| 학회 | 한국재료학회 |
| 학술대회 | 2020년 가을 (11/18 ~ 11/20, 휘닉스 제주 섭지코지) |
| 권호 | 26권 1호 |
| 발표분야 | 특별심포지엄1. 최신 용접/접합기술 및 용접재료 개발 동향 심포지엄-오거나이저: 김양도(부산대) |
| 제목 | Study of Effect of the Electrode degradation on Weldability during Electrode Life Test in Resistance Spot Welding of Ultra-High Strength Steel |
| 초록 | The automotive industry is continuously in search of lightweight components, energy-saving technology, and thereby reducing the overall costs of the car bodies. In view of these demands, car designers are showing interest in ultra-high-strength steels (UHSS) with tensile strength above 780MPa and to follow the crash safety and fuel efficiency regulation. UHSSs have more resistance spot weldability issues compared with the conventional high-strength steels (HSS) and the mild steels owing to their high bulk resistance induced by rich alloying concentrations and the narrow contact area between the sheet and the electrode. Weld metal expulsion occurs easily, and the weldable current range becomes narrower. Owing to the requirement of continuous resistance spot welding process in automobile industries, the resistance spot weldability is inevitable. However, very few there is no research on evaluation about this. Therefore, this study aimed at the evaluation of resistance spot weldability of ultra-high strength steel in resistance spot welding considering the continuous process. In this study, an evaluation of weldability was carried out through an electrode life test, and weldability testing was performed by the measurement of nugget size, the peak load analysis and the measurement of the electrode tip size at 30 welds intervals. Analysis of the change in the size of nuggets indicated a trend of rapid decrease. Moreover, the peak load showed that there was a rapid decrease until the 150th weld spot and then a slight increase until the 360th spot weld. The crack and cavity in the weld nugget and the protrusion of the weld pool were mostly observed after the 150th weld spot. Unlike the previous study, the electrode tip size steadily decreased during welding. The decreased electrode tip size could be explained by the narrow contact area between the electrode and sheet during welding, which would account for the continuous occurrence of sticking and expulsion between the electrode and the sheet. A geometric deformation occurred at the edge of the electrode owing to the deformation of the electrode without any alloying, whereas the region which was in contact with the sheet experienced Cu-Zn-Fe alloying. As a result, frequent electrode sticking with the TRIP steel sheet caused the formation of protrusions and cavities on the electrode surface. Thus, the localized electrode degradation can be divided into three regions: region III where the electrode was undergoing wear and geometric deformation, region II where the protrusion occurred, and region I where the cavity was formed. Finally, the electrode degradation in the resistance spot welding of ultra-high strength steels is defined as “plateau formation” that is due to the geometric as well as metallurgical changes which contradict the existing “mushrooming effect”. |
| 저자 | 김재원1, Siva Prasad Murugan2, 강남현3, 박영도2 |
| 소속 | 1한국생산기술(연), 2동의대, 3부산대 |
| 키워드 | Resistance Spot Welding; Ultra-High Strength Steel; Electrode Degradation; Plateau Formation; |
