镍箔对DP980/A6061异种激光焊接接头组织性能的影响

Effect of Nickle Foil on Microstructure Properties of DP980/A6061 Dissimilar Laser Welded Joints

对DP980板和A6061板进行了激光搭接焊试验,对比分析了镍箔对焊接接头焊缝(WS)和熔合线(FL)的显微组织、显微硬度及拉剪性能的影响。结果表明,对于未添加镍箔样品,铝元素进入熔池内导致WS和FL处形成大量软质相δ铁素体和部分板条马氏体(LM),钢/铝界面处析出脆性FeAl_2、FeAl_3金属间化合物,金属间化合物层的峰值厚度约为50μm,拉伸过程中焊接接头在界面处发生脆性断裂;对于添加镍箔样品,镍元素抑制了Fe-Al冶金反应的进行,促使δ铁素体向奥氏体转变,在室温下WS获得了全LM组织,WS硬度升高,界面处形成了Ni-Al金属间化合物,界面处的硬度和脆性Fe-Al金属间化合物层的厚度减小。镍箔使焊接接头的强度提高至61 MPa,是未添加镍箔样品的1.4倍。

The experiment of the laser overlapped welding for the DP980 and A6061 sheets is conducted and the influences of the nickel foil on the microstructure, the microhardness and the tensile shear property of the weld seam （WS） and the fusion line （FL） of the laser welded joints are compared and analyzed. The results show that, as for the sample without the nickel foil, the entry of the Al element into the weld pool results in the formation of a large number of soft phase 3 ferrites and some lath martensites （LM） within the WS and FL. The brittle intermetallic compounds of FeAl2 and FeAl3 separate out near the steel-Al interface, whose peak thickness is about 50 ~m, and thus there occur brittle fractures of welded joints at the interface during the tensile process. In contrast, as for the sample with the nickel foil, the nickel element effectively suppresses the Fe-Al metallurgical reaction, and thus the transformation of 3 ferrites into austenite is promoted. At room temperature, the WS obtains the full LM microstructure. The WS hardness increases, there occurs the Ni-Al intermetallic compound near the interface, and both the hardness at interface and the thickness of the Fe-Al intermetallic compound layer decrease. The nickel foil makes the laser welded joint strength increase up to 61 MPa, which is 1.4 times that of the sample without the nickel foil.