Mg-Zn-Y-Zr合金攪拌摩擦加工組織演變機(jī)理及強(qiáng)韌化研究
發(fā)布時(shí)間：2019-05-18 07:53
【摘要】：稀土鎂合金相比于傳統(tǒng)鎂合金,具有高強(qiáng)度、耐高溫和耐腐蝕等特點(diǎn),在輕量化領(lǐng)域具有十分廣闊的應(yīng)用前景。目前稀土鎂合金制備以鑄造為主,提高其強(qiáng)度和塑性是當(dāng)前推廣鎂合金使用的重要課題之一。攪拌摩擦加工作為一種大塑性變形技術(shù),具有操作簡(jiǎn)便、高效和環(huán)保等優(yōu)點(diǎn),可實(shí)現(xiàn)材料的局部或整體改性,提高材料的服役性能。本文對(duì)攪拌摩擦加工制備高性能Mg-Zn-Y-Zr合金進(jìn)行了研究,闡述了攪拌摩擦加工參數(shù)和材料初始狀態(tài)對(duì)攪拌摩擦加工區(qū)域鎂合金宏微觀(guān)組織、力學(xué)性能和斷裂行為的影響,分析了攪拌摩擦加工材料的時(shí)效析出行為及其對(duì)力學(xué)性能的影響,揭示了攪拌摩擦加工強(qiáng)韌化鎂合金材料的內(nèi)在機(jī)制,并實(shí)現(xiàn)了高強(qiáng)高韌鎂合金的制備。對(duì)鑄態(tài)Mg-Zn-Y-Zr合金進(jìn)行攪拌摩擦加工,通過(guò)改變行進(jìn)速度研究不同程度熱機(jī)耦合作用對(duì)鑄態(tài)粗晶鎂合金的組織改善和性能提升效果。攪拌摩擦加工后,攪拌區(qū)分為上部呈現(xiàn)纖維狀晶粒的纖維區(qū)和中下部呈現(xiàn)細(xì)小等軸晶的細(xì)晶區(qū),隨著行進(jìn)速度的提高,細(xì)晶區(qū)面積逐漸減小,但減小速率快速下降。攪拌摩擦加工后鎂合金組織顯著細(xì)化,鑄態(tài)粗晶發(fā)生劇烈的動(dòng)態(tài)再結(jié)晶,晶粒細(xì)化至微米級(jí)別,鑄態(tài)組織中粗大的晶間網(wǎng)狀共晶相破碎成細(xì)小顆粒并彌散分布。在劇烈的熱機(jī)耦合作用下,材料的元素?cái)U(kuò)散速率大幅提升,使被破碎的I相(Mg3Zn6Y)顆�？焖俎D(zhuǎn)變?yōu)閃相(Mg3Zn3Y2)顆粒,形成芯部為殘余I相,邊緣為W相的芯殼結(jié)構(gòu)。攪拌摩擦加工過(guò)程中劇烈的塑性變形使細(xì)晶區(qū)形成鎂基面平行于攪拌針表面的環(huán)形基面織構(gòu)。細(xì)晶、彌散顆粒和環(huán)形基面織構(gòu)均有利于材料強(qiáng)度和塑性的提升。隨著行進(jìn)速度的提高,細(xì)晶區(qū)中晶粒尺寸減小,彌散顆粒含量提高,整體力學(xué)性能提升,在800 rpm-200 mm/min工藝參數(shù)下屈服強(qiáng)度、抗拉強(qiáng)度和延伸率分別達(dá)到171MPa、300 MPa和27%,相比于鑄態(tài)母材分別提高了92%,53%和145%。對(duì)鑄態(tài)和固溶態(tài)合金攪拌摩擦加工的熱機(jī)影響區(qū)進(jìn)行組織分析,表征不同部位微區(qū)組織特征研究攪拌摩擦加工過(guò)程中的微觀(guān)組織演變行為,隨著攪拌摩擦加工過(guò)程中熱機(jī)耦合作用的增強(qiáng),粗晶鎂合金中先后發(fā)生孿生動(dòng)態(tài)再結(jié)晶、顆粒促進(jìn)形核以及連續(xù)和不連續(xù)動(dòng)態(tài)再結(jié)晶從而使晶粒細(xì)化。由于固溶態(tài)合金內(nèi)第二相含量較少,且大量固溶原子造成溶質(zhì)拖曳效應(yīng)顯著降低動(dòng)態(tài)再結(jié)晶程度,使固溶態(tài)合金攪拌摩擦加工細(xì)晶區(qū)材料的平均晶粒尺寸偏大,強(qiáng)度低于相同參數(shù)下的鑄態(tài)攪拌摩擦加工細(xì)晶區(qū)材料。對(duì)于800 rpm-200 mm/min工藝參數(shù)下的鑄態(tài)和固溶態(tài)合金攪拌摩擦加工細(xì)晶區(qū)材料,250℃下分別時(shí)效處理8 h和10 h可達(dá)峰時(shí)效狀態(tài)。由于大量熱穩(wěn)定性良好的W相彌散顆粒和沿晶界析出W相納米顆粒的阻礙作用,晶粒長(zhǎng)大緩慢,在峰時(shí)效狀態(tài)下仍保持微米級(jí)細(xì)晶組織。峰時(shí)效下在晶粒內(nèi)部析出β1'桿狀沉淀相,進(jìn)一步提高材料的強(qiáng)度且保持較高的塑性。鑄態(tài)合金攪拌摩擦加工細(xì)晶區(qū)峰時(shí)效材料的屈服強(qiáng)度、抗拉強(qiáng)度和延伸率分別達(dá)到201 MPa、330 MPa和24%,較鑄態(tài)母材分別提高了126%、68%和118%,實(shí)現(xiàn)了高強(qiáng)高韌鎂合金的制備。
[Abstract]:Compared with the traditional magnesium alloy, the rare earth magnesium alloy has the characteristics of high strength, high temperature resistance and corrosion resistance and the like, and has a wide application prospect in the field of light weight. At present, the preparation of rare-earth magnesium alloy is dominated by casting, and the strength and plasticity of the rare-earth magnesium alloy are one of the most important topics to be used to promote the use of the magnesium alloy. The stirring and friction processing is used as a large plastic deformation technology, and has the advantages of simple and convenient operation, high efficiency, environmental protection and the like, and can realize the local or integral modification of the material and improve the service performance of the material. In this paper, a high-performance Mg-Zn-Y-Zr alloy was prepared by friction stir processing, and the effects of the friction processing parameters and the initial state of the material on the microstructure, mechanical properties and fracture behavior of the magnesium alloy macro-microstructure in the friction processing area were described. The aging and precipitation behavior of the friction-friction material and its effect on the mechanical properties are analyzed. The internal mechanism of the high-strength and high-toughness magnesium alloy is also realized. The microstructure of the as-cast Mg-Zn-Y-Zr alloy and the effect of mechanical coupling on the microstructure and the performance of the as-cast coarse-grained magnesium alloy were studied by changing the traveling speed. After the stirring and friction processing, the fiber area and the middle-lower part of the fibrous crystal grains are divided into fine crystal areas with fine equiaxed grains in the upper part, and the area of the fine crystal area is gradually reduced along with the increase of the traveling speed, but the reduction rate is reduced rapidly. After friction processing, the microstructure of the magnesium alloy was refined, and the as-cast crude crystal was recrystallized, the grain was refined to the micron level, and the coarse intercrystalline eutectic phase in the as-cast structure was broken into fine particles and dispersed. The element diffusion rate of the material is greatly improved under intense heat engine coupling, and the crushed I-phase (Mg3Zn6Y) particles are rapidly converted into W-phase (Mg3Zn3Y2) particles, and the core is a residual I-phase, and the edge is a W-phase core shell structure. The intense plastic deformation during the stirring and friction processing causes the fine crystal region to form an annular base surface texture which is parallel to the surface of the stirring needle. The fine crystal, the dispersion particle and the annular base surface texture are both favorable for the material strength and the plasticity of the material. As the advancing speed is improved, the grain size in the fine crystal region is reduced, the content of the dispersion particles is improved, the overall mechanical property is improved, the yield strength, the tensile strength and the elongation at the process parameters of 800 to 200 mm/ min reach 171 MPa,300 MPa and 27%, respectively, and compared with the as-cast base material, 53 per cent and 145 per cent. The heat engine-affected zone of the as-cast and in-state alloy stirring and friction processing is carried out for tissue analysis, and the microstructure evolution behavior of the micro-structure in the stirring and friction processing process is characterized by the characteristics of the micro-area microstructure of different parts, and the heat engine coupling effect is enhanced in the stirring friction processing process, In the coarse-grained magnesium alloy, the twin dynamic recrystallization occurs, and the grains promote the nucleation and the continuous and discontinuous dynamic recrystallization so as to refine the crystal grains. because the second phase content in the solid-state alloy is less, and a large amount of solution atoms cause the solute drag effect to obviously lower the dynamic recrystallization degree, the average grain size of the solid-state alloy stirring and friction processing fine crystal region material is large, And the strength is lower than the as-cast stirring friction processing fine crystal region material under the same parameters. For as-cast and high-temperature alloy stirring and friction processing of the fine crystal zone material under the process parameters of 800 rpm to 200 mm/ min, the aging conditions for 8h and 10h are respectively treated at 250 & deg; C for 8 h and 10 h. As the W-phase dispersion particles with good thermal stability and the barrier function of the W-phase nano-particles are precipitated along the grain boundary, the grain growth is slow, and the micron-level fine crystal tissue is still maintained under the state of the peak aging. And the 1 'rod-like precipitated phase is precipitated in the crystal grains under the peak aging, so that the strength of the material is further improved and the plasticity is maintained. The yield strength, tensile strength and elongation of the high-strength and high-toughness magnesium alloy are respectively improved by the yield strength, the tensile strength and the elongation of the high-strength and high-toughness magnesium alloy.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TG306;TG146.22
本文編號(hào)：2479809
[Abstract]:Compared with the traditional magnesium alloy, the rare earth magnesium alloy has the characteristics of high strength, high temperature resistance and corrosion resistance and the like, and has a wide application prospect in the field of light weight. At present, the preparation of rare-earth magnesium alloy is dominated by casting, and the strength and plasticity of the rare-earth magnesium alloy are one of the most important topics to be used to promote the use of the magnesium alloy. The stirring and friction processing is used as a large plastic deformation technology, and has the advantages of simple and convenient operation, high efficiency, environmental protection and the like, and can realize the local or integral modification of the material and improve the service performance of the material. In this paper, a high-performance Mg-Zn-Y-Zr alloy was prepared by friction stir processing, and the effects of the friction processing parameters and the initial state of the material on the microstructure, mechanical properties and fracture behavior of the magnesium alloy macro-microstructure in the friction processing area were described. The aging and precipitation behavior of the friction-friction material and its effect on the mechanical properties are analyzed. The internal mechanism of the high-strength and high-toughness magnesium alloy is also realized. The microstructure of the as-cast Mg-Zn-Y-Zr alloy and the effect of mechanical coupling on the microstructure and the performance of the as-cast coarse-grained magnesium alloy were studied by changing the traveling speed. After the stirring and friction processing, the fiber area and the middle-lower part of the fibrous crystal grains are divided into fine crystal areas with fine equiaxed grains in the upper part, and the area of the fine crystal area is gradually reduced along with the increase of the traveling speed, but the reduction rate is reduced rapidly. After friction processing, the microstructure of the magnesium alloy was refined, and the as-cast crude crystal was recrystallized, the grain was refined to the micron level, and the coarse intercrystalline eutectic phase in the as-cast structure was broken into fine particles and dispersed. The element diffusion rate of the material is greatly improved under intense heat engine coupling, and the crushed I-phase (Mg3Zn6Y) particles are rapidly converted into W-phase (Mg3Zn3Y2) particles, and the core is a residual I-phase, and the edge is a W-phase core shell structure. The intense plastic deformation during the stirring and friction processing causes the fine crystal region to form an annular base surface texture which is parallel to the surface of the stirring needle. The fine crystal, the dispersion particle and the annular base surface texture are both favorable for the material strength and the plasticity of the material. As the advancing speed is improved, the grain size in the fine crystal region is reduced, the content of the dispersion particles is improved, the overall mechanical property is improved, the yield strength, the tensile strength and the elongation at the process parameters of 800 to 200 mm/ min reach 171 MPa,300 MPa and 27%, respectively, and compared with the as-cast base material, 53 per cent and 145 per cent. The heat engine-affected zone of the as-cast and in-state alloy stirring and friction processing is carried out for tissue analysis, and the microstructure evolution behavior of the micro-structure in the stirring and friction processing process is characterized by the characteristics of the micro-area microstructure of different parts, and the heat engine coupling effect is enhanced in the stirring friction processing process, In the coarse-grained magnesium alloy, the twin dynamic recrystallization occurs, and the grains promote the nucleation and the continuous and discontinuous dynamic recrystallization so as to refine the crystal grains. because the second phase content in the solid-state alloy is less, and a large amount of solution atoms cause the solute drag effect to obviously lower the dynamic recrystallization degree, the average grain size of the solid-state alloy stirring and friction processing fine crystal region material is large, And the strength is lower than the as-cast stirring friction processing fine crystal region material under the same parameters. For as-cast and high-temperature alloy stirring and friction processing of the fine crystal zone material under the process parameters of 800 rpm to 200 mm/ min, the aging conditions for 8h and 10h are respectively treated at 250 & deg; C for 8 h and 10 h. As the W-phase dispersion particles with good thermal stability and the barrier function of the W-phase nano-particles are precipitated along the grain boundary, the grain growth is slow, and the micron-level fine crystal tissue is still maintained under the state of the peak aging. And the 1 'rod-like precipitated phase is precipitated in the crystal grains under the peak aging, so that the strength of the material is further improved and the plasticity is maintained. The yield strength, tensile strength and elongation of the high-strength and high-toughness magnesium alloy are respectively improved by the yield strength, the tensile strength and the elongation of the high-strength and high-toughness magnesium alloy.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TG306;TG146.22
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