热挤压高强TiCp/Mg-1.4Zn-2.6Ca-0.5Mn纳米复合材料的组织与力学性能

Microstructure and mechanical properties of ultra-high strength TiCp/Mg-1.4Zn-2.6Ca-0.5Mn nanocomposite after hot extrusion

采用超声波辅助半固态搅拌铸造法制备TiCp/Mg-1.4Zn-2.6Ca-0.5Mn纳米复合材料,实现纳米TiCp的均匀分布,并分析热挤压前后复合材料的组织与力学性能。结果表明:挤压前第二相密集区晶粒尺寸小于第二相贫瘠区,第二相为Ca2Mg6Zn3相;不同温度(350℃、310℃和270℃)挤压后复合材料均发生了动态再结晶(DRX),随挤压温度的降低,DRX晶粒尺寸及其体积分数趋于减小,而析出相体积分数则略有增加,超细晶(约0.34μm)和大量MgZn2析出相出现在270℃挤压态复合材料中;复合材料晶粒细化不仅与DRX有关,还与纳米级的α-Mn颗粒、TiCp和MgZn2析出相的钉扎效应有关;经270℃/0.1 mm•s−1挤压后,复合材料的屈服强度(YS)、极限抗拉强度(UTS)和伸长率(EL)分别约为439.7 MPa、460.2 MPa和1.73%;屈服强度提高主要与细晶强化、Orowan强化、热错配强化和位错强化有关,其中细晶强化的贡献率最大超过60%。

A uniform distribution of TiCp nanoparticles was realized in the TiCp/Mg-1.4Zn-2.6Ca-0.5Mn nanocomposite fabricated by the method of ultrasonic-assisted semisolid stirring.Microstructure and mechanical properties of the nanocomposite before and after extrusion were investigated.The results show that the grains in the dense area of the second phase were smaller than those in the barren area,and the second phase was Ca2Mg6Zn3.Dynamic recrystallization(DRX)occurred in the nanocomposites after extrusion at different temperatures(350°C,310°C and 270°C).Both the sizes and volume fraction of DRX grains and precipitates size were obviously refined as the extrusion temperature decreased,while the volume fraction of precipitates increased.Ultrafine recrystallized grain structure(≈0.34μm)with a substantial of fine precipitates appeared in the nanocomposite extruded at 270°C.The refined grain structure was not only due to DRX,but also the synergistic pinning effect of nano-TiCp,precipitated MgZn2 andα-Mn particles.The optimum tensile strength was achieved in the nanocomposites extruded at 270°C/0.1 mm•s–1,and the yield strength(YS),ultimate tensile strength(UTS)and elongation to failure(EL)were≈439.7 MPa、≈460.2 MPa and≈1.73%,respectively.The grain refinement strengthening with the contribution ratio over 60%to YS increment was much higher relative to thermal expansion effect,Orowan strengthening and dislocation strengthening.