本文選題：自孕育法　切入點：半固態(tài)　出處：《蘭州理工大學(xué)》2010年碩士論文

【摘要】： 孕育處理作為有效細(xì)化晶粒的方法被廣泛使用,同時合金組織細(xì)化處理是獲得優(yōu)質(zhì)半固態(tài)組織的主要方法之一。要獲得優(yōu)質(zhì)半固態(tài)組織的條件之一就是必須在合金熔體中產(chǎn)生足夠多的初始晶核,初始晶核在后期會演化出細(xì)小的半固態(tài)固相顆粒,因此希望初始晶核盡量細(xì)小和充足。 本文自主開發(fā)了一種能夠高效率制備優(yōu)質(zhì)半固態(tài)漿料的工藝,即自孕育鑄造法(Self-inoculation Method,簡稱SIM)。從晶粒來源和晶粒生長兩個角度入手,深入研究了樹枝晶破碎球化技術(shù)、控制形核抑制樹枝晶生長技術(shù),探討了SIM條件下初生固相的形態(tài)演變過程和球晶組織形成機(jī)理；系統(tǒng)研究了工藝參數(shù)(處理溫度、孕育劑加入量和導(dǎo)流器傾角)對AZ91D鎂合金半固態(tài)組織的影響規(guī)律；對不同成形工藝制備的AZ91D鎂合金鑄坯部分重熔組織進(jìn)行了初步研究,并在此基礎(chǔ)上對AZ91D鎂合金流變壓鑄和觸變壓鑄進(jìn)行了試驗研究。實驗結(jié)果表明： 1.自孕育劑在自孕育法中作用至關(guān)重要,在自孕育劑選擇上,應(yīng)盡量選取組織細(xì)小均勻,具有非枝晶組織的孕育劑；在孕育劑加入量上應(yīng)選取5-8%(質(zhì)量分?jǐn)?shù))。 2.在SIM工藝中,只要處理溫度(650-680℃)、孕育劑加入量(5-8%,質(zhì)量分?jǐn)?shù))和導(dǎo)流器傾角能夠良好地匹配,使出口溫度接近合金液相線溫度,便可以獲得優(yōu)良的半固態(tài)漿料。當(dāng)導(dǎo)流器角度和孕育劑加入量均在有效范圍內(nèi)時,隨著處理溫度的降低,初生α-Mg經(jīng)歷了由粗大樹枝晶→細(xì)小塊狀晶或近球形晶的演變過程。 3.半固態(tài)漿料在導(dǎo)流器出口組織細(xì)小均勻,水淬后檢測其平均顆粒大小為36μm。在壓射充型速度在2 m/s,經(jīng)5-10min保溫,溫度為585℃的AZ91D鎂合金半固態(tài)漿料能順利進(jìn)行流變壓鑄,在此工藝范圍內(nèi),晶粒平均尺寸為60-70μm且固相顆粒中無液相夾裹。壓鑄件的抗拉強(qiáng)度和硬度分別為185MPa和HV30=67.88。 4.采用自孕育法制備坯料觸變性良好,二次重熔后組織細(xì)小圓整,且從中心區(qū)域到邊緣區(qū)域晶粒大小均勻；大尺寸(Φ75mm)坯料在585℃保溫110min后采用與流變壓鑄工藝相同的參數(shù)進(jìn)行觸變壓鑄,初生相平均晶粒尺寸為80-90μm,固相率為58%。此時壓鑄件的抗拉強(qiáng)度和硬度分別為192MPa和HV30=68.74。
[Abstract]:Inoculation treatment is widely used as an effective method for grain refinement. At the same time, the refinement of alloy microstructure is one of the main methods to obtain high quality semi-solid microstructure. One of the conditions for obtaining high quality semi-solid microstructure is to produce enough initial nuclei in the alloy melt. The initial nucleus will evolve into fine semisolid solid particles at the later stage, so it is hoped that the initial nucleus will be as small and sufficient as possible. In this paper, we have developed a process of producing high quality semisolid slurry with high efficiency, that is, self-inoculation method by self-inoculation method. The spheroidization technology of dendritic fragmentation has been studied from the point of view of grain origin and grain growth. The technology of controlling nucleation to inhibit dendritic growth, the morphological evolution process of primary solid phase and the formation mechanism of spherulite structure under SIM were discussed, and the process parameters (treatment temperature, temperature, temperature) were studied systematically. The effect of inoculant addition and diversion angle on the semi-solid microstructure of AZ91D magnesium alloy was studied, and the partial remelting structure of AZ91D magnesium alloy billet prepared by different forming processes was studied. On this basis, rheological die-casting and thixotropic die-casting of AZ91D magnesium alloy were studied. 1. The self-inoculant plays an important role in the self-inoculation method. In the selection of self-inoculant, the inoculant with fine and uniform microstructure with non-dendritic structure should be selected as far as possible, and 5-8% (mass fraction) should be selected in the amount of inoculant. 2. In SIM process, as long as the treatment temperature is 650-680 鈩，

本文編號：1655741