合金元素对镁合金临界剪切应力与力学行为影响的研究

发布时间：2018-07-18 21:08

【摘要】：镁合金因其质轻、比强度高、阻尼减振和电磁屏蔽性能好等优点受到越来越多的关注。变形镁合金在室温下非基面与基面滑移的临界剪切应力(CRSS)比值较大,室温独立滑移系少,导致变形镁合金,特别是镁合金板材的室温成形性能较差,这严重制约了变形镁合金的发展。合金元素改性可有效降低镁合金非基面/基面滑移的CRSS比值,从而改善变形镁合金的成形性能。本文利用第一性原理计算研究典型合金元素对镁晶体理论临界剪切强度(τmax)的影响,制备出相应的镁合金材料;采用金相分析(OM)、扫描电镜(SEM)、X射线衍射(XRD)、电子背散射衍射(EBSD)和力学性能测试等手段考察这些镁合金在不同塑性变形工艺下的显微组织及力学行为的演变。研究结果表明:①溶质原子Li、Sn与Y在镁晶体中优先固溶于}0211{面。单位原子的合金元素减小镁非基面/基面τmax比值顺序为:SnLiY;单位质量的合金元素减小其非基面/基面τmax比值顺序为:LiSnY。②对于Mg-Li二元挤压板材,随着Li含量的增加,合金晶粒取向发生改变,从Mg-(1-2)Li合金的基面取向逐渐向Mg-3Li合金的非基面取向演变,且Mg-3Li合金的延伸率、加工硬化指数n值及强度均明显提高,板材经30%的轧制变形后,各向异性得到了进一步改善。③在不同变形量的室温轧制下,Mg-x Li-3Al-1Zn(LAZx31,x=1,3,5;wt.%)挤压板材表现出不同的塑性变形模式:LAZ131在整个轧制变形过程中均以基面滑移和孪生为主;LAZ331在5%轧制变形下主要发生柱面滑移与}2211{锥面滑移,10%时主要发生}2101{拉伸孪生与}2211{锥面滑移,15%时主要发生}2101{拉伸孪生与}1101{压缩孪生,20%时主要发生}1101{压缩孪生与}1101{-}2110{二次孪生;LAZ531在5%轧制变形下主要发生}0211{柱面滑移及锥面滑移,10%与15%时主要发生}2110{拉伸孪生与锥面滑移,20%时主要发生}2110{拉伸孪生与}1101{压缩孪生。④Sn元素固溶可以改善纯镁的室温成形性能,当Sn在Mg中的固溶量为2.5wt.%时,合金的成形性能最佳,铸态合金的室温轧制压下量可达到22.6%。随着Sn含量增加,挤压态Mg-Sn合金的抗拉强度、延伸率及加工硬化指数n值均呈升高的趋势。⑤Mg-0.5Sn-0.3Y合金挤压板材晶粒尺寸比Mg-0.5Sn合金挤压板材细化约77%,沿ED、45o和TD三个方向的延伸率分别为30.3%、28.1%和28%,抗拉强度分别为288MPa、286MPa和302MPa,且各向异性不明显。Mg-0.5Sn-0.3Y挤压板材的显微组织与力学性能得到改善的主要原因在于:Sn3Y5颗粒在再结晶过程中的晶粒细化作用导致板材晶粒尺寸只有约4μm;在镁基体中固溶的Sn与Y均能降低镁基体非基面与基面的CRSS比值,促进非基面滑移,从而改善合金塑性。
[Abstract]:Magnesium alloys have attracted more and more attention because of their advantages of light weight, high specific strength, good damping and electromagnetic shielding. At room temperature, the critical shear stress (CRSS) ratio of non-basal and basal slip of wrought magnesium alloy is larger, and the independent slip system is less at room temperature, which results in poor room temperature formability of wrought magnesium alloy, especially magnesium alloy sheet. This seriously restricts the development of wrought magnesium alloys. The alloy element modification can effectively reduce the CRSS ratio of non-basal / basal slip of magnesium alloy and improve the formability of wrought magnesium alloy. In this paper, the influence of typical alloy elements on the theoretical critical shear strength (蟿 max) of magnesium crystals was studied by first principle calculation, and the corresponding magnesium alloy materials were prepared. Metallographic analysis (OM), scanning electron microscopy (SEM) X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and mechanical properties were used to investigate the evolution of microstructure and mechanical behavior of these magnesium alloys under different plastic deformation conditions. The results show that Li _ (Sn) Sn and Y are the preferred solid solution in magnesium crystal at 0211 {plane. For Mg-Li binary extruded sheet, the order of decreasing mg non-basal / basal 蟿 max ratio of unit atom is: SnLiY, and that of unit mass alloy element decreasing is: 1: LiSnY.2 for Mg-Li binary extruded sheet, the order is: 1. 0% LiSnY.2 for Mg-Li binary extruded sheet, with the increase of Li content, the order is: 1% LiSnY.2 for Mg-Li binary extruded sheet. The grain orientation of Mg-3Li alloy changed gradually from the base orientation of Mg- (1-2) Li alloy to the non-basal orientation of Mg-3Li alloy, and the elongation, work hardening index n value and strength of Mg-3Li alloy increased obviously, and the plate was deformed by 30% rolling. Anisotropy is further improved at room temperature rolling of Mg-x Li-3Al-1Zn (LAZx31HX) extruded sheet with different plastic deformation modes: 1: LAZ131 during the whole rolling process, the base plane slip and twinning are dominant in the 5% rolling process. Under deformation, cylinder slip and} 2211 {cone slip occur mainly,} 2101 {tensile twin and} 2211 {cone slip occur mainly at 10,} 2101 {tensile twin and} 1101 {compressed twin at 15,} 1101 {compressed twin and} 1101 {-} 2110 {double twin LAZ531 in 20s. Under 5% rolling deformation,} 0211 {cylinder slip and cone slip 10% and 15%,} 2110 {tensile twinning and cone slip,} 2110 {tensile twin and} 1101 {compression twin. 4Sn solution can improve the room temperature formability of pure magnesium. When the solid solution of Sn in mg is 2.5 wt.%, the formability of the alloy is the best, and the rolling reduction of as-cast alloy at room temperature can reach 22.6. The tensile strength of the extruded Mg-Sn alloy increases with the increase of Sn content. The grain size of 5Mg-0.5Sn-0.3Y alloy extruded sheet is about 77cm than that of Mg-0.5Sn alloy extruded sheet. The elongation along EDG45o and TD three directions are 30.3% and 28.1%, respectively. The tensile strength is 288MPa 286MPa, respectively. The main reason for the improvement of the microstructure and mechanical properties of the extruded sheet with 302MPa and 302MPA, and the anisotropy is not obvious. The main reason for the improvement of the microstructure and mechanical properties of the extruded sheet is that the grain size of the sheet is only about 4 渭 m due to the effect of grain refinement of the W Sn3Y5 particles during recrystallization; in magnesium matrix, the grain size is only about 4 渭 m. Both Sn and Y solution can reduce the CRSS ratio of non-base and base surface of magnesium matrix. Promote non-base slip, thereby improving the alloy plasticity.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.22

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