低功率激光辐照对弯曲成形件表面残余应力的影响

目的 针对航空铝合金构件维修加工后存在残余拉应力,进而影响部件使用寿命的难题,研究一种基于低能量输入激光辐照消减构件表面残余应力的方法.方法 采用激光辐照材料残余应力集中区域,通过激光热作用诱导弹性内能转化为塑性功,从而降低残余应力.为了验证该方法的可行性,对2A12铝合金试样进行四点弯曲加载,通过不均匀塑性变形产生残余应力,再通过激光扫描应力集中区域诱导表面残余应力局部释放.结果 采用X射线衍射法测量表面残余应力的结果表明,激光扫描后,试样表面的残余拉应力完全消除,当激光功率增大到95 W时,残余应力可以消除77％左右.通过理论分析和微观形貌对比,发现材料在激光辐照前后并没有相变.通过分析材料Al(311)晶面X射线衍射峰半高宽的变化,发现激光辐照使材料表面位错密度下降,随着激光功率增大,位错密度下降幅度增大,这也是残余应力降低的原因之一.结论 在不改变材料微观组织的前提下,采用低功率激光辐照可以显著降低材料表面残余应力分布.

Effect of Low-power Laser Irradiation on the Surface Residual Stress of Bending Part

Aiming at the problem of the residual tensile stress of aeronautical aluminum alloy parts after repair and processing, which affects the service life of components, a method based on low-energy input laser irradiation to reduce the surface residual stress of components is studied. The laser beam irradiates the concentration area of the residual stress,converting the elastic internal energy into plastic work by laser heating, resulting in the residual stress reduced. In order to verify the feasibility of this approach, four-point bending test was conducted on the 2A12 aluminum alloy sample, the residual stress was caused by the non-uniform plastic deformation during the bending. The laser radiating relieved the residual stress by scanning the stress concentration region. The surface residual stress of the sample was measured via X-ray diffraction. The results showed that the residual stress decreased significantly after laser scanning, and the tensile residual stress was completely eliminated. When the laser power was increased to 95 W, the compressive residual stress could be eliminated by around 77%. Through theoretical analysis and microscopic morphology comparison, it was found that no phase transformation occured before and after laser scanning. By analyzing the variation of the full width at half maximum for the diffraction peak of Al (311) crystalline plane, it was found that the laser heating decreased the dislocation density. With the increase of laser power, the decrease of dislocation density increases, which was one of the reasons for residual stress relaxation. Without changing the microstructure of the material, low-power laser irradiation could significantly reduce the surface residual stress distribution of the material.