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Low Porosity in Cast Magnesium Welds by Advanced Laser Twin-Spot Welding
University West, Department of Engineering Science, Research Enviroment Production Technology West. Swerea KIMAB, Kista, Sweden. (PTW)ORCID iD: 0000-0001-8933-6720
TWI Ltd., Cambridge, UK.
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0001-8822-2705
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0003-2560-0531
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.

Place, publisher, year, edition, pages
2019. Vol. 10, no 1, p. 53-64
Keywords [en]
Laser Welding, Cast Magnesium, Twin-Spot, Metallurgy, Porosity, Automotive, AM50 Alloy
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-13753DOI: 10.4236/msa.2019.101006OAI: oai:DiVA.org:hv-13753DiVA, id: diva2:1301247
Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-01Bibliographically approved
In thesis
1. Laser welding of ultra-high strength steel and a cast magnesium alloy for light-weight design
Open this publication in new window or tab >>Laser welding of ultra-high strength steel and a cast magnesium alloy for light-weight design
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There is a strong industrial need for developing robust and flexible manufacturing methods for future light-weight design. Better performing, environmental friendly vehicles will gain competitive strength from using light weight structures. In this study, focus has been on laser welding induced distortions for ultra-high strength steel (UHSS) where trials were performed on single hat and double hat beams simulating A-pillar and B-pillar structures. Furthermore, also laser welding induced porosity in cast magnesium alloy AM50 for interior parts were studied. For UHSS, conventional laser welding was done in a fixture designed for research. For cast magnesium, single-spot and twin-spot welding were done. Measurements of final distortions and metallographic investigations have been performed. The results show that the total weld metal volume or the total energy input were good measures for predicting the distortions within one steel grade. For comparing different steel grades, the width of the hard zone should be used. The relation between the width of the hard zone, corresponding to the martensitic area of the weld, and the distortions is almost linear. Additionally, compared with continuous welds, stitching reduced the distortions. For cast magnesium, two-pass (repeated parameters) welding with single-spot gave the lowest porosity of approximately 3%. However, two-pass welding is not considered production friendly. Twin-spot welding was done, where the first beam provided time for nucleation and some growth of pores while reheating by the second beam should provide time for pores to grow and escape. This gave a porosity of around 5%. Distortions and porosity are the main quality problems that occur while laser welding UHSS and cast magnesium, respectively. Low energy input seems to generally minimize quality issues. Laser welding shows high potential regarding weld quality and other general aspects such as productivity in light-weight design for both high strength steel and cast magnesium.

Place, publisher, year, edition, pages
Trollhättan: University West, 2019. p. 94
Series
PhD Thesis: University West ; 29
Keywords
Laser welding, ultra-high strength steel, cast magnesium alloy, light-weight design, automotive industry, distortion, porosity
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-13752 (URN)978-91-88847-29-4 (ISBN)978-91-88847-28-7 (ISBN)
Public defence
2019-04-24, F131, Trollhättan, 10:00 (English)
Opponent
Supervisors
Available from: 2019-04-02 Created: 2019-04-01 Last updated: 2019-04-01Bibliographically approved

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Fahlström, KarlKarlsson, LeifSvensson, Lars-Erik

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