等通道转角挤压（ECAP）对Mg-xSi合金组织及性能的影响

发布时间：2018-03-17 14:14

本文选题：Mg-xSi合金　切入点：微观组织　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：镁及镁合金具有低密度、高比强度和比刚度、优异的减震性能、杰出的阻尼性能、优良的电磁屏蔽性能及环境友好等优点,是最具发展前景的轻型材料之一,受到了各行各业的广泛关注。到目前为止,高性能镁合金广泛应用于航天工业、机动车、电子信息材料等领域。但是,高性能镁合金的成本较高,限制了镁合金进一步的推广和应用,因而开发一种成本低廉而性能优异的镁合金是目前材料领域的一个热点课题。元素硅(Si),作为地壳中排在第二的非金属元素,其含量丰富,价格低廉,与金属镁反应生成具有高熔点、高硬度和高弹性模量的Mg_2Si相。Mg_2Si相是一种高温强化相。通过改变Mg_2Si相在镁合金中的形态及分布,可以显著提高镁合金的力学性能。本论文在含Si的Mg-Zn-Al-Mn(ZAM)系合金的研究基础之上,除去Zn、Al、Mn,只在纯镁中加入元素Si,通过熔炼铸造工艺,制备Si质量分数分别为1%,2%,3%的Mg-xSi二元合金,并通过等通道转角挤压(ECAP)工艺对合金进行变形处理,以研究不同Si含量及ECAP变形对合金组织和性能的影响。Mg-xSi合金中,不同的Si含量使第二相Mg_2Si的形貌不同。Si含量为1wt.%的Mg-1Si合金中,Mg_2Si相以树枝状和杆状分布在枝晶晶界上;在Si含量为2wt.%的Mg-2Si合金中,除了分布在枝晶晶界上的树枝状和杆状的Mg_2Si相之外,合金组织中还分布着粗大的呈不规则多边形块状的Mg_2Si相,块状mg2si相边缘锋利,对合金基体有强烈的割裂作用;当si含量为3wt.%时,即在mg-3si合金中,粗大块状的mg2si相体积更大,数量更多,部分mg2si相成连续带状分布。ecap变形能够细化mg-xsi合金晶粒及mg2si相。ecap变形细化mg-xsi合金晶粒的机制是机械剪切破碎和连续动态再结晶。在ecap变形初期以机械剪切破碎为主,后期动态再结晶占据主导地位。随着变形道次的增加,反复机械剪切和动态再结晶使合金晶粒趋于均匀细化。ecap变形能够通过机械剪切破碎树枝状和杆状的mg2si相。随着变形道次的增加,树枝状和杆状的mg2si相逐渐细化并趋于均匀弥散分布。ecap变形并不能细化粗大块状的mg2si相,而是随着变形道次的增加,部分粗大块状的mg2si相边缘破碎、钝化,对合金基体的割裂作用减弱。mg-xsi合金进行室温拉伸测试。铸态合金中,mg-1si合金的力学性能最好,其屈服强度(ys)、抗拉强度(uts)和伸长率(elongation)分别为30mpa、93mpa和6%;ecap变形态mg-xsi合金中,mg-2si合金变形4道次后的力学性能最好,其屈服强度、抗拉强度和伸长率分别为80mpa、171mpa和13%;ecap变形能显著提高mg-xsi合金的塑性。对于变形态mg-xsi合金,变形道次增加,合金的伸长率逐渐增大,塑性增强。si含量对合金的塑性也有一定的影响。在铸态和ecap变形态mg-xsi合金中,si含量越高,合金的伸长率越低,塑性越差。mg-xsi合金在423k条件下进行高温拉伸测试。铸态合金中,mg-1si合金的力学性能最好,其屈服强度、抗拉强度和伸长率分别为23mpa、68mpa和14%。ecap变形态合金中,mg-3si合金变形2道次后的力学性能最好,其屈服强度、抗拉强度和伸长率分别为48MPa、82MPa和15%。和铸态合金相比,1,2道次ECAP变形后的合金的屈服强度和抗拉强度有所提高,继续增加变形道次,屈服强度和抗拉强度则降低。变形道次越多,合金在高温下的屈服强度和抗拉强度越低。合金在高温下的伸长率随着变形道次的增加而显著提升。铸态Mg-2Si合金在448K,473K和498K条件下40~60MPa范围内的蠕变应力指数分别为3.27,2.47和3.38。铸态Mg-2Si合金40~60MPa载荷下在448K,473K和498K条件下的蠕变激活能分别为49.54139KJ·mol-1,37.39015KJ·mol-1和44.99609KJ·mol-1。在448K、473K和498K条件下,铸态Mg-2Si合金的蠕变变形机制主要是由晶界滑移机制主导。
[Abstract]:Magnesium and magnesium alloys have low density, high specific strength and stiffness, excellent damping performance, excellent damping performance, electromagnetic shielding performance and environmentally friendly advantages such as excellent, is one of the most promising light-weight materials, has attracted wide attention from all walks of life. So far, high performance magnesium alloy is widely used in the aerospace industry, motor vehicles, the field of electronic information materials. However, the high cost of high performance magnesium alloy, limits the popularization and application of magnesium alloy further, thus the development of a low cost and excellent performance of magnesium alloy is a hot topic in the field of materials. The silicon element (Si), as the crust came in second non metallic elements, its content is rich, the price is low, reacted with magnesium to generate high melting point, high hardness and high elastic modulus Mg_2Si of.Mg_2Si phase is a high temperature strengthening phase. By changing the Mg_2Si phase in mg The morphology and distribution of alloy, can significantly improve the mechanical properties of magnesium alloy. In this paper, including Si Mg-Zn-Al-Mn (ZAM) on the basis of alloy removal of Zn, Al, Mn, Si elements added only in pure magnesium, by melting casting process, the preparation of Si mass fraction were 1%, 2% 3%, the Mg-xSi two alloy by equal channel angular extrusion (ECAP) process on alloy deformation processing, with different content of Si and ECAP on the deformation effect of.Mg-xSi alloy on Microstructure and mechanical properties, morphology of different content of.Si second phase Mg_2Si Si with different content of Mg-1Si alloy 1wt.%, Mg_2Si the dendritic and rod-shaped distribution in dendrite boundaries; in the Si content of Mg-2Si alloy 2wt.%, in addition to the distribution in the dendrite boundaries of dendrimers and rod like Mg_2Si phase in the alloy, but also the distribution of coarse and irregular polygonal blocky Mg_2Si phase, Blocky Mg2Si phase sharp edges, there are separate function of alloy substrate; when the Si content is 3wt.%, which is in the mg-3si alloy, thick massive Mg2Si phase is larger and more, part of the Mg2Si phase continuous zonal distribution of.Ecap deformation can be deformation mechanism of grain refinement in mg-xsi alloy.Ecap phase on grain refinement in mg-xsi alloy and Mg2Si mechanical shear fracture and continuous dynamic recrystallization in ECAP. At the beginning of deformation by mechanical shear fracture, post dynamic recrystallization dominates. With the increasing of deforming cycles of repeated mechanical shear and dynamic recrystallization of the alloy grain refinement of.Ecap uniform deformation can be broken by mechanical shear dendrimers and rod like Mg2Si phase with. The deformation times increasing, dendritic and rod like Mg2Si phase gradually refine and uniform dispersed.Ecap deformation can not be refined and thick massive Mg2Si phase, but with the With the increase of deformation time, part of the coarse Mg2Si phase block edge broken, passivation, fragmentation effect to alloy matrix weakened.Mg-xsi alloy tensile testing. In the as cast alloy, the mechanical properties of mg-1si alloy is the best, its yield strength (YS), tensile strength (UTS) and elongation (elongation) were 30MPa 93mpa and ECAP, 6%; changed configuration of mg-xsi alloy, mg-2si alloy mechanical properties after 4 passes of the best, its yield strength, tensile strength and elongation were 80MPa and 171mpa, 13%; ECAP can significantly improve the plastic deformation of mg-xsi alloy. The morphology change of mg-xsi alloy, deformation times, alloy the plastic elongation increases, increasing the content of.Si on ductility of the alloy has a certain impact. In the as cast and ECAP morphology of mg-xsi alloy, the content of Si is higher, the elongation of the alloy is lower, the worse the plastic.Mg-xsi alloy in high 423K conditions The temperature tensile test. The as cast alloy, the mechanical properties of mg-1si alloy is the best, its yield strength, tensile strength and elongation were 23mpa, 68mpa and 14%.ecap form alloy, mg-3si alloy mechanical properties after 2 passes of the best, its yield strength, tensile strength and elongation were 48MPa, compared to 82MPa and 15%. and as cast alloy, alloy 1,2 ECAP after deformation of the yield strength and tensile strength increased, continue to increase the deformation, yield strength and tensile strength decreased. Deformation times more alloy at high temperature the yield strength and tensile strength of lower elongation. In high temperature alloy significantly enhance with the increasing of deforming cycles. As cast Mg-2Si alloy in 448K, creep of 40~60MPa in the range of 473K and 498K under the condition of stress index were 3.27,2.47 and 3.38. cast Mg-2Si alloy under the loading of 40~60MPa in 448K, 473K and 498K Under the condition of 448K, 473K and 498K, the activation energy of creep under 49.54139KJ, mol-1,37.39015KJ, mol-1 and 44.99609KJ / mol-1. is mainly dominated by grain boundary sliding mechanism.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22;TG379

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