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Title:: Effect of Strain Rates on Rotary Backward Extrusion of Mg-13Gd-4Y-2Zn-0.5Zr Magnesium Alloy

作者:: 屈曉曉1; 張治民1; 于建民1; 房慶齡1; 劉濤2; 1. 中北大學材料科學與工程學院，山西太原 030000 2. 裝甲軍代局駐太原地區軍代室，山西太原 030006

Author(s):: QU Xiaoxiao1; ZHANG Zhimin1; YU Jianmin1; FANG Qingling1; LIU Tao2; (1. School of Materials Science and Engineering, North University of China）
(2. Taiyuan Military Representative Office of Armored Military Representative Bureau）

Keywords:: Mg-Gd-Y-Zn-Zr magnesium alloy; rotary backward extrusion; strain rate; microstructures; Vickers hardness

摘要:: 旋轉反擠壓是一種將旋轉運動和正常反擠壓運動相結合的塑性成形新方法，可以實現Mg-13Gd-4Y-2Zn-0.5Zr鎂合金的劇烈塑性變形，改善其組織和性能。以旋轉擠壓為工藝對象，利用Gleeble3500熱模擬機研究了鎂合金杯形件成形過程中應變速率對材料組織和性能的影響規律。結果表明：Mg-13Gd-4Y-2Zn-0.5Zr鎂合金杯形件旋轉反擠壓過程中，顯微硬度分布較為均勻，試樣從外部到內部的晶粒逐漸細化，沿旋轉方向動態再結晶程度逐漸提高，晶粒尺寸逐漸減小。在周向應變速率周從0增大到0.05 s-1的過程中，動態再結晶晶粒的占比逐漸上升，在周為0.005 s-1時，片狀LPSO相的破碎使此時材料的硬度提高，并抑制了動態再結晶晶粒的產生。周的繼續增加使位錯密度增大，促進了動態再結晶。在旋轉反擠壓進行過程中，隨時間的增加成形載荷波動上升，且隨著周的增加，成形載荷逐漸下降。

Abstract:: Rotating back extrusion is a new forming method which combines rotational motion with common reverse extrusion. It can realize a severe plastic deformation of Mg-13Gd-4Y-2Zn-0.5Zr
magnesium alloy and improve its microstructure and properties. Based on rotating back extrusion, the influence of the strain rate on microstructure and properties during the forming process of magnesium alloy cup are studied by using Gleeble3500 thermal simulator. The results show that in the process of rotating back extrusion of Mg-13Gd-4Y-2Zn-0.5Zr
magnesium alloy cup, the microhardness distribution of the magnesium alloy becomes more uniform, the grain size inside the sample gets thinner than the outside, the dynamic recrystallization degree increases gradually along the rotation direction and the grain size gradually decreases. As the strain rate increases from 0 s-1 to 0.05 s-1, the proportion of dynamic recrystallized grains increases. When the strain rate is 0.05 s-1, the sheet LPSO phases begin to break up, which makes the hardness of the material increases and inhibits the generation of dynamically recrystallized grain. With the strain rate keeping on raising, the dislocation density increases, which promotes dynamic recrystallization. During the process of rotating backward extrusion, the fluctuation of the forming load increases with time, and the forming load gradually decreases with the raising of strain rate.