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Raza, T., Hurtig, K., Asala, G., Andersson, J., Svensson, L.-E. & Ojo, O. A. (2019). Influence of Heat Treatments on Heat Affected Zone Cracking of Gas Tungsten Arc Welded Additive Manufactured Alloy 718. Metals, 9(8), Article ID 881.
Open this publication in new window or tab >>Influence of Heat Treatments on Heat Affected Zone Cracking of Gas Tungsten Arc Welded Additive Manufactured Alloy 718
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2019 (English)In: Metals, Vol. 9, no 8, article id 881Article in journal (Refereed) Published
Abstract [en]

The weldability of additive manufactured Alloy 718 was investigated in various heat-treated conditions. The microstructure of the base metal was examined in detail in order to understand the effect of different pre-weld heat treatments; i.e., solution, solution and aging, and hot isostatic pressing. After welding, the variation in total crack lengths, maximum crack length and the total number of cracks in the heat affected zone (HAZ) were used as criteria for the cracking susceptibility of each material condition where wrought Alloy 718 was used as the reference material. Selective laser melting (SLM) manufactured Alloy 718 was susceptible to HAZ cracking in all material conditions. Total crack lengths in HAZ were highest in the SLM as-built condition and lowest in the SLM hot isostatic pressed condition. The cracks that were found in the HAZ of the welded materials consisted of liquation cracks, with eutectic product surrounding the cracks, as well as cracks from which liquation products were absent.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
selective laser melting; Alloy 718; heat treatments; gas tungsten arc welding; heat affected zone cracking
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14595 (URN)10.3390/met9080881 (DOI)000484510000071 ()
Available from: 2019-10-16 Created: 2019-10-16 Last updated: 2019-10-16
Fahlström, K., Blackburn, J., Karlsson, L. & Svensson, L.-E. (2019). Low Porosity in Cast Magnesium Welds by Advanced Laser Twin-Spot Welding. Materials Sciences and Applications, 10(1), 53-64
Open this publication in new window or tab >>Low Porosity in Cast Magnesium Welds by Advanced Laser Twin-Spot Welding
2019 (English)In: Materials Sciences and Applications, ISSN 2153-117X, E-ISSN 2153-1188, Vol. 10, no 1, p. 53-64Article in journal (Refereed) Published
Abstract [en]

Porosity is reported to be a major issue when welding cast magnesium. Therefore, it is important to understand the pore formation mechanisms and find procedures that could be used to reduce porosity. This study investigated the possibility of using twin-spot optics for reducing the porosity in laser welded cast magnesium. Two twin-spot welding setups were compared using either a beam splitter or twin-spot welding with primary and secondary (placed in front of the primary optic) optics. The results showed that welding with a dual optic setup with a defocused secondary beam reduced the volumetric porosity in the weld to 5%. The highest levels of volumetric porosity were 30%, and were a result of using the dual optic setup, but with a defocused primary beam. No clear relation between the level of porosity and power or welding speed was found. It was found that the amount of porosity depended on the balance of the energy input (controlled by defocusing) between the two beams. Porosity formation can be reduced if the energy from the first beam results in the nucleation and initial growth of pores. Reheating by the second beam then allows the pores to grow and escape from the molten material without melting additional base material. Furthermore, twin-spot welding is shown to be a promising combination of a production friendly solution and high quality welding.

Keywords
Laser Welding, Cast Magnesium, Twin-Spot, Metallurgy, Porosity, Automotive, AM50 Alloy
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-13753 (URN)10.4236/msa.2019.101006 (DOI)
Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-01Bibliographically approved
Li, P., Hurtig, K., Högström, M., Svensson, L.-E. & Scotti, A. (2018). A contribution to the study of negative polarity in GMA welding. The International Journal of Advanced Manufacturing Technology, 95(5-8), 2543-2553
Open this publication in new window or tab >>A contribution to the study of negative polarity in GMA welding
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2018 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 95, no 5-8, p. 2543-2553Article in journal (Refereed) Published
Abstract [en]

GMAW using the electrode with negative polarity (DCEN) has been frequently suggested as a potential means of increasing production capacity. The objective of this work was to further study the performance of negative polarity in GMAW of carbon steels. In this project phase, bead-on-plate welds were carried out in flat position to assess the effect of different potential shielding gas compositions on bead geometry, finishing and spattering. The characteristics were compared with DCEP at the same current, but depositing the same volume of material per unit of length (more industrial related comparison). The arc length was kept the same by adjusting voltage to reach shortest arcs, yet with suitable non short-circuiting metal transfer mode. An approach to measure bead convexity was also proposed and assessed. The results showed that DCEN is feasible as a means of increasing GMAW production capacity. However, to become DCEN applicable with GMAW, the results suggest an Ar based blend with around 6.5 % of O2 is the most appropriate shielding gas, as much as that there is a demand for a standard electronic controlled power source able to work in constant current mode. 

Keywords
Welding; Production; GMAW; Negative Polarity; Fusion rate; Weld bead geometry
National Category
Other Mechanical Engineering Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-11817 (URN)10.1007/s00170-017-1349-z (DOI)2-s2.0-85035104454 (Scopus ID)
Projects
Maplab
Funder
Region Västra Götaland, RUN 612-0254-15
Note

Funders: Swedish Agency for Economic and Regional Growth, 20200328.

Available from: 2017-11-26 Created: 2017-11-26 Last updated: 2019-05-28Bibliographically approved
Fahlström, K., Blackburn, J., Karlsson, L. & Svensson, L.-E. (2018). Effect of Laser Welding Parameters on Porosity of Weldsin Cast Magnesium Alloy AM50. Modern Approaches on Material Science, 1(2), 25-32
Open this publication in new window or tab >>Effect of Laser Welding Parameters on Porosity of Weldsin Cast Magnesium Alloy AM50
2018 (English)In: Modern Approaches on Material Science, ISSN 2641-6921, Vol. 1, no 2, p. 25-32Article in journal (Refereed) Published
Abstract [en]

Pores in the weld metal lower the mechanical properties of the weld. It is therefore important to understand the pore formation mechanisms and find procedures that could reduce porosity. This study focused on laser welding of 3 mm thick magnesium alloy AM50, investigating how different parameters affect porosity formation. Low levels of porosity content were achieved by either increasing the welding speed or using a two-pass welding approach. It was found that higher welding speeds did not allow pores,which were pre-existing from the die-casting process, to have sufficient time to coalesce and expand. In the two-pass welding technique, pores were removed as a result of a degassing process which occurred through the second pass.

Keywords
Laser welding; Magnesium, Cast; Metallurgy; Porosity; Automotive; AM50
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13754 (URN)10.32474/MAMS.2018.01.000106 (DOI)
Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-10-23Bibliographically approved
Segerstark, A., Andersson, J., Svensson, L.-E. & Ojo, O. (2018). Effect of Process Parameters on the Crack Formation in Laser Metal Powder Deposition of Alloy 718. Metallurgical and Materials Transactions. A, 49A(10), 5042-5050
Open this publication in new window or tab >>Effect of Process Parameters on the Crack Formation in Laser Metal Powder Deposition of Alloy 718
2018 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 10, p. 5042-5050Article in journal (Refereed) Published
Abstract [en]

Cracking in Alloy 718 using laser metal powder deposition has been evaluated in this study. It is found that the material is susceptible to cracking when the laser power is high, the scanning speed is high and the powder feeding rate is low. Almost all the cracks are located close to the center of the deposited wall and propagates in the normal direction to the substrate. Evidence of liquation are found at the cracked surfaces and since all cracks reside in regions which are reheated several times, the cracks are determined to mostlikely be heat affected zone liquation cracks. The influence of respective process parameter was evaluated using a design of experiment approach. It is shown that, when the powder feeding rate is incorporated as avariable, the heat input is not a suitable indicator for the hot cracking susceptibility in laser metal powder deposition of Alloy 718. A combinatory model using the power ratio together with the heat input is therefore proposed.

Keywords
Laser Metal Deposition, Additive manufacturing, Powder, Superalloy, Cracking, Characterization
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11841 (URN)10.1007/s11661-018-4767-0 (DOI)000443469700064 ()2-s2.0-85049122881 (Scopus ID)
Funder
Region Västra GötalandSwedish Agency for Economic and Regional Growth
Note

Ingår i avhandling och det finns ett tidigare publicerat manuskript.

Available from: 2017-11-29 Created: 2017-11-29 Last updated: 2019-03-05Bibliographically approved
Karimi Neghlani, P., Raza, T., Andersson, J. & Svensson, L.-E. (2018). Influence of laser exposure time and point distance on 75-μm-thick layer of selective laser melted Alloy 718. The International Journal of Advanced Manufacturing Technology, 94(5-8), 2199-2207
Open this publication in new window or tab >>Influence of laser exposure time and point distance on 75-μm-thick layer of selective laser melted Alloy 718
2018 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 94, no 5-8, p. 2199-2207Article in journal (Refereed) Published
Abstract [en]

A systematic matrix with 25 samples, using five different point distances and five laser exposure times, depositing 75-μm-thick layers of Alloy 718 has been studied. The work has concentrated on defects formed, hardness of the deposits, and the microstructure. Relatively large amount of defects, both lack of fusion and porosity, was found in several of the specimens in the deposits. The defects were never possible to fully eliminate, but a significant decrease, mainly in the lack of fusion, was seen with increasing laser exposure time. The gas porosity on the other hand was not affected to any larger degree, except for the lowest laser energy input, where a slight increase in porosity was seen. A small increase in hardness was noted with increasing laser energy input. The width of the deposited beads increased with increasing laser energy, while the depth of deposits was more or less constant. However, for the lowest combination of point distance and laser exposure time, quite deep and narrow beads were formed. A comparison was made with deposition of 50-μm-thick layers, with quite similar laser energy input, but with some variation in detailed deposition parameters. It was found that the 75-μm-thick layers contained less lack of fusion, particularly for small point distances. The amount of porosity was also less, but that did not vary with deposition parameters.© 2017 The Author(s)

Keywords
3D printers; Defects; Deposition; Deposits; Hardness; Microstructure, Alloy 718; Deposition Parameters; Large amounts; Laser energies; Laser exposure; Point distances; Selective laser melting; Small points, Porosity
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11886 (URN)10.1007/s00170-017-1019-1 (DOI)000422886200055 ()2-s2.0-85028818109 (Scopus ID)
Funder
VinnovaSwedish National Space Board
Note

First Online: 06 September 2017

Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2019-05-28Bibliographically approved
Segerstark, A., Andersson, J., Svensson, L.-E. & Ojo, O. (2018). Microstructural Characterization of Laser Metal Powder Deposited Alloy 718. Materials Characterization, 142, 550-559
Open this publication in new window or tab >>Microstructural Characterization of Laser Metal Powder Deposited Alloy 718
2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 142, p. 550-559Article in journal (Refereed) Published
Abstract [en]

A microstructural study of Laser Metal Powder Deposition (LMPD) of Alloy 718, using a low (40 J/mm) and high (100 J/mm) heat inputs (HIs) was performed. The microstructure was characterized in as-deposited condition as well as after a standard heat-treatment, using optical microscope (OM), scanning electron microscope (SEM) and Transmission Electron Microscope (TEM). Laves, MC-carbides, γ' and γ'' are observed in the interdendritic areas of both conditions. However, the dendritic core only consists of γ-matrix. The high HI condition shows a slightly larger Primary Dendrite Arm Spacing (PDAS) as compared to the low HI condition. Additionally, the particle size of the Nb-rich constituents in the interdendriticregions (Laves-phase and Niobium carbide) are larger in the high HI sample. After heat-treatment, the Laves phase dissolves and is replaced by δ-phase in the interdendritic regions, while γ', γ'' and MC-carbideremain in the interdendritic regions. However, the γ'' precipitates seems to be less developed in the dendritic core as compared to the interdendritic regions, especially in the high HI sample. This can be attributed to a heterogeneous distribution of Nb in the microstructure, with a lower Nb content in the dendritic core as compared to close to the interdendritic regions.

Keywords
Laser Metal Deposition, Additive manufacturing, Powder, Superalloy, Microstructure
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11840 (URN)10.1016/j.matchar.2018.06.020 (DOI)000440527300060 ()2-s2.0-85048865443 (Scopus ID)
Funder
Region Västra GötalandSwedish Agency for Economic and Regional Growth, 2015/392 820
Note

Ingår i avhandling med tidigare publicerat manuskript.

Available from: 2017-11-29 Created: 2017-11-29 Last updated: 2019-05-27Bibliographically approved
Raza, T., Andersson, J. & Svensson, L.-E. (2018). Microstructure of Selective Laser Melted Alloy 718 in As-Manufactured and Post Heat Treated Condition. Paper presented at 8th Swedish Production Symposium, SPS 2018; Waterfront Convention CentreStockholm; Sweden; 16 May 2018 through 18 May 2018; Code 147722. Procedia Manufacturing, 25, 450-458
Open this publication in new window or tab >>Microstructure of Selective Laser Melted Alloy 718 in As-Manufactured and Post Heat Treated Condition
2018 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 450-458Article in journal (Refereed) Published
Abstract [en]

Manufacturing of Alloy 718 with selective laser melting (SLM) process faces several challenges. One of the challenges is the process-induced porosities in as-manufactured SLM parts. Another challenge is the microstructure of Alloy 718 that contains a high amount of segregating elements, such as MC-type carbides and γ/Laves phase eutectics in interdendritic regions. The microstructural heterogeneity in the as-manufactured SLM part unavoidably leads to mechanical heterogeneity and hence, post-processing heat treatments become necessary to achieve a homogeneous microstructure. Therefore, by investigating various post heat treatment options the knowledge on how to decrease/eliminate these segregations will be developed. © 2018 Elsevier B.V. All rights reserved.

Keywords
Selective laser melting, Alloy 718, Process parameters, Post heat treatments
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13921 (URN)10.1016/j.promfg.2018.06.100 (DOI)2-s2.0-85065659917 (Scopus ID)
Conference
8th Swedish Production Symposium, SPS 2018; Waterfront Convention CentreStockholm; Sweden; 16 May 2018 through 18 May 2018; Code 147722
Funder
VinnovaSwedish National Space Board
Available from: 2019-06-05 Created: 2019-06-05 Last updated: 2019-07-26Bibliographically approved
Raza, T., Andersson, J. & Svensson, L.-E. (2018). Varestraint weldability testing of additive manufactured alloy 718. Science and technology of welding and joining, 23(7), 606-611
Open this publication in new window or tab >>Varestraint weldability testing of additive manufactured alloy 718
2018 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 23, no 7, p. 606-611Article in journal (Refereed) Published
Abstract [en]

The weldability in terms of susceptibility towards hot cracking of selective laser melted (SLM) Alloy 718 was investigated and wrought Alloy 718 was used as reference material. Varestraint testing was carried out by means of investigating the weldability in three conditions; (1) SLM as-built, (2) hot isostatic pressing at 1160°C at 105MPa for 3h and (3) wrought Alloy 718 in the mill-annealed condition. The material exhibited intergranular cracking in all three conditions; however,theSLMHIPedconditionhadanincreasedmagnitudeofcracksusceptibilityatallstrain levels.TheincreasedsensitivityoftheHIPedmaterialwasduetothesignificantlylargergrainsize incomparison.TheSLMas-builtconditionshowedthesamedegreeofcrackingasthewrought material.

Keywords
Weldability; Selective laser melting; Alloy718
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12077 (URN)10.1080/13621718.2018.1437338 (DOI)000440719100008 ()2-s2.0-85041916665 (Scopus ID)
Funder
VINNOVASwedish National Space Board
Note

Published online: 12 Feb 2018

Available from: 2018-02-13 Created: 2018-02-13 Last updated: 2019-01-28Bibliographically approved
Harati, E., Karlsson, L., Svensson, L.-E. & Dalaei, K. (2017). Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels. International Journal of Fatigue, 97, 39-47
Open this publication in new window or tab >>Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels
2017 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 97, p. 39-47Article in journal (Refereed) Published
Abstract [en]

Application of Low Transformation Temperature (LTT) consumables in welding is a recent approach to increase the fatigue strength of welds. In this paper high strength steels with yield strengths ranging from 650-1021 MPa were fillet and butt welded using different LTT and conventional consumables. The effects of weld metal chemical composition on phase transformation temperatures, residual stresses and fatigue strength were investigated. Lower transformation start temperatures and hence lower tensile or even compressive residual stresses were obtained close to the weld toe for LTT welds. Fatigue testing showed very good results for all combinations of LTT consumables and high strength steels with varying strength levels. For butt welds, the characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to 46% higher when compared to corresponding welds made with conventional filler materials. In fillet welds, a minimum FAT improvement of 34% and a maximum improvement of 132% was achieved when using LTT wires. It is concluded that different LTT consumables can successfully be employed to increase fatigue strength of welds in high strength steels with yield strength up to 1021 MPa. Weld metals with martensite transformation start temperatures close to 200°C result in the highest fatigue strengths.

Keywords
Low Transformation Temperature Welding Consumables, Fatigue Strength, Residual Stress, Martensite Start Temperature
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10212 (URN)10.1016/j.ijfatigue.2016.12.007 (DOI)000393631300005 ()2-s2.0-85007154275 (Scopus ID)
Available from: 2016-12-05 Created: 2016-12-05 Last updated: 2017-08-23Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2560-0531

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