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目的 研究激光熔覆过程中离焦量对熔覆层成形质量的影响. 方法 在扫描速度(2 mm/s)和送粉电压(8 V)不变的情况下,通过改变熔覆头与基体间的距离和激光功率,对比分析不同离焦量对熔覆层尺寸、洛氏硬度、界面显微硬度和金相组织的影响,并确定最佳离焦量. 结果 当离焦量DL=3,4 mm时,熔覆层表面硬度先逐渐增大后趋于稳定,洛氏硬度高达55~56HRC;当离焦量DL=5,6 mm时,由于离焦量过大,导致基体与熔覆层冶金结合不牢固,部分粉末颗粒没有充分熔化附着在熔覆层表面,熔覆层质量较差. 同一功率下,随着离焦量的增大相对熔覆层宽度会减小;当离焦量DL=3 mm时,冷却速度最大、熔覆层底部由柱状晶沿着熔体最易散热方向生长明显,在熔覆层上部形成了等轴晶组织. 结论 激光熔覆时离焦量是不可忽视的工艺参数之一,最终优化工艺参数为:扫描速度2 mm/s,送粉电压8 V,激光功率1200 W,最佳离焦量3 mm.

Objective To study the influence of defocusing amount on the forming quality of the cladding layer during the laser cladding process. Methods When the speed was kept constant at 2 mm/s and the voltage was 8 V, the influence of different defo-cusing amount on cladding size, Rockwell hardness, interface microhardness and microstructure was comparatively analyzed by changing the distance between the head of cladding and the substrate as well as the laser power. The optimal defocus amount was determined. Results The surface hardness of the cladding layer first increased gradually and then tended to be stable, and Rock-well hardness reached up to 55~56HRC when the defocusing amount was 3 mm or 4 mm. Since the defocus amount was too large,the metallurgical bonding between the substrate and the cladding layer was weak, and part of the powder was not fully melted and attached to the cladding layer surface, so that the quality of cladding was poor when the defocusing amount was 5 mm or 6 mm. Un-der constant power, the cladding layer width decreased with the increasing defocusing amount. When the defocusing amount was 3 mm, the maximum cooling rate was achieved, and columnar crystals were most likely to grow along the melt radiating, leading to the formation of equiaxed crystal structure on top of the cladding layer. Conclusion Defocusing amount is one of the important process parameters in laser cladding. The finally optimized process parameters were v=2 mm/s,U=8 V,P=1200 W,DL=3 mm.