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•AFS-D successfully deposited layers wider than the diameter of the tool offering a new path for large scale AM components.•Aluminum oxide films were dispersed by tool features and ...provided increased interlayer mixing.•More homogenous grain structures occurring from repeated stirring in overlapping region.•As-deposited tensile strength was unaffected by the overlapping region compared to similar AFS-D AA6061 single row studies.•Undispersed oxides dominated the fracture surface in place of typical secondary phase continuative particles.
In this paper, the effect of overlapping parallel additive depositions on microstructure and mechanical properties in Additive Friction Stir Deposition (AFS-D) was examined. In particular, the AFS-D process was employed to make parallel depositions of AA6061 with a 6.35 mm overlap to effectively bond the two parallel layers. The AFS-D process draws on similar physics to friction stir welding in that frictional heat and plastic deformation is exploited to deposit metallic materials from the center of a hollow rotating tool as it traverses across the build table to produce consecutive metallurgically bonded layers. In this work, the microstructural aspects of the 6.35 mm overlapping raster interface were characterized using optical and scanning electron microscopy. Aluminum oxide particles were observed at the raster interface, which were located at layer boundaries. Additional grain refinement was also apparent as a direct result of multiple stirring passes within the overlapping deposition region. Mechanical characterization via microindentation and monotonic tensile testing observed a hardness gradient in the overlapping region, but the parallel deposition layers exhibited comparable tensile strength to a single row of deposited AA6061. The influence of existing oxides on the mechanical results was observed to have limited effect on the properties longitudinally across the raster. This study determined that parallel layers of AA6061 can be successfully deposited via the AFS-D technique. The resulting deposit exhibited a strong metallurgical bond across the parallel layers despite the presence of surface oxidation on the unprepared feedstock and substrate.
In this study, the effect of post-deposition heat treatments on an Al–Mg–Si alloy processed with additive friction stir deposition (AFS-D), a solid-state additive manufacturing process, is examined. ...Results reveal that wrought-like microstructure and mechanical properties are achievable in AFS-D builds through the application of a post-deposition heat treatment.
► Twinning and detwinning was observed in the hysteresis loops of the AZ61 mg alloy. ► Fatigue cracks incubated from fractured intermetallic particles in the AZ61 mg alloy. ► Inclusions were more ...important in determining fatigue life than microstructure. ► The model predicted the different fatigue lives in the two orientations tested.
In this study, experiments were conducted to quantify structure-property relations with respect to fatigue of an extruded AZ61 magnesium alloy using a MultiStage Fatigue (MSF) model. Experiments were conducted in the extruded and transverse directions under low and high cycle strain control fatigue conditions. The cyclic behavior of this alloy displayed varying degrees of twinning and slip depending on the strain amplitude as observed in the hysteresis loops of both directions. Under low cyclic conditions, asymmetrical stress strain response was observed for both orientations. However, systematic stabilization of the hysteresis occurred by half-life due to subsequent twinning and detwinning mechanisms. In addition, under high cycle fatigue, pseudo-elasticity was observed at the first and at half-life cycles. Structure-property relations were quantified by examining the fracture surfaces of the fatigued specimens using a scanning electron microscope. In terms of crack incubation, fatigue cracks were found to initiate from intermetallic particles (inclusions) that were typically larger than the mean size. Quantified sources of fatigue crack incubation, microstructurally small cracks, and cyclic stress–strain behavior were correlated to the MSF model. Based on the specific material parameters, the MSF model was able to predict the difference in the strain-life results of the AZ61 magnesium alloy in the extruded and extruded transverse directions including the scatter of the experimental results. Finally, the MSF model revealed that the inclusion size was more important in determining the fatigue life than the anisotropic effects from the texture, yield, and work hardening.
In this work, a fully coupled thermo-mechanical meshfree approach is developed for the first time to simulate a solid-state layer-by-layer additive manufacturing process, Additive Friction ...Stir-Deposition (AFS-D). The meshfree method in this present work uses a Lagrangian reference frame, which permits tracking of material point history. A solid mechanics formulation is used, allowing the resolution of both elastic and plastic strains. An explicit dynamics time stepping scheme is used to ensure that the code is robust for the large level of non-linearity native to the AFS-D process. In this present work, a description of the meshfree method will first be described. Then a new thermo-mechanical joining contact algorithm will be introduced. Following that, a description of the experimental setup for the AFS-D model calibration experimental one layer deposition cases is explained. Subsequently, the simulation model and results for three different parameter sets will be detailed and compared against the experimental results. Finally, temperature and strain rate gradients are revealed across the entire deposition elucidating spatial-temporal flow phenomena in the AFS-D process.
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•Additive Friction Stir-Deposition simulations reveal inherent temperature and strain rate gradients.•Computationally efficient novel meshfree formulation facilitated by General-Purpose Computing on Graphics Processing Units.•Smoothed particle hydrodynamics simulations correlated to physical depositions representing acceptable and poor builds.•Simulations elucidate role of heat input on varying amounts of frictional heat generation influencing material flow.
Here we introduce a novel thermo-mechanical Solid State Additive Manufacturing (SSAM) process referred to as Additive Friction Stir (AFS) manufacturing that provides a new and alternative path to ...fusion-based additive manufacturing processes for developing fully-dense, near-net shape components with a refined-equiaxed grain morphology. This study is the first to investigate the beneficial grain refinement and densification produced by AFS in IN625 that results in advantageous mechanical properties (YS, UTS, εf) at both quasi-static and high strain rate. Electron Backscatter Diffraction (EBSD) observed grain refinement during the layer deposition in the AFS specimens, where the results identified fine equiaxed grain structures with even finer grain structures forming at the layer interfaces. The EBSD quantified grains as fine as 0.27µm in these interface regions while the average grain size was approximately 1µm. Additionally, this is the first study to report on the strain rate dependence of AFS IN625 through quasi-static (QS) (0.001/s) and high strain rate (HR) (1500/s) tensile experiments using a servo hydraulic frame and a direct tension-Kolsky bar, respectively, which captured both yield and ultimate tensile strengths increasing as strain rate increased. The HS results exhibited an approximately 200MPa increase in engineering strength over the QS results, with the fracture surfaces at both strain rates aligned with the maximum shear plane and exhibiting localized microvoids.
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•Dissimilar 6061 and 7050 aluminum alloys were joined via friction stir welding.•Variations in the degree of intermixing were correlated with tool rotational speed.•An increase in ...strength was observed with an increase in the tool rotational speed.•Fracture under tensile loading occurred on the AA6061 side of the joint.
In this work, the microstructure and mechanical properties of friction stir welded dissimilar butt joints of 6061-to-7050 aluminum alloys were evaluated. Microstructure analysis of the cross-section of the joints revealed distinct lamellar bands and various degrees of intermixing that were correlated with tool rotational speed. Due to the distinct mechanical properties of the two alloys, microhardness measurements showed a consistent asymmetric hardness distribution profile across the weld nugget, regardless of tool rotational speed. Under monotonic tensile loading, an increase in the joint strength was observed with the increase in the tool rotational speed. Regarding fracture, the joints consistently failed on the 6061 aluminum alloy side. Furthermore, two modes of failure were observed, one through the stir zone and the other through the heat-affected zone. Inspection of the fracture surfaces suggested that inadequate material intermixing produced at low tool rotational speeds was the cause for the low mechanical strength and failure through the stir zone. On the other hand, the failure observed through the heat-affected zone at high rotational speeds was produced due to the material softening as confirmed by the microhardness measurements.
The microstructure and lap-shear behaviors of friction stir linear welded wrought Al alloy AA6022-T4 to cast Mg alloy AM60B joints were examined. A process window was developed to initially identify ...the potential process conditions. Multitudes of welds were produced by varying the tool rotation rate and tool traverse speed. Welds produced at 1500 revolutions per minute (rpm) tool rotation rate and either 50mm/min or 75mm/min tool traverse speed displayed the highest quasi-static failure load of ~3.3kN per 30mm wide lap-shear specimens. Analysis of cross sections of untested coupons indicated that the welds made at these optimum welding parameters had negligible microvoids and displayed a favorable weld geometry for the cold lap and hook features at the faying surface, compared to welds produced using other process parameters. Cross sections of the tested coupons indicated that the dominant crack initiated on the advancing side and progressed through the weld nugget, which consists of intermetallic compounds (IMC). This study demonstrates the feasibility of welding wrought Al and cast Mg alloy via friction stir linear welding with promising lap-shear strength results.
A solid-state severe deformation-based additive manufacturing process, additive friction stir-deposition (AFS-D), offers an innovative solution to achieve wrought-like mechanical performance from ...metals that are susceptible to solidification cracking. In this work, the microstructural evolution and fatigue mechanisms of an Al-Zn-Mg-Cu alloy (AA7075) manufactured
via
a rapid solid-state deposition process are quantified for the first time. The AFS-D process deposits feedstock
via
frictional heat and severe plastic deformation, while avoiding the deleterious effects of solid–liquid phase transformation. A fully dense AA7075 deposit was manufactured without the need for additional alloying elements. The microstructural characterization of the as-deposited AA7075 employed optical, scanning electron microscope, and electron backscatter diffraction. The as-deposited AA7075 exhibited a refinement of the constituent particles and grains within the microstructure. Additionally, to quantify the fatigue behavior of the as-deposited AA7075, strain-life experiments were conducted, where a reduction in fatigue resistance was observed compared to the heat-treated feedstock, due to coarsening of strengthening precipitates
η
′ and
η
(MgZn
2
). Post-mortem analysis of the as-deposited AFS-D AA7075 revealed a change in the fatigue nucleation and growth mechanisms compared to the control feedstock. Lastly, a microstructure-sensitive fatigue life model was utilized to elucidate process-structure–property fatigue mechanism relations of the as-deposited and feedstock AA7075 materials.
Issues with rapid grain growth, hot cracking and poor ductility have hindered the additive manufacturing and repair of aluminum alloys. Therefore, this is the first investigation to spatially ...correlate the processing-structure-property relations of a precipitation hardened aluminum alloy 2219 (AA2219) material with respect to deposition orientations and build layers. The AA2219 material was processed by a high deposition rate (1000 cm3/h) solid-state additive deposition process known as Additive Friction Stir Deposition or MELD. An equiaxed grain morphology was observed in the three orientations, where Electron Backscatter Diffraction (EBSD) identified a layer-dependent texture with a strong torsional fiber A texture in the top of the build transitioning to weaker textures in the middle and bottom layers. Interestingly, the tensile behavior reflected the texture layer-dependence with tensile strength increasing from the bottom to the top of the deposition. However, there were no statistically significant differences in hardness measured from the top to the bottom of the deposition. Furthermore, no orientation dependence on mechanical properties was observed for compression and tension specimens tested at quasi-static (0.001/s) and high (1500/s) strain rate. Transmission Electron Microscopy (TEM) determined a lack of θ′ precipitates in the as-deposited cross-section, therefore resulting in no precipitation strengthening.
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In this work, the effect of processing parameters on the resulting microstructure and mechanical properties of magnesium alloy WE43 processed via Additive Friction Stir Deposition (AFSD), a nascent ...solid-state additive manufacturing (AM) process, is investigated. In particular, a parameterization study was carried out, using multiple four-layer deposits, to identify a suitable process window for a structural 68-layers bulk WE43 deposition. The parametric study identified an acceptable set of parameters with minimal surface defects and excellent consolidation for the fabrication of a bulk WE43 deposition. Microstructural, tensile, and fatigue life characterization was conducted on the bulk WE43 deposition and compared to commercially available wrought material to elucidate the process-structure-property-performance (PSPP) relationship of the AFSD process. This study shows that the bulk WE43 deposit exhibited a refined homogenous microstructure and a texture shift relative to the wrought material. However, a reduction in hardness and tensile behavior was observed in the as-deposited WE43 compared to the wrought control. Additionally, fatigue specimens extracted from the bulk deposition exhibited a decrease in life in the low-cycle regime but performed comparably to the wrought plate in the high-cycle regime. The outcomes of this study illustrate the potential of the AFSD process in additively manufactured structural load-bearing components made with magnesium alloy WE43 in the as-built condition.
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