1998 Fiscal Year Final Research Report Summary
Elucidation of Porosity Formation Mechanism and Molten Flow Phenomenon
| Project/Area Number |
09650788
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Material processing/treatments
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| Research Institution | Osaka University |
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Principal Investigator |
KATAYAMA Seiji Joining and Welding Research Institute, Osaka University Associate Professor, 接合科学研究所, 助教授 (10144528)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUNAWA Akira Joining and Welding Research Institute, Professor, 接合科学研究所, 教授 (20029119)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Laser Welding / Welding Phenomenon / Welding Defects / Keyhole / Porosity / X-Ray Transmission Imaging / Plasma / Molten Flow |
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| Research Abstract |
The formation of bubble and porosity as well as keyhole behavior was observed during high power CO_2 laser welding of aluminum alloy A5083, stainless steel Type 304 and carbon steel in helium, argon and nitrogen shielding gas through micro-focused X-ray transmission imaging system.Moreover, plasma/plume and keyhole behaviors were simultaneously observed by utilizing two synchronized high-speed video cameras.Obtained results are as follows : (1) A keyhole behaved itself up and down violently, and many bubbles were generated from the bottom part of the keyhole, resulting in the formation of porosity of globular and elliptical shapes.(2) Evaporated particles and shielding gas were entrained, and partly hydrogen and atmosphere gases were included.(3) Oxide films were observed as a result of combination of evaporated elements Mg, Al and included oxygen in pores of laser welds in A5083 alloy.(4) Porosity was reduced in full penetration, beam-inclined forward welding, pulsed laser welding, etc.(5) Correlation was recognized between plasma/plume growth and a deepened keyhole in He gas, and when plasma/plume sustained to be large, the keyhole became shallower.(6) In argon and nitrogen gases, large gas plasma was observed in addition to plasma/plume, and it caused the keyhole to be diminished and eliminate just like pulsed welding.(7) The duration of pulsed welding under continuous wave laser irradiation was different according to the kind of shielding gas.(8) Porosity was extremely reduced in A5083 and Type 304 under such pulsed laser welding conditions.(9) Liquid flow was observed in wider or longer ranges in A5083 than Type 304 chiefly.(10) The liquid flow was attributed not to the buoyancy but to the evaporation of elements at the keyhole front surface.
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