Trial manufacture and properties of protective lubricants for hot extrusion of zirconium alloy

Lubrication is the key in obtaining excellent products when zirconium alloys are hot extruded. Reasonable lubrication conditions are important to improve the product quality, reduce energy consumption, and prolong the service life of tools and dies. Presently, the glass lubricants commonly used in domestic industry are not very suitable for hot extrusion zirconium alloy, and they still need to be imported. In order to meet the requirements of lubrication and protection during hot extrusion of zirconium alloy, a protective lubricant for hot extrusion of zirconium alloy was trial manufactured in this paper. The main components of this protective lubricant include silicone resin, low softening point glass powder, aluminum oxide (Al₂O₃) powder, molybdenum disulfide, graphite powder, talcum powder, mica powder, and others. When the experimental temperature is in the range of 700−800 ℃, the friction factor of Zr-4 alloy coated with the lubricant is calculated to be 0.19−0.25 by the ring compression method, which shows good lubrication effect. The zirconium alloy with lubricant protection is not obviously oxidized after heating at 700 ℃, 800 ℃, and 900 ℃, respectively, for 1 h, indicating that the lubricant has good thermal protection effect. The relation curves between contact temperature and time at the interface of the Zr-4 alloy and H13 die steel are measured. The initial interface temperatures of the Zr-4 alloy and H13 steel are 700 ℃ and 350 ℃, respectively. Without the lubricant, the time for the surface temperature of the Zr-4 alloy to reach stability is 7.7 s, and the interfacial heat transfer coefficient increases from 250 W·m⁻²·℃⁻¹ to 2700 W·m⁻²·℃⁻¹. On the other and, when the lubricant was used, the time for the surface temperature of Zr-4 alloy to reach stability is prolonged to 12 s, and the interfacial heat transfer coefficient increases from 131 W·m⁻²·℃⁻¹ to 1900 W·m⁻²·℃⁻¹, indicating that the lubricant has good thermal barrier properties.