technique. Similarly, a 15% increase in strength was also observed in the topmost slice in the DP technique, whose value corresponds to 364 MPa. This study presents a summary of the results indicating that the use of a composite material consisting of alternating layers of AA 6061-T6 and AA 7075-T6 materials, which possess enhanced hardness and tensile strength, may serve as a viable replacement for the typical AA 6061 material often employed in automotive components. This substitution offers the potential for improved performance and increased lifespan.