基于圆环压缩和挤压–模拟法的Zr-4合金塑性成形摩擦因子测定

Measurement of friction factor in plastic forming of Zr-4 alloy based on ring compression and extrusion–simulation

采用圆环压缩法和挤压–模拟法测定Zr-4合金有润滑条件下的摩擦因子,讨论了2种方法所测定摩擦因子存在差异的原因.研究结果表明,在模具(砧面)粗糙度Ra=0.6μm、实验温度700~800℃的条件下,采用圆环压缩法获得的Zr-4合金与模具的摩擦因子为0.18~0.27,摩擦因子随实验温度的升高而增大.挤压温度为750℃时,采用挤压–模拟法获得的热挤压平均摩擦因子为0.35.测试结果存在较大差异的原因,是由于挤压过程润滑剂的剪切速率较圆环压缩实验大得多,且挤压过程中润滑剂所受压应力约为圆环压缩实验中的两倍,从而导致润滑剂黏度的增大,表现为摩擦因子较高.圆环压缩法获得的摩擦因子更适合于Zr-4合金的锻造等热加工工况.

Nuclear-grade zirconium alloys are characterized by large deformation resistance,poor fluidity,strong viscosity,and narrow forming temperature range.They are widely used in the nuclear industry and are a good choice for structural components and fuel cladding materials for nuclear power reactors.Reasonable process parameters and tooling design are very important for the production of zirconium alloy products with excellent performance.Simulation is an important technical means in plastic forming process and tool structure optimization.A prerequisite for accurate simulation is to determine precise boundary conditions,such as friction factors in plastic forming process.In this study,the friction factors under the lubrication condition of Zr-4 alloy were determined by ring compression and extrusion simulation method.The reasons for the difference in friction factors measured by the two methods were discussed.The results show that when the roughness of the die(anvil)is Ra=0.6μm and the experimental temperature is 700-800℃,the friction factor between the Zr-4 alloy and the die obtained by the ring compression is 0.18-0.27,and the friction factor increases with increasing in the experimental temperature.When the extrusion temperature is 750℃,the average friction factor of hot-extrusion obtained by extrusion simulation is 0.35.The reason for the large difference in the test results is that the shear rate of the lubricant in the extrusion process is much larger than that of the ring compression experiment,and the compressive stress of the lubricant in the extrusion process is about twice that in the ring compression experiment,which leads to an increase in the lubricant viscosity so that the friction factor is higher.The friction factor obtained by the ring compression method is more suitable for hot working conditions such as the forging of Zr-4 alloys.