發(fā)布時間：2018-03-06 02:15

  本文選題：AZ91鎂合金　切入點：電磁攪拌　出處：《沈陽工業(yè)大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：鎂合金的比強(qiáng)度高、材料可回收率高、電磁屏蔽性好,因此越來越受到現(xiàn)代工業(yè)的重視,但鎂合金在室溫下較差的塑性,使得其應(yīng)用的廣泛性不及其它金屬材料。電磁攪拌可以細(xì)化晶粒,增加等軸晶,減少樹枝晶,同時因電磁力而產(chǎn)生熔體的對流使其溫度場均勻化,能減輕偏析。此外,鎂合金也可通過固溶處理和時效處理提升力學(xué)性能。本文以AZ91為研究對象,采用不同電磁攪拌工藝參數(shù)和熱處理方法,改善AZ91鎂合金的顯微組織,提高合金的力學(xué)性能;并通過第一性原理,對β相和Mg基固溶體進(jìn)行熱穩(wěn)定性、電子性質(zhì)和彈性性質(zhì)的計算。結(jié)果表明:AZ91鎂合金的力學(xué)性能和顯微組織均隨電磁攪拌頻率的增加而得到改善,在電磁頻率為10Hz、電流為150A時力學(xué)性能最好,合金的抗拉強(qiáng)度、伸長率和硬度分別為163MPa、5.3%和58.6HB;此時晶粒的細(xì)化最明顯,平均晶粒尺寸為93μm,α-Mg相由樹枝狀轉(zhuǎn)變?yōu)樗N薇狀,Al元素固溶度提升,同時基體中出現(xiàn)了孿晶;原先粗大的β相得到細(xì)化和碎化。晶粒的細(xì)化,β相的碎化,Al、Zn的固溶強(qiáng)化以及孿晶,使得合金的力學(xué)性能得到提升。通過對電磁攪拌AZ91鎂合金進(jìn)行固溶處理,合金力學(xué)性能隨著固溶時間的增加呈先增加后減少的趨勢,在36h時達(dá)到最大值,此時合金的抗拉強(qiáng)度、伸長率和硬度分別為229MPa、8.8%和67.8HB;此時β相已大量溶解,剩余的β相呈彌散分布。通過對固溶36h的合金進(jìn)行時效處理,合金的抗拉強(qiáng)度和硬度隨著時效時間的增加呈先降低后增加再降低的趨勢,在12h時達(dá)到最大值,此時合金的抗拉強(qiáng)度和硬度分別為247MPa和78.1HB,而伸長率一直降低;時效過程中晶粒呈長大趨勢,而β相以不連續(xù)析出為主,伴隨少量連續(xù)析出。第一性原理計算結(jié)果表明,β相可以自發(fā)形成并且穩(wěn)定存在,并且具有較高的楊氏模量,呈脆性,因此當(dāng)β相以細(xì)小狀態(tài)彌散分布時,會對基體產(chǎn)生強(qiáng)化作用;Mg24、Mg23Al1、Mg23Zn1和Mg_(22)Al_1Zn_1摻雜固溶體中,Mg_(22)Al_1Zn_1同時具有相對較低的形成熱和結(jié)合能,以及良好的塑性,說明Al、Zn元素的共同固溶利于Mg基固溶體的形成和穩(wěn)定存在,并且提升其力學(xué)性能。
[Abstract]:Magnesium alloys have high specific strength, high recovery rate and good electromagnetic shielding, so they are paid more and more attention by modern industry, but the plasticity of magnesium alloys is poor at room temperature. Electromagnetic stirring can refine grain, increase equiaxed crystal, reduce dendrite, at the same time, the convection of melt caused by electromagnetic force can homogenize its temperature field and reduce segregation. The mechanical properties of magnesium alloys can also be improved by solution treatment and aging treatment. In this paper, different electromagnetic stirring process parameters and heat treatment methods are used to improve the microstructure and mechanical properties of AZ91 magnesium alloys. The thermal stability, electronic properties and elastic properties of 尾 -phase and Mg-based solid solution were calculated by first-principle method. The results show that the mechanical properties and microstructure of the 尾 -phase and Mg-based solid solution are improved with the increase of electromagnetic stirring frequency. When the electromagnetic frequency is 10 Hz and the current is 150 A, the mechanical properties of the alloy are the best. The tensile strength, elongation and hardness of the alloy are 163MPA 5.3% and 58.6 HB.The grain refinement is the most obvious. The average grain size was 93 渭 m, 偽 -Mg phase changed from dendritic to rose-like Al element, and twins appeared in the matrix, the 尾 phase was refined and shredded. The mechanical properties of the alloy were improved by the solution treatment of electromagnetic stirring AZ91 magnesium alloy. With the increase of the solution time, the mechanical properties of the alloy increased first and then decreased, and reached the maximum value at 36 h, when the tensile strength of the alloy was increased, The elongation and hardness of the alloy were 229MPA (8.8%) and 67.8 HB.The 尾 phase was dissolved and the remaining 尾 phase was dispersed. The alloy was treated by aging treatment for 36 h. With the increase of aging time, the tensile strength and hardness of the alloy decreased first, then increased and then decreased, reaching the maximum value at 12 h. The tensile strength and hardness of the alloy were 247MPa and 78.1 HBs, respectively, and the elongation decreased continuously. In the aging process, the grain size tends to be long and the 尾 phase is mainly discontinuous precipitation, accompanied by a small amount of continuous precipitation. The first principle calculation results show that the 尾 phase can spontaneously form and exist stably, and has higher Young's modulus and brittleness. Therefore, when the 尾 phase is dispersed in fine state, it will strengthen the matrix. Mg _ (24) mg _ (23) Al _ (1) O _ (mg _ (23) Zn _ (1) Zn _ (1)) and Mg_(22)Al_1Zn_1 doped solid solution have relatively low formation heat, binding energy, and good plasticity at the same time. The results show that the common solution of Al ~ (2 +) Zn is beneficial to the formation and stability of Mg-based solid solution and improves its mechanical properties.
【學(xué)位授予單位】：沈陽工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG146.22;TG166.4

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本文編號：1572896