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

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 = 0.6 μm 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.