激光冲击强化对焊缝组织性能影响的研究进展

Research Progress on the Effect of Laser Shock Processing Technology on the Microstructure and Properties of Weld

激光冲击强化(LSP)是一种典型的非弹丸撞击式表面强化技术,可有效提高金属材料的抗疲劳能力、抗腐蚀能力、金属耐磨性能和使用寿命,具有应变率高、效率高、强化效果好等优点。焊缝质量直接影响了焊接件的合格率,而焊缝强化一直是一个比较难的挑战。首先,介绍了激光冲击强化的加工原理,总结了激光冲击强化的影响参数及条件,包括激光功率密度、约束层和吸收层、激光冲击次数、光斑搭接率以及激光脉宽。控制强化工艺参数可以使焊缝显微硬度提升50%、残余压应力提升65%以上,大幅度提升抗拉强度,降低疲劳裂纹扩展。其次,综述了国内外研究人员运用激光冲击强化技术对不同材料焊缝强化的研究与应用,重点论述了激光冲击强化对焊缝力学性能和显微组织的显著强化效果,与未强化试样对比,强化后试样的各项性能明显提升。其中针对力学性能,详细分析了显微硬度、残余应力和疲劳裂纹扩展的变化情况,结合残余应力的理论研究、仿真分析、试验论证以及显微组织变化情况,认为激光冲击强化导致马氏体组织发生了碎化,提高了硬度,产生了残余压应力,引起了晶粒细化,进而有效控制了疲劳裂纹扩展,阻止了裂纹产生,提升了疲劳寿命。通过激光冲击强化不同工艺参数的协同作用,可以获得较高的残余压应力和硬度,引起动态再结晶、晶粒细化等微观组织演变以及位错运动,使焊缝力学性能和显微组织产生相互影响。分析认为,激光冲击强化技术是焊缝强化的有效焊接后处理工艺。最后,展望了激光冲击强化技术在焊缝强化领域中的应用前景。

Laser shock processing(LSP)is a typical non projectile impact surface strengthening technology,which can effectively improve the fatigue resistance,corrosion resistance,wear resistance and service life of metal materials.It has the advantages of high strain rate,high efficiency and good strengthening effect.In recent years,with the rapid development of aerospace and automobile manufacturing,the good property of weldments becomes more and more important.The excellent weld quality directly affects the qualification rate of weldments,and weld strengthening has always been a difficult challenge.Firstly,the principle of laser shock processing was introduced,and the parameters and conditions affecting laser shock processing were summarized,including laser power density,constraint layer and absorbing protective layer,laser shock times,spot overlap rate and laser pulse width.By controlling different strengthening process parameters,the microhardness of weld could be increased by 50%,the residual comprehensive stress could be increased by more than 65%,the tensile strength could be greatly improved and the fatigue crack propagation could be reduced.Then,the research and application of laser shock processing technology used by researchers in China and abroad were summarized to strengthen the welds of different materials,and the significant strengthening effect of laser shock processing on the mechanical properties and microstructure of the weld was discussed in particular.By controlling the combination of different shock strengthening process parameters,the process effect could be improved.Compared with the unstrengthened samples,the properties of strengthened samples were significantly improved.In terms of mechanical properties,the changes of microhardness,residual stress and fatigue crack propagation were analyzed in detail,and the reasons for different changes of microhardness of aluminum alloy were expounded.The experimental effects of strengthening in weld zone,heat affected zone and base metal zone were compared and introduced.It was found that the microhardness could be increased by 20%-80%.Combined with the theoretical research,simulation analysis and experimental synchronous demonstration of residual stress,it is considered that laser shock processing can effectively control the fatigue crack growth and improve the fatigue life by increasing the residual stress,but the coupling of many factors makes the crack growth uncertain,which can be discussed through orthogonal test to obtain the best parameter combination.By analyzing the microstructure changes after laser shock processing,it is considered that laser shock processing can transform the grains into equiaxed grains through twinning,resulting in dislocation substructure and a large amount of deformation as well as grain refinement.Grain refinement can slow down the crack propagation and prevent the occurrence of cracks.Therefore,the mechanism of laser shock strengthening grain refinement is obtained.Under the synergistic effect of different laser shock processing parameters,the microstructure evolution such as dynamic recrystallization and grain refinement and dislocation movement can increase the residual stress and hardness,resulting in the interaction between mechanical properties and microstructure.It is considered that laser shock processing technology is an effective post welding treatment process for weld strengthening.Finally,the application prospect of laser shock processing technology in the field of weld strengthening is prospected.