자동차 차체용 알루미늄 합금의 저항 용접 특성 비교 및 가압력 제어 영향에 대한 고찰

Abstract

This study was performed to compare the resistance spot weldability of Al 5052-H32 alloy and Al 6014-T4 alloy used for automobile bodies and investigated the effect of electrode-force control. In general, the surface of the aluminum alloy has an oxide film several nm thick, and local heat input is generated at the electrode-sheet interface and the sheet-sheet interface. This reason carried out the problems such as contamination of the electrode surface, expulsion, defects in the weld metal, etc., and the weldability is poor. To improve the weldability of aluminum alloy in resistance spot welding, much research has been performed in terms of process and material, and the weldability could be improved than before. However, methods that can fundamentally improve weldability in terms of material are not presented, and the improvement methods suggested to improve weldability in terms of the process are practically difficult to apply to on-site process lines, and production costs increase. Therefore, this study compared the welding characteristics of the two alloys with different solute elements during resistance spot welding and investigated the factors that fundamentally hinder weldability, And also the effect of electrode-force control highly field-applicable was investigated.

First, as a result of examining the weldability of the Al 5052-H32 alloy and the Al 6014-T4 alloy, the Al 5052-H32 alloy, which has a relatively thick magnesium oxide film on the surface and contains a large amount of magnesium solute element, has a higher resistance to both contact resistance of the interface-sheet interface and sheet-sheet interface and intrinsic resistance of the sheet and electrode than the Al 6014-T4 alloy. Therefore, the Al 5052-H32 alloy has a larger nugget diameter at the same welding current as compared to the Al 6014-T4 alloy, but the surface contamination of the electrode is aggravated owing to local heat input. In addition, Al 5052-H32 alloy had more pores and shrinkage in the weld than Al 6014-T4 alloy, and longitudinal cracks were observed in the center of the nugget but had relatively excellent mechanical properties.

The second study investigated electrode-force type controls to improve the weldability of the aluminum alloy. It was found that a high electrode-force on squeeze time can collapse the Al2O3 oxide film on the surface. It can reduce defects in the nugget by about 42%, by reducing heat input energy, compared to the continuous electrode-force 4 kN (reference value). Also, with high electrode-force during the hold time, defects were reduced by about 80%, by increasing the cooling rate. The weld quality has a great influence on the electrode-force type control, and internal defects in the nugget are greatly affected by the electrode-force on hold time.