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Vol.35, No.5, 590 ~ 601, 1997
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| Title |
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| 정재훈 , 김도훈 , 유병호 , 이경돈 , 장낙영 Jae Hoon Chung , To Hoon Kim , Byung Kil Yu , Kyoung Don Lee , Nag Young Chang |
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| Abstract |
| This work is the basic research on the tailored blank laser welding of automobile low carbon steel sheets. The materials used were low carbon steel sheets for automotive bodies, which were welded together in equal thickness(0.9㎜/0.9㎜). In order to make a practical application of the tailored blank laser welding, conditions for laser welding should be optimised. Experiments were carried out by applying the Taguchi method. The advantage of the application of Taguchi method (calculated by S/N(Signal to Noise) ratio) is to reduce the amount of experiments and is to estimate the interaction between various parameters. Optical microscopy, SEM, TEM and XRD analysis were performed to observe the microstructures in the fusion zone and to determine the phase and solidification mode. The microstructure of fusion zone was consisted of fine grains with dendrites due to rapid solidification (cooling rate was estimated to 10⁴K/s). The fusion zone had a mixed phases of quasi-polygonal ferrite, martensite and undefined phase which had a transformation temperature between that of quasi-polygonal ferrite and martensite. Since an important property of the laser welded tailored blank is formability, the formability of the base metal and welded specimens were examined through tensile test, dome height test and microhardness test. The elongation and LDH of welded specimens were found to be more than 80% of the base metal. Optimum laser welding conditions could ensure reasonable formability for the laser welded tailored blank (automobile low C steel sheet). |
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