摘要
采用激光熔钎焊技术进行镁/钢异种材料的搭接试验,通过添加镍中间层调控焊缝成分,并通过外加纵向交变磁场调控接头的组织形貌,从而提升接头的力学性能。试验结果表明:强烈的电磁搅拌促进了镁、镍、铁元素之间的扩散与反应;外加交变磁场后,镁侧焊缝熔池中的带状Fe-Ni固溶体使接头的机械咬合作用增强,金属间化合物层的类熔焊区与类钎焊区未生成树枝状AlNi,类熔焊区形成的连续的纳米级AlNi层对接头具有强化作用,提高了接头的力学性能。接头的拉剪强度随着励磁电流I_(E)与励磁频率f的增加呈先增大后减小的趋势,当激光功率P=1250 W,焊接速度v=20 mm/s,I_(E)=1.2 A,f=35 Hz时,接头的拉剪强度最高,达到了228 MPa,比无交变磁场时提高了约15%。
Objective Universal demands to reduce energy consumption and emissions have elevated the role of lightweight design in the fields of aviation,ship,and automobile.These demands can be satisfied using Mg/steel dissimilar materials welding;however,many problems must be considered when attempting to realize a high-quality connection between Mg alloy and steel.The physical,chemical,and mechanical properties of Mg alloy and Fe are quite different.In addition,they are immiscible,and no intermetallic compounds are produced between Fe and Mg.Currently,to solve this problem,the formation of interfacial compounds is promoted by adding or coating an Ni,Cu,Ag,Zn,Sn,Cu-Zn,and Zn-x Al interlayer.Applying alternating magnetic field during laser welding process mainly brings two effects,including skin effect and electromagnetic force.When an alternating magnetic field is applied,liquid metal will produce an alternating induced current,which has a skin effect.In addition,the magnetic field and induced current produce an electromagnetic force;the alternating electromagnetic force promotes the positive and negative rotation of the molten pool,and convection in the molten pool is intensified.Previous studies have shown that the external alternating magnetic field can improve the weakness of joint compounds in the welding process of Mg/steel dissimilar materials.Ni can form intermetallic compounds and a solid solution with Mg and Fe,respectively.An alternating magnetic field is expected to regulate the distribution of compounds,which will improve the mechanical properties of joints.Therefore,laser welding-brazing technology assisted by alternating magnetic field is adapted to Mg/steel dissimilar materials welding with Ni interlayer.Microstructure and mechanical properties of the joint with and without alternating magnetic field are compared.The Mg/steel dissimilar metal connection with the Ni interlayer technology is further improved by applying an alternating magnetic field,and relevant data support is provided.Methods Experimental materials included AZ31 B Mg alloy and Q235 low carbon steel.The dimensions of Mg alloy and steel plates were 120 mm×60 mm×1 mm.A 0.1 mm thick pure Ni foil(99.9%)was used as the interlayer.The dimensions of the Ni foil were 60 mm×10 mm×0.1 mm.A 6 k Wfiber laser(IPG YLS-6000 CUT)was used for welding,and the laser beam was focused as a spot with a 0 mm diameter on the plates.During welding,the top surface of the plates was protected by argon with 99%purity at a flow of 15 L/min.AZ31 B Mg alloy was lapped on Q235 low carbon steel with a clamp,and a 0.1 mm Ni foil was sandwiched between Mg alloy and the Q235 low carbon steel.After welding,the sample was cut along the direction perpendicular to the weld seam using a wire cutting machine,and the inlay was made using an XQ-1 hot mosaic machine and then polished.According to a preliminary test,the optimum welding parameters were P=1250 W,v=20 mm/s;the alternating magnetic field parameters were excitation current,IE=0.8--2.0 A(every 0.2 A is an increasing unit)and excitation frequency,f=15--55 Hz(every 10 Hz is an increasing unit).Scanning electron microscope and energy dispersion spectrometer were used to study the cross-section morphology,Mg side weld zone,steel side weld zone,and intermetallic compound(IMC)layer of the joint under longitudinal alternating magnetic field.A WDW-100 electronic universal tensile testing machine was used to conduct tensile and shear tests on the joint.The tensile rate was 0.5 mm/min.Three groups of samples were stretched with each parameter.The average value of the three groups of parameters was calculated to determine the corresponding tensile and shear strength.Results and Discussion The diffusion and reaction of Mg,Ni,and Fe elements in weld metal were promoted by strong electromagnetic stirring after applying the alternating magnetic field(Figs.3 and 4).The appearce of zonal structures of Fe-Ni solid solution in the weld pool of Mg side weld zone and the serrated Mg2 Ni in the brazing zone of the IMC layer enhanced the mechanical bite effect.A continuous nanoscale Al Ni layer was formed in the fusion welding zone,and this strengthened the joint(Figs.5 and 6).With increased excitation current IE and excitation frequency f,the tensile and shear strengthσb of the joint initially increased and then decreased.For P=1250 W,v=20 mm/s,IE=1.2 A,and f=35 Hz,the maximumσb of the joint reached 228 MPa,which wasapproximately 15%higher than that without the magnetic field(Fig.8).Conclusions It is expected that the compound distribution of Mg/steel joints can be controlled by applying an alternating magnetic field,and the mechanical properties of the joints can be improved.The diffusion and reaction of Mg,Ni,and Fe elements in weld metal were promoted via strong electromagnetic stirring after applying the alternating magnetic field.The appearance of zonal structures of the Fe-Ni solid solution in the weld pool of the Mg side weld zone and the serrated Mg_(2)Ni in the brazing zone of the IMC layer enhanced the mechanical bite effect.A continuous nanoscale Al Ni layer was formed in the fusion welding zone,and it strengthened the joint.With increased excitation current IE and excitation frequency f,the tensile and shear strength σ_(b) of the joint increased initially and then decreased.For P=1250 W,v=20 mm/s,I_(E)=1.2 A,and f=35 Hz,the maximumσb of the joint reached 228 MPa,which is approximately 15%higher than that without the magnetic field.
作者
戎易
程东海
熊震宇
陈益平
刘钊泽
Rong Yi;Cheng Donghai;Xiong Zhenyu;Chen Yiping;Liu Zhaoze(School of Aeronautical Manufacturing Engineering,Nanchang Hangkong University,Nanchang Jiangxi330063 China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2021年第22期44-53,共10页
Chinese Journal of Lasers
基金
国家自然科学基金(51965045)。
关键词
激光技术
激光熔钎焊
交变磁场
机械咬合
金属间化合物层
拉剪强度
laser technique
laser welding-brazing technology
alternating magnetic field
mechanical bite
IMC layer
tensile and shear strength
