本文選題：Mg-xSi合金　切入點：微觀組織　出處：《太原理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：鎂及鎂合金具有低密度、高比強度和比剛度、優(yōu)異的減震性能、杰出的阻尼性能、優(yōu)良的電磁屏蔽性能及環(huán)境友好等優(yōu)點,是最具發(fā)展前景的輕型材料之一,受到了各行各業(yè)的廣泛關(guān)注。到目前為止,高性能鎂合金廣泛應(yīng)用于航天工業(yè)、機動車、電子信息材料等領(lǐng)域。但是,高性能鎂合金的成本較高,限制了鎂合金進一步的推廣和應(yīng)用,因而開發(fā)一種成本低廉而性能優(yōu)異的鎂合金是目前材料領(lǐng)域的一個熱點課題。元素硅(Si),作為地殼中排在第二的非金屬元素,其含量豐富,價格低廉,與金屬鎂反應(yīng)生成具有高熔點、高硬度和高彈性模量的Mg_2Si相。Mg_2Si相是一種高溫強化相。通過改變Mg_2Si相在鎂合金中的形態(tài)及分布,可以顯著提高鎂合金的力學(xué)性能。本論文在含Si的Mg-Zn-Al-Mn(ZAM)系合金的研究基礎(chǔ)之上,除去Zn、Al、Mn,只在純鎂中加入元素Si,通過熔煉鑄造工藝,制備Si質(zhì)量分數(shù)分別為1%,2%,3%的Mg-xSi二元合金,并通過等通道轉(zhuǎn)角擠壓(ECAP)工藝對合金進行變形處理,以研究不同Si含量及ECAP變形對合金組織和性能的影響。Mg-xSi合金中,不同的Si含量使第二相Mg_2Si的形貌不同。Si含量為1wt.%的Mg-1Si合金中,Mg_2Si相以樹枝狀和桿狀分布在枝晶晶界上;在Si含量為2wt.%的Mg-2Si合金中,除了分布在枝晶晶界上的樹枝狀和桿狀的Mg_2Si相之外,合金組織中還分布著粗大的呈不規(guī)則多邊形塊狀的Mg_2Si相,塊狀mg2si相邊緣鋒利,對合金基體有強烈的割裂作用;當si含量為3wt.%時,即在mg-3si合金中,粗大塊狀的mg2si相體積更大,數(shù)量更多,部分mg2si相成連續(xù)帶狀分布。ecap變形能夠細化mg-xsi合金晶粒及mg2si相。ecap變形細化mg-xsi合金晶粒的機制是機械剪切破碎和連續(xù)動態(tài)再結(jié)晶。在ecap變形初期以機械剪切破碎為主,后期動態(tài)再結(jié)晶占據(jù)主導(dǎo)地位。隨著變形道次的增加,反復(fù)機械剪切和動態(tài)再結(jié)晶使合金晶粒趨于均勻細化。ecap變形能夠通過機械剪切破碎樹枝狀和桿狀的mg2si相。隨著變形道次的增加,樹枝狀和桿狀的mg2si相逐漸細化并趨于均勻彌散分布。ecap變形并不能細化粗大塊狀的mg2si相,而是隨著變形道次的增加,部分粗大塊狀的mg2si相邊緣破碎、鈍化,對合金基體的割裂作用減弱。mg-xsi合金進行室溫拉伸測試。鑄態(tài)合金中,mg-1si合金的力學(xué)性能最好,其屈服強度(ys)、抗拉強度(uts)和伸長率(elongation)分別為30mpa、93mpa和6%;ecap變形態(tài)mg-xsi合金中,mg-2si合金變形4道次后的力學(xué)性能最好,其屈服強度、抗拉強度和伸長率分別為80mpa、171mpa和13%;ecap變形能顯著提高mg-xsi合金的塑性。對于變形態(tài)mg-xsi合金,變形道次增加,合金的伸長率逐漸增大,塑性增強。si含量對合金的塑性也有一定的影響。在鑄態(tài)和ecap變形態(tài)mg-xsi合金中,si含量越高,合金的伸長率越低,塑性越差。mg-xsi合金在423k條件下進行高溫拉伸測試。鑄態(tài)合金中,mg-1si合金的力學(xué)性能最好,其屈服強度、抗拉強度和伸長率分別為23mpa、68mpa和14%。ecap變形態(tài)合金中,mg-3si合金變形2道次后的力學(xué)性能最好,其屈服強度、抗拉強度和伸長率分別為48MPa、82MPa和15%。和鑄態(tài)合金相比,1,2道次ECAP變形后的合金的屈服強度和抗拉強度有所提高,繼續(xù)增加變形道次,屈服強度和抗拉強度則降低。變形道次越多,合金在高溫下的屈服強度和抗拉強度越低。合金在高溫下的伸長率隨著變形道次的增加而顯著提升。鑄態(tài)Mg-2Si合金在448K,473K和498K條件下40~60MPa范圍內(nèi)的蠕變應(yīng)力指數(shù)分別為3.27,2.47和3.38。鑄態(tài)Mg-2Si合金40~60MPa載荷下在448K,473K和498K條件下的蠕變激活能分別為49.54139KJ·mol-1,37.39015KJ·mol-1和44.99609KJ·mol-1。在448K、473K和498K條件下,鑄態(tài)Mg-2Si合金的蠕變變形機制主要是由晶界滑移機制主導(dǎo)。
[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.

【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG146.22;TG379

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