为了开发新的弯管件加工工艺,提出了一种动态调整传统分流挤压模具中分流孔内金属流量(dynamic flow con-trol extrusion,DFCE)的挤压变形方法.在带有辅助调控挤压杆的630 T卧式挤压机上挤出镁合金弯管件,采用OM、SEM、TEM、拉伸试验等方法,研究了DFCE制造的镁合金弯管件的晶粒细化方式、微观组织结构和性能.结果表明:在变形温度450℃、直管挤压速度3 mm/s、弯管挤压速度1.5 mm/s、辅助调控挤压杆速度30 mm/s时,成功挤出变形均匀的弯管件;挤压后的直管部分和弯管部分的晶粒尺寸分别为7.9和12.8μm,且合金晶粒大小均匀;弯管部分室温拉伸强度和屈服强度分别由217和124 MPa提高到296和179 MPa,延伸率由12.9%提高到26.2%.DFCE挤压变形可以显著细化AZ91镁合金晶粒,其挤压过程中晶粒细化机制为位错驱动和动态再结晶,机械性能较铸态大幅度提高,坯料和挤出合金的拉伸断口分别呈现为准解理断裂和韧窝断裂的特征.
To develop a new processing technology of bent pipe, a deformation technique of the dynamic flow control extrusion ( DFCE ) was proposed. The magnesium alloy bending tube processed on 630T horizontal extrusion equipment with auxiliary ram. Microstructure and mechanical properties of DFCEed magnesium alloy tube were studied by using optical microscopy ( OM ) , scanning electron microscopy ( SEM ) , transmission electron microscopy ( TEM) and tensile tests. The results show that metal flow is uniform at the temperature of 450℃ and an extrusion rate of 3 mm/s for straight pipe and an extrusion rate of 3 mm/s for bent pipe. The mean grain sizes of straight pipe and bent pipe after extrusion are 7. 9 μm and 12. 8 μm, respectively. The mechanical properties are greatly improved. The tensile strength, yield strength and elongation of the straight pipe tube sample increase from 217 MPa, 124 MPa and 12.9%to 296 MPa, 179 MPa and 26.2%, respectively. The DFCE could significantly refine the grains of the AZ91 magnesium alloy, which can be attributed to the multiplication of dislocation and dynamic recrystallization. Quasi-cleavage fracture and dimple fracture dominate the tensile fracture morphology of the billet and the DFCEed alloy, respectively.
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