摘要
采用填充镍基合金焊丝的方式对1.4 mm厚Al-Si镀层热成形钢进行激光焊接,对比分析了不同激光功率和送丝速度下接头微观组织的差异,深入探讨了合金元素对接头性能的影响。结果表明:镍基焊丝中的Ni和Co是强奥氏体稳定化元素,可以有效抑制Al元素的不利影响,确保包晶转变的彻底进行,从而抑制了焊缝中铁素体的形成;当焊缝中Ni的质量分数超过3.8%时,Al元素偏析被完全抑制,热成形前后的焊缝均为全马氏体组织;当焊缝中Ni的质量分数为6.47%时,M_(23)C_(6)、TiN等第二相粒子在马氏体基体中析出,进一步增强了焊缝强度;最佳焊接接头焊缝区域的平均硬度值为535 HV,抗拉强度为1643.5 MPa,与母材水平相当,接头断于母材侧。
Significance This study investigates the laser welding of 1.4 mm thick hotstamped steel with Al‒Si coating using nickelbased alloy filler metal.The microstructural differences in the weld joint under varying laser powers and feeding rates are systematically compared and analyzed.Additionally,the influence of alloying elements on the performance of the joints is thoroughly explored.The results demonstrate that Ni and Co,as strong austenitestabilizing elements in the nickelbased filler metal,effectively mitigate the adverse effects of aluminum(Al),preventing peritectic transformation and the formation of ferrite in the weld.When the mass fraction of Ni in the weld exceeds 3.8%,the segregation of the Al element is entirely suppressed,and the weld exhibits a fully martensitic structure before and after hot stamping.Furthermore,when the mass fraction of Ni in the weld is 6.47%,secondphase particles,such as M_(23)C_(6) and TiN precipitates,are observed in the martensitic matrix,further enhancing the strength of the weld.The optimal welding joint exhibits an average hardness of 535 HV and a tensile strength of 1643.5 MPa,comparable to the base metal.The joint is broken at the base metal.Progress The current research primarily focuses on using metal foil filling technology with a single alloying element to improve the laser welded joint strength of hotstamped steel with Al‒Si coating.However,the application of Ni foil filling technology is limited in its application scope in industrial production due to the complexity of the process and the uncontrollable content of introduced Ni.In view of this,this study proposes the use of nickelbased alloy welding wires for laser welding.By adjusting laser power and wire feeding speed,the alloy element content in the weld metal can be controlled effectively.From Figs.2(d)‒(f),it is evident that increasing the laser power further increases the amount of filler metal melted,resulting in a significant reduction ofδferrite within the weld seam of sample 2#,with only a small amount of smallsized particles present near the surface and fusion line.In sample 3#,an increased feeding speed leads to a higher Ni content in the weld seam.Figure 2(g)‒(i)shows that the weld seam of sample 3#exhibits a nearly fully martensitic structure,representing a significant improvement compared with that of samples 1#and 2#.Figure 3 displays the microstructure of the weld seam after laser welding and hot forming using nickelbased filler metal.From Figs.3(a)‒(c),it is clear that after hot forming,the weld seam of sample 1#transitions from the originalδferrite to a mixed structure of martensite andαferrite,with ferrite mass fraction around 18%.Figure 8 presents the tensile properties and fracture locations of the weld joints(1#,2#,and 3#)using nickel filler metal.The tensile curves reveal that the tensile strengths of all three groups are over 1630 MPa,comparable to the strength level of the base material.The curves for all specimens show significant plastic deformation,indicating a considerable improvement in tensile properties.Conclusions and Prospects The use of nickelbased alloy welding wires significantly improves the microstructure of weld seams.When the mass fraction of Ni in the weld exceeds 3.8%,aluminum segregation is effectively suppressed,resulting in a fully martensitic structure both before and after hot forming.With the mass fraction of Ni increases to 6.47%,secondphase particles such as M23C6 and TiN precipitate in the weld,with solid solution strengthening effects significantly enhancing the mechanical properties of the joint.Additionally,austenitestabilizing elements such as Ni and Co suppress the adverse effects of aluminum on the austenite phase,ensuring the complete peritectic transformation and suppressingδferrite formation.The optimal welding joint(sample 3#)welded with nickelbased wire exhibits excellent mechanical properties.The average hardness of the weld area reached 535 HV,and the tensile strength was up to 1643.5 MPa,comparable to the base metal.Furthermore,the fracture occurring on the base metal side indicates improved ductility of the welded joint.The uniform distribution of alloying elements such as Ni,Co,and Cr within the weld plays a critical role in enhancing the joint’s performance.Ni enhances weld strength by lowering the austenite transformation temperature and expanding the austenite phase field.The synergistic effects of Co and Cr further promote structural uniformity and optimal secondphase distribution.These elements significantly improve the mechanical properties of the weld joint through mechanisms such as solid solution strengthening and grain refinement.
作者
吴怡涵
陈贞韬
崔海超
唐新华
Wu Yihan;Chen Zhentao;Cui Haichao;Tang Xinhua(Shanghai Key Laboratory of Materials Laser Processing and Modification,School of Materials Science and Engineering,Shanghai Jiao Tong University,Shanghai 200240,China;CRRC Zhuzhou Locomotive Co.,Ltd.,Zhuzhou 412001,Hunan,China)
出处
《中国激光》
北大核心
2025年第8期79-90,共12页
Chinese Journal of Lasers
基金
国家重点研发计划(2023YFB3407800)
国家自然科学基金(U2141213)。
关键词
热成形钢
激光焊接
镍基焊丝
显微组织
力学性能
hotstamped steel
laser welding
nickelbased filler wire
microstructure
mechanical property
