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Investigation of Gas Metal Arc Welding as a Potential Method for Additive Manufacturing of Magnesium Alloys.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Investigation of Gas Metal Arc Welding as a Potential Method for Additive Manufacturing of Magnesium Alloys./
Author:	Kossack, Christoph Andreas Johann.
Description:	1 online resource (176 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-02, Section: B.
Contained By:	Dissertations Abstracts International85-02B.
Subject:	Mechanical engineering. -
Online resource:	click for full text (PQDT)
ISBN:	9798380074872

Investigation of Gas Metal Arc Welding as a Potential Method for Additive Manufacturing of Magnesium Alloys.
Kossack, Christoph Andreas Johann.

Investigation of Gas Metal Arc Welding as a Potential Method for Additive Manufacturing of Magnesium Alloys. - 1 online resource (176 pages)

Source: Dissertations Abstracts International, Volume: 85-02, Section: B.

Thesis (Ph.D.)--The University of North Carolina at Charlotte, 2023.

Includes bibliographical references

Gas Metal Arc Welding (GMAW) was investigated as a method for the rapid Wire Arc Additive Manufacturing (WAAM) of magnesium alloys. The GMAW deposition process that was tested was not modified with Cold Metal Transfer (CMT) or short-circuit deposition. High and low input-energy-rate (IER) parameters were established to deposit weld beads with limited spatter and good bead shape. Single-bead multilayer walls were deposited by a GMAW-CNC using 1.2 mm diameter AZ61a welding wire. These walls were deposited at two different torch travel speeds (TTS) but with the same IER of 1,700 W. The walls were machined into thin walls and wire EDM (WEDM) was used to extract tensile test specimens. Half of the test coupons were extracted so that the tensile test pull force is in-line with the deposition direction and the other half were extracted with the pull force being applied normal to the print direction. For the samples printed at the same TTS, the Instron test results showed high repeatability and a material yield strength (YS) of 116 MPa. The YS for these samples was independent of print orientation, showing the isotropic behavior of the printed material. The samples that were printed at a faster TTS showed the same response to loading conditions, but had a lower YS of 106 MPa, demonstrating how an increase in TTS lowers the YS of welded material. The stress at fracture, however, was almost identical for all the samples, with fractures occurring between 260 MPa and 270 MPa.Multi-row/multi-layer (MRML) blocks were also printed out of the same material and tested, also with half the samples being extracted normal to the Instron applied load and the other half in-line with the pull force. A higher IER of 2,700 W was implemented to ensure fusion between the over-lapping beads. The same isotropic behavior was observed in these samples but the YS increased in relation to the single wall, low IER samples by over 20 MPa to 139 MPa. Due to the presence of larger internal defects caused by bead overlap issues, the fracture strength range was very spread out, with some normal-to-force samples fracturing at less than 150 MPa and some in-line to force samples fracturing at around 220 MPa. The results for the elastic region, however, fit that of the thin-wall samples.Scanning Electron Microscope (SEM) analysis was performed on the fracture surface, showing ductile behavior in the fused regions, but also uncovering material defects in the MRML samples such as trapped spatter, trapped air bubbles, and cracks. Optical micrographs were obtained to analyze the microstructure of the samples. A grain refinement from 38 µm pre-weld down to 12 µm post-weld for the MRML samples and a grain refinement down to 28 µm for the single-bead multilayer walls was determined, demonstrating how a reduction of degrees of freedom for conduction heat transfer to occur will result in a larger grain size due to decreased cooling rates.Multi-layer hollow cylinders were printed to test the ability of the method to produce closed-shape parts. These cylinders were produced at both high and low IERs and yielded parts with post-machining wall thicknesses ranging from 1.5 mm to 4.5 mm. X-ray Computed Tomography (XCT) was performed to determine the porosity of these parts. The three sections analyzed showed a total part percent porosity of 0.04 %, 0.039 %, and 0.07%. Larger individual defects, particularly at the closure-of-bead zone were detected, resulting in maximum single layer %-porosity of 0.8 %.Finally, a Finite Element Analysis (FEA) model was created to simulate the deposition of the beads and the heat transfer throughout the process. The element activation feature in COMSOL Multiphysics was coupled with the simulated torch path to model the deposition of the material. Heat transfer modes of conduction, radiation, and convection were conditionally assigned to the boundaries of the substrate and of the beads as functions of time and material deposition. The Goldak double-ellipsoid heat source was used as the primary heating method of the substrate. To simulate the true-to-life GMAW process, where already molten material drops onto the substrate, a bead-heating function was created and applied to the inactive elements of the bead that is being deposited during the simulation. This was done to ensure that the temperatures of the simulated weld droplets are at the correct estimated temperature when they are first activated, after which only normal heat transfer modes impact the temperature of the now active elements. The inactive elements have the assigned properties of air until being activated. The model successfully simulates the thermal-load cycles the part undergoes during the deposition of a 3-by-3 beads block. The results show how in WAAM the layer height is directly correlated to the maximum temperatures seen in the part due to the reduction in directions for heat transfer to occur, with substrate height layers reaching 1300 K and layers 2 and 3 rising to 1500 K and 1700 K, respectively.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798380074872Subjects--Topical Terms:

557493
Mechanical engineering.
Subjects--Index Terms:

Additive manufacturingIndex Terms--Genre/Form:

554714
Electronic books.

Investigation of Gas Metal Arc Welding as a Potential Method for Additive Manufacturing of Magnesium Alloys.
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504 $a Includes bibliographical references
520 $a Gas Metal Arc Welding (GMAW) was investigated as a method for the rapid Wire Arc Additive Manufacturing (WAAM) of magnesium alloys. The GMAW deposition process that was tested was not modified with Cold Metal Transfer (CMT) or short-circuit deposition. High and low input-energy-rate (IER) parameters were established to deposit weld beads with limited spatter and good bead shape. Single-bead multilayer walls were deposited by a GMAW-CNC using 1.2 mm diameter AZ61a welding wire. These walls were deposited at two different torch travel speeds (TTS) but with the same IER of 1,700 W. The walls were machined into thin walls and wire EDM (WEDM) was used to extract tensile test specimens. Half of the test coupons were extracted so that the tensile test pull force is in-line with the deposition direction and the other half were extracted with the pull force being applied normal to the print direction. For the samples printed at the same TTS, the Instron test results showed high repeatability and a material yield strength (YS) of 116 MPa. The YS for these samples was independent of print orientation, showing the isotropic behavior of the printed material. The samples that were printed at a faster TTS showed the same response to loading conditions, but had a lower YS of 106 MPa, demonstrating how an increase in TTS lowers the YS of welded material. The stress at fracture, however, was almost identical for all the samples, with fractures occurring between 260 MPa and 270 MPa.Multi-row/multi-layer (MRML) blocks were also printed out of the same material and tested, also with half the samples being extracted normal to the Instron applied load and the other half in-line with the pull force. A higher IER of 2,700 W was implemented to ensure fusion between the over-lapping beads. The same isotropic behavior was observed in these samples but the YS increased in relation to the single wall, low IER samples by over 20 MPa to 139 MPa. Due to the presence of larger internal defects caused by bead overlap issues, the fracture strength range was very spread out, with some normal-to-force samples fracturing at less than 150 MPa and some in-line to force samples fracturing at around 220 MPa. The results for the elastic region, however, fit that of the thin-wall samples.Scanning Electron Microscope (SEM) analysis was performed on the fracture surface, showing ductile behavior in the fused regions, but also uncovering material defects in the MRML samples such as trapped spatter, trapped air bubbles, and cracks. Optical micrographs were obtained to analyze the microstructure of the samples. A grain refinement from 38 µm pre-weld down to 12 µm post-weld for the MRML samples and a grain refinement down to 28 µm for the single-bead multilayer walls was determined, demonstrating how a reduction of degrees of freedom for conduction heat transfer to occur will result in a larger grain size due to decreased cooling rates.Multi-layer hollow cylinders were printed to test the ability of the method to produce closed-shape parts. These cylinders were produced at both high and low IERs and yielded parts with post-machining wall thicknesses ranging from 1.5 mm to 4.5 mm. X-ray Computed Tomography (XCT) was performed to determine the porosity of these parts. The three sections analyzed showed a total part percent porosity of 0.04 %, 0.039 %, and 0.07%. Larger individual defects, particularly at the closure-of-bead zone were detected, resulting in maximum single layer %-porosity of 0.8 %.Finally, a Finite Element Analysis (FEA) model was created to simulate the deposition of the beads and the heat transfer throughout the process. The element activation feature in COMSOL Multiphysics was coupled with the simulated torch path to model the deposition of the material. Heat transfer modes of conduction, radiation, and convection were conditionally assigned to the boundaries of the substrate and of the beads as functions of time and material deposition. The Goldak double-ellipsoid heat source was used as the primary heating method of the substrate. To simulate the true-to-life GMAW process, where already molten material drops onto the substrate, a bead-heating function was created and applied to the inactive elements of the bead that is being deposited during the simulation. This was done to ensure that the temperatures of the simulated weld droplets are at the correct estimated temperature when they are first activated, after which only normal heat transfer modes impact the temperature of the now active elements. The inactive elements have the assigned properties of air until being activated. The model successfully simulates the thermal-load cycles the part undergoes during the deposition of a 3-by-3 beads block. The results show how in WAAM the layer height is directly correlated to the maximum temperatures seen in the part due to the reduction in directions for heat transfer to occur, with substrate height layers reaching 1300 K and layers 2 and 3 rising to 1500 K and 1700 K, respectively.
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653 $a Magnesium alloys
653 $a Microstructure
653 $a Yield strength
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710 2 $a The University of North Carolina at Charlotte. $b Mechanical Engineering. $3 1148582
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