损伤曲轴的激光熔覆修复是实现发动机高质量再制造的关键技术之一。为提高因磨损、擦伤和烧伤等缺陷导致报废的曲轴激光熔覆修复的稳定性与可靠性, 首先采用YAG固体激光器对磨损损伤曲轴主轴颈进行熔覆, 进而采用手持显微镜与扫描电子显微镜(SEM)相结合的方法对熔覆层周向与径向宏观形貌和微观组织进行观测分析, 利用显微硬度仪测试沿深度和表面母线方向的微硬度值, 利用X射线应力测试仪对熔覆层表面残余应力测试。最后, 对熔覆层与基体的过渡层、熔覆浅表层等熔覆质量较差的区域以及中间质量优化区进行量化表达, 为获得最佳质量工作表面的熔覆余量等参数的确定提供依据。研究结果表明, 微观组织沿深度方向呈平面胞状晶-胞状树枝晶-树枝晶和等轴晶变化, 沿母线方向存在组织细致的结合区, 熔覆层显微硬度较基体提高2.6倍, 表面残余应力为压应力, 其中沿扫描方向的平均残余应力值为-400.8 MPa, 垂直于扫描方向的平均残余应力值-278.5 MPa。

The repair of damaged crankshaft by laser cladding is one of the key technologies to achieve high-quality engine remanufacturing. In order to improve the stability and reliability of the laser cladding repaired scrapped crankshaft caused by wear and tear, abrasions and burns and other defects, YAG solid laser was used to repair the worn crankshaft main journal. The macro morphology and microstructure of circumferential and radial cladding layer were observed and analyzed by handheld microscope and scanning electron microscope(SEM). Microhardness along the depth direction and the direction of surface generatrix were tested using a microhardness tester. Besides that, the surface residual stresses of the samples were measured by X-ray stress analyzer. The cladding quality of the transitional layer of cladding layer and matrix, the areas with poor cladding quality such as cladding surface and middle quality optimization area were quantified and characterized. This providing a guidance to control cladding allowance and get the optimum quality of the final surface. The results show that the microstructure along the depth direction evolves from planar cellular crystal, cellular dendrite, dendrite and equiaxed crystal. The small and compact microstructure of the bonding zone appears along the direction of the generatrix. The microhardness of the cladding layer is 2.6 times higher than that of the substrate. The surface residual stress of the cladding layer is compressive stress, the average residual stress along the scan direction is -400.8 MPa, and average residual stress perpendicular to the scanning direction is -278.5 MPa.