發(fā)布時(shí)間：2018-06-08 11:06

  本文選題：Mg-Zn-Y合金 + 定向凝固��； 參考：《太原科技大學(xué)》2017年碩士論文

【摘要】：目前,采用普通凝固技術(shù)獲得的鎂合金室溫、高溫力學(xué)性能,蠕變抗力,導(dǎo)熱、導(dǎo)電等性能往往難以滿足性能需求,而定向凝固作為一種新型凝固技術(shù),通過(guò)控制單向熱流獲得單向凝固組織,可以提高鎂合金各項(xiàng)性能。本文設(shè)計(jì)并制備了高導(dǎo)熱、高比強(qiáng)的Mg-xZn-Y(x=1、3、5wt.%)合金,通過(guò)定向凝固裝置、光學(xué)顯微鏡、掃描電鏡、XRD衍射儀、材料試驗(yàn)機(jī)以及硬度計(jì)等設(shè)備來(lái)研究鑄態(tài)和定向凝固工藝下Mg-Zn-Y合金力學(xué)性能和導(dǎo)熱性能的變化規(guī)律以及影響機(jī)理,設(shè)置定向凝固參數(shù)為:溫度梯度70 K/cm、100 K/cm;生長(zhǎng)速度5μm/s、10μm/s、25μm/s、50μm/s、100μm/s。通過(guò)研究得出以下結(jié)論:(1)Mg-xZn-Y合金組織主要由α-Mg基體相與第二相W相、I相組成,基體相呈花瓣?duì)畹牡容S晶,第二相呈白色粒狀彌散分布于基體或晶界上。定向凝固能夠使鑄態(tài)合金組織由等軸晶向柱狀晶演化轉(zhuǎn)變,與鑄態(tài)組織相比,沉淀析出的第二相數(shù)量增多。(2)鑄態(tài)條件下,Zn可以細(xì)化合金組織,當(dāng)Zn含量增大時(shí),晶粒細(xì)化,沉淀析出第二相數(shù)量增多,分布也更加均勻。定向凝固條件下,當(dāng)生長(zhǎng)速度恒定時(shí),溫度梯度增大,柱狀晶更粗大、均勻、方向性也更好;當(dāng)溫度梯度恒定時(shí),生長(zhǎng)速度增大,柱狀晶平均寬度逐漸變窄,晶粒分布的均勻性逐漸降低,晶粒生長(zhǎng)的方向性、連續(xù)性也逐漸變差。(3)定向凝固條件下,當(dāng)生長(zhǎng)速度恒定時(shí),溫度梯度增大,抗拉強(qiáng)度、伸長(zhǎng)率和硬度都呈現(xiàn)出增大的趨勢(shì),通過(guò)對(duì)比發(fā)現(xiàn),高溫度梯度下的抗拉強(qiáng)度較之低溫度梯度下的抗拉強(qiáng)度提高了約9.3%,伸長(zhǎng)率提高了約15.0%,合金硬度提高了約11.3%;當(dāng)溫度梯度一定,生長(zhǎng)速度逐漸增大時(shí),抗拉強(qiáng)度、伸長(zhǎng)率和硬度呈現(xiàn)出先增后降的趨勢(shì),當(dāng)溫度梯度在100 K/cm,生長(zhǎng)速度達(dá)到50μm/s時(shí),抗拉強(qiáng)度、伸長(zhǎng)率、硬度達(dá)到了最大值,分別為245.0 MPa、13.3%、71.7 HV,相比于鑄態(tài)合金,分別提高了35.7%、49.4%,26.0%。(4)當(dāng)Zn含量在(1~5 wt.%)范圍內(nèi)增大時(shí),鑄態(tài)合金熱導(dǎo)率降低,并且,Zn含量的增大對(duì)熱導(dǎo)率的影響十分明顯,呈線性下降趨勢(shì)。定向凝固條件下,當(dāng)生長(zhǎng)速度恒定時(shí),溫度梯度增大,合金的熱導(dǎo)率呈現(xiàn)小幅增長(zhǎng)的趨勢(shì);當(dāng)溫度梯度恒定時(shí),生長(zhǎng)速度增大,熱導(dǎo)率呈現(xiàn)逐漸下降的趨勢(shì)。但是,相比于鑄態(tài)合金,定向凝固合金的熱導(dǎo)率均有所提高。以Mg-3Zn-Y合金為例,當(dāng)溫度梯度為100 K/cm,生長(zhǎng)速度為5μm/s時(shí),合金的熱導(dǎo)率最高達(dá)到了149.73 W/(m?K),比鑄態(tài)合金提高了36.0%;當(dāng)溫度梯度為100 K/cm,生長(zhǎng)速度為100μm/s時(shí),定向凝固熱導(dǎo)率最低為128.64 W/(m?K),比鑄態(tài)合金提高了13.1%。
[Abstract]:At present, the mechanical properties, creep resistance, thermal conductivity and electrical conductivity of magnesium alloys obtained by ordinary solidification technology are often difficult to meet the requirements of performance, and directional solidification is a new solidification technology. The properties of magnesium alloy can be improved by controlling unidirectional heat flux to obtain unidirectional solidified microstructure. In this paper, a high thermal conductivity and high specific strength Mg-xZn-YTX (1) -5 wt.alloy was designed and prepared. The alloy was characterized by directional solidification, optical microscope, scanning electron microscopy and XRD diffraction. The mechanical properties and thermal conductivity of Mg-Zn-Y alloy under as-cast and directional solidification conditions were studied by material testing machine and hardness tester. The directional solidification parameters were set as follows: temperature gradient 70 K / cm ~ (100) K / cm; growth rate 5 渭 m / s ~ (10) 渭 m / s ~ (25) 渭 m / s ~ (50) 渭 m 路s ~ (-1) ~ 100 渭 m 路s ~ (-1). It is concluded that the microstructure of the alloy consists of 偽 -Mg matrix phase and the second phase W phase I phase, the matrix phase is petal-like equiaxed crystal, the second phase is white granular dispersion on the matrix or grain boundary. Directional solidification can change the structure of as-cast alloy from equiaxed to columnar. Compared with the as-cast structure, the amount of the second phase precipitated by precipitation can be increased under the condition of as-cast. Zn can refine the microstructure of the alloy, and when Zn content increases, the grain size will be refined. The number of precipitated second phases increased and the distribution was more uniform. Under the condition of directional solidification, when the growth rate is constant, the temperature gradient increases, the columnar crystal is thicker, uniform, and the directivity is better, and when the temperature gradient is constant, the growth rate increases and the average width of columnar crystal becomes narrower. Under the condition of directional solidification, when the growth rate is constant, the temperature gradient increases and the tensile strength, elongation and hardness increase. It is found by comparison that tensile strength at high temperature gradient is about 9.3% higher than that at low temperature gradient, elongation increases 15.0%, hardness of alloy increases about 11.3%, tensile strength increases gradually when temperature gradient is constant and growth rate increases gradually. The elongation and hardness increased first and then decreased. When the temperature gradient was 100K / cm and the growth rate was 50 渭 m / s, the tensile strength, elongation and hardness of the alloy reached the maximum value, which were 245.0 MPA / 13.3 and 71.7HVrespectively, compared with the as-cast alloy. The thermal conductivity of as-cast alloys decreased with the increase of Zn content in the range of 1wt.) and the effect of Zn content on the thermal conductivity was obvious, which showed a linear decreasing trend. Under the condition of directional solidification, when the growth rate is constant, the temperature gradient increases, the thermal conductivity of the alloy increases slightly, and when the temperature gradient is constant, the growth rate increases and the thermal conductivity decreases gradually. However, compared with the as-cast alloy, the thermal conductivity of the directionally solidified alloy is improved. Taking Mg-3Zn-Y alloy as an example, when the temperature gradient is 100K / cm and the growth rate is 5 渭 m / s, the thermal conductivity of the alloy reaches the highest level of 149.73 W / m ~ (-1), which is 36.0% higher than that of the as-cast alloy, and when the temperature gradient is 100 K / cm and the growth rate is 100 渭 m / s, the thermal conductivity of Mg-3Zn-Y alloy is 36.0% higher than that of the as-cast alloy. The lowest thermal conductivity of directional solidification is 128.64 W / m ~ (-1), which is 13.1% higher than that of as-cast alloy.
【學(xué)位授予單位】：太原科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG146.22;TG292

【參考文獻(xiàn)】

相關(guān)期刊論文 前10條

1 游國(guó)強(qiáng);白世磊;明s，

本文編號(hào)：1995582