活塞杆表面激光熔覆硬度和残余应力的数值模拟

Numerical Simulation of Hardness and Residual Stress of Laser Cladding Coating on Piston Rod Surface

针对20钢表面采用激光熔覆M2粉末后涂层难以同时获得低残余应力和高硬度的问题,通过建立活塞杆和涂层有限元模型,设定活塞杆不同的预热温度,仿真分析得到不同预热温度下残余应力和硬度的变化规律。结果表明,工件残余应力和硬度与激光熔覆后工件冷却速度有很大的关系,预热辅助可以降低工件冷却速度、减小残余应力,但是同时对涂层硬度有明显影响。激光熔覆前设置活塞杆不同的预热温度并随室温冷却,活塞杆径向和轴向残余应力随着预热温度的升高出现下降趋势。与未预热工况比较,当预热300~475℃时,涂层硬度基本没有变化,熔合区和热影响区硬度减小;当预热500℃时,涂层、熔合区及热影响区硬度都开始明显减小。在相同的室温(20℃)条件下,活塞杆预热至475℃后进行激光熔覆与未预热的工况相比,径向最大残余应力下降了39.8%,轴向最大残余应力下降了42.1%,涂层硬度基本无变化。结论,预热活塞杆温度至475℃后开始激光熔覆有利于降低涂层残余应力,同时可以获得较好的涂层硬度。

It is difficult to obtain low residual stress and high hardness after laser cladding M2 powder coating on the surface of 20 steel at the same time.In this paper,the finite element model of piston rod and coating was established.Different preheating temperatures were set in piston rod.The variation laws of the residual stress and hardness were investigated.The results show that the residual stress and hardness are affected by their cooling rate.The cooling rate and the residual stress are decreased by preheating process,and it also has a significant effect on the coating hardness.With the increase of preheating temperature,the radial and axial residual stress of the piston rod and coating are decreased.Compared with the non-preheating process,the hardness of the coating basically does not change and the lower hardness of the fusion zone when the preheating temperature is 300-475 C.The hardness of coating and fusion zone is decreased significantly when the preheating temperature is 500 C.When the preheating temperature is 475 C and the same environment temperature is 20 C,the maximum radial residual stress decreases by 39.8%,the maximum axial residual stress decreases by 42.1%,and the coating hardness basically does not change with comparison of the non-preheating process.It is helpful to reduce the coating residual stress and obtain high hardness coating by preheating the piston rod to 475℃temperature before laser cladding.