중첩된 구리-알루미늄(Cu99.9-A5052) 판재의 전기저항가열 표면마찰 스폿용접(RSFSW)에 관한 연구

Abstract

In this work, a novel spot welding technology has been developed for joining pure copper/aluminum alloy sheets. A steel electrode with a friction rotating pin and a CuCrZr electrode act on the outside of the pure Cu/Al alloy sheets, respectively. This spot welding technology has two heating stages; firstly, resistance heat generated by the electric contact resistance between the steel electrode and the copper sheet and the high electric resistance of the steel electrode at a high alternating current of 8 kA. Secondly, after cutting welding current, the friction pin quickly rubs the outer surface of the copper sheet at a plunge rate of 4mm/min and a rotational speed of 1600 rpm, thereby producing a large amount of frictional heat. As a result, under the combined action of the resistance heat generated by 30 cycles of alternating current and the friction heat generated by the friction time of 1.5 seconds, the temperature of Cu/Al welding interface reached the melting point of the aluminum alloy, thereby realizing fusion welding. This spot welding technology has some welding variables such as current value, energizing cycles, rotational speed and friction time. Both current value and energizing cycles can affect the resistance heat, and the rotational speed of rotating pin and friction time also influence the generation of frictional heat. The resistance heating before the frictional heating not only has a preheating effect on the Cu/Al weld interface, but also can prevent the loss of frictional heat during the friction stage. However, the resistance preheating also softens the copper sheet, thereby affecting the contact stress and friction coefficient between the friction pin and the copper sheet, which will adversely affect the generation of frictional heat. Therefore, the optimal conditions can be found through the design of experiments method to balance the advantages and disadvantages of resistance preheating to the welding process. The new spot welding technology has several advantages as compared to the friction stir spot welding. For example, whirling structure can be formed under the action of plastic flow of material caused by rotational friction. It can increase the area of welding interface and improve the electrical conductivity and thermal conductivity, thereby enhancing the welding efficiency. In addition, since the welding temperature between Cu/Al weld interface mainly comes from the heat transfer from outer surface of copper sheet, It can avoid the drawbacks of large welding spacing caused by shunt effect for traditional resistance spot welding. In particular, the shorter weld spacing is very beneficial to the welding inside the automotive battery when the diameter of the battery cells inside the battery packs is generally small. Finally, the current study suggested that the new spot welding technology can improve the mechanical and electrical properties of non-ferrous metal sheet welded joints.