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 MSA  Vol.10 No.1 , January 2019
Low Porosity in Cast Magnesium Welds by Advanced Laser Twin-Spot Welding
Abstract: 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.
Cite this paper: Fahlström, K. , Blackburn, J. , Karlsson, L. and Svensson, L. (2019) Low Porosity in Cast Magnesium Welds by Advanced Laser Twin-Spot Welding. Materials Sciences and Applications, 10, 53-64. doi: 10.4236/msa.2019.101006.
References

[1]   Kielbus, A., Rzychon, T. and Cibis, R. (2006) Microstructure of AM50 Die Casting Magnesium Alloy. Journal of Achievements in Materials and Manufacturing Engineering, 18.

[2]   Harooni, M., et al. (2014) Pore Formation Mechanism and Its Mitigation in Laser Welding of AZ31B Magnesium Alloy in Lap Joint Configuration. Materials and Design, 58, 265-276.
https://doi.org/10.1016/j.matdes.2014.01.050

[3]   Zhu, J., Li, L. and Liu, Z. (2005) CO2 and Diode Laser Welding of AZ31 Magnesium Alloy. Applied Surface Science, 247, 300-306.
https://doi.org/10.1016/j.apsusc.2005.01.162

[4]   Cao, X., et al. (2005) Continuous Wave ND:YAG Laser Welding of Sand Cast ZE41A-T5 Magnesium Alloys. Materials and Manufacturing Processes, 20, 987-1004.
https://doi.org/10.1081/AMP-200060436

[5]   Cao, X., et al. (2006) A Review of Laser Welding Techniques for Magnesium Alloys. Journal of Materials Processing Technology, 171, 188-204.
https://doi.org/10.1016/j.jmatprotec.2005.06.068

[6]   Gertsman, Y., et al. (2005) Microstructure and Second-Phase Particles in Low- and High-Pressure Die-Cast Magnesium Alloy AM50. Metallurgical and Materials Transactions A, 36, 1989-1997.
https://doi.org/10.1007/s11661-005-0319-5

[7]   Fredriksson, H. and Akerlind, U. (2006) Materials Processing during Casting. John Wiley & Sons, Chichester.
https://doi.org/10.1002/9780470017920

[8]   Ma, Y., Zhang, J. and Yang, M. (2009) Research on Microstructure and Alloy Phases of AM50 Magnesium Alloy. Journal of Alloys and Compounds, 470, 515-521.
https://doi.org/10.1016/j.jallcom.2008.03.047

[9]   Lee, G., et al. (2006) Effect of Process Parameters on Porosity Distributions in High-Pressure Die-Cast AM50 Mg-Alloy. Materials Science & Engineering A, 427, 99-111.
https://doi.org/10.1016/j.msea.2006.04.082

[10]   Harooni, M., et al. (2012) Mitigation of Pore Generation in Laser Welding of Magnesium Alloy AZ31B in Lap Joint Configuration. ASME-International Mechanical Engineering Congress & Exposition Proceedings, Houston.

[11]   Wahba, M., et al. (2012) Laser Welding of Die-Cast AZ91D Magnesium Alloy. Materials and Design, 33, 569-576.
https://doi.org/10.1016/j.matdes.2011.05.016

[12]   Wahba, M. and Katayama, S. (2012) Laser Welding of Magnesium Alloy. Transactions of JWRI, 41, 11-23.

[13]   Liu, L., et al. (2005) Pore Formation during Hybrid Laser-Tungsten Inert Gas Arc Welding of Magnesium Alloy AZ31B—Mechanism and Remedy. Materials Science and Engineering A, 390, 76-80.
https://doi.org/10.1016/j.msea.2004.07.067

[14]   Zhang, J., et al. (2013) Reducing the Porosity in Die-Cast Magnesium Alloys during Laser Welding. Welding Journal, 92, 101-109.

[15]   Zhao, H. and Debroy, T. (2001) Pore Formation during Laser Beam Welding of Die Cast Magnesium Alloy AM60B—Mechanism and Remedy. Weld Journal, 80, 204s-210s.

[16]   Fahlstrom, K., et al. (2018) Effect of Laser Welding Parameters on Porosity of Welds in Cast Magnesium Alloy AM50. The 71st IIW Annual Assembly & International Conference, Nusa Dua.

[17]   Harooni, M., et al. (2015) Two-Pass Laser Welding of AZ31B Magnesium Alloy. Journal of Materials Processing Technology, 216, 114-122.
https://doi.org/10.1016/j.jmatprotec.2014.08.028

[18]   Shibata, K., et al. (2003) Welding of Aluminium Car Body Parts with Twinspot High-Power Nd: YAG Laser. Welding International, 17, 939-946.
https://doi.org/10.1533/wint.2003.3201

[19]   Harooni, M., et al. (2014) Dual-Beam Laser Welding of AZ31B Magnesium Alloy in Zero-Gap Lap Joint Configuration. Optics & Laser Technology, 56, 247-255.
https://doi.org/10.1016/j.optlastec.2013.08.018

[20]   Rasband, W. and Image, J. (2016) National Institutes of Health. Image Processing Program.

[21]   Haboudou, A., et al. (2003) Reduction of Porosity Content Generated during Nd:YAG Laser Welding of A356 and AA5083 Aluminium Alloys. Materials Science and Engineering A, 363, 40-52.
https://doi.org/10.1016/S0921-5093(03)00637-3

 
 
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