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Influence of aluminium powder aging on Directed Energy deposition
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0002-0649-0130
Department of Mechanical Engineering, Politecnico di Milano, 1 Via Privata Giuseppe La Masa, 20156 Milano, Italy.
Department of Mechanical Engineering, Politecnico di Milano, 1 Via Privata Giuseppe La Masa, 20156 Milano, Italy.
Fraunhofer, Institut für Werkstoff und Strahltechnik, Winterbergstraße 28, 01277 Dresden, Germany.
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2022 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 218, article id 110677Article in journal (Refereed) Published
Abstract [en]

The use of aluminium alloys for Additive Manufacturing is of high interest for advanced geometries and lightweight applications. In Directed Energy Deposition, a powder stock is processed with a laser beam, which offers a high process flexibility. However, aging of the powder feedstock during storage or after recycling remains fundamentally challenging for aluminium alloys because of their sensitivity to oxida-tion and porosity. In order to investigate these effects, AlSi10Mg powder batches were aged in different conditions and processed by Directed Energy Deposition. The results showed that powder aging does not significantly change the particle size or morphology, but it introduces more oxygen and hydrogen in the powder. The oxidation of the particles reduces the laser beam absorbance of the powder and increases wetting of the melt pool, which affects the track geometry. A 3.5 to 4.2 times higher porosity was observed in the material deposited from aged powder, which are most likely hydrogen pores causedby the increased hydrogen content in the aged powder. The tensile properties of the parts built with aged powder showed 19.0% lower yield strength, 14.2% lower ultimate strength and 99.2% higher elongation, which are most likely the results of the coarser microstructure and increased porosity.

Place, publisher, year, edition, pages
Elsevier, 2022. Vol. 218, article id 110677
Keywords [en]
Direct Metal Deposition, Laser Metal Deposition, Laser Powder Bed Fusion, Oxidation, Porosity
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-90849DOI: 10.1016/j.matdes.2022.110677ISI: 000800225800004Scopus ID: 2-s2.0-85129120353OAI: oai:DiVA.org:ltu-90849DiVA, id: diva2:1663069
Projects
SAMOA (no. 18079)
Note

Validerad;2022;Nivå 2;2022-06-02 (sofila);

Funder: EIT Raw Materials.

Available from: 2022-06-01 Created: 2022-06-01 Last updated: 2023-09-04Bibliographically approved
In thesis
1. Aspects of material and heat transfer in drop- and powder-based laser additive manufacturing
Open this publication in new window or tab >>Aspects of material and heat transfer in drop- and powder-based laser additive manufacturing
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Additive Manufacturing became a major research topic and part of industrial production in the past years. Numerous techniques now allow to build 3D structures with a wide choice of materials. When it comes to processing of metals, a laser beam is often used as a heat source to melt either a wire or powder. Novel approaches of material deposition are also developed, such as Laser Droplet Generation, which could potentially be applied to Additive Manufacturing. During the process, the laser beam light is partly absorbed by the material, and is then converted to heat, which can induce melting and even vaporization. Additive Manufacturing presents several processing challenges, such as the recoil pressure acting on the drops and powder particles that affects their trajectory. Storage and recycling of the powders is also an important aspect since the powder properties are changed through aging. Another challenge is the adjustment of process parameters according to varying deposition conditions, where the use of process monitoring techniques is crucial.

Therefore, this thesis aims at better understanding (i) the effects of recoil pressureon metal drops and powder particles, (ii) powder aging and its effects on the process, and (iii) process optimisation and stability via monitoring. In the six adjoined papers, high-speed imaging and thermal imaging were used to observe laser Additive Manufacturing processes involving both metal drops and powders. The videos enabled to observe drop detachments, measure trajectories, plot powder density maps, quantify powder catchment in the melt pool, measure themelt pool geometry, detect oxides, and extract cooling rates. The experimental results were supplemented with material analysis and theoretical calculations of thermodynamics, recoil pressure and surface tension.

These studies allowed to conclude that the recoil pressure induced by laser irradiation on a drop or a powder particle can have some significant effect such as acceleration, change of trajectory, or disintegration. However, these effects seem to be considerably lower than what theoretical models predict. It was also found that the recoil pressure can be used to accurately detach drops from a wire, which was utilised as a new material deposition method for Additive Manufacturing. In Directed Energy deposition, it was showed that aging of the aluminium powder feedstock should be avoided since it induces high porosity, high dilution and decreased mechanical properties. Finally, to guarantee a defect-free deposition during the whole process, it was demonstrated that a thermal camera can be used to monitor the melt pool size, which allows to apply appropriate laser power adjustments to compensate for changing building conditions.  

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2023
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-95798 (URN)978-91-8048-280-6 (ISBN)978-91-8048-281-3 (ISBN)
Public defence
2023-05-03, E632, Luleå tekniska universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2023-03-07 Created: 2023-03-07 Last updated: 2023-09-01Bibliographically approved

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Da Silva, AdrienBrandau, BenediktFrostevarg, JanKaplan, Alexander

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