【摘要】：難混溶合金是一種具有廣泛工業(yè)應用前景的合金,但由于其獨特的凝固特性,在常規(guī)凝固條件下,極易形成嚴重的比重偏析,導致其優(yōu)異的性能無法充分發(fā)揮。近年來,隨著超導技術和Bitter磁體技術的發(fā)展,實現(xiàn)了10-30 T量級的恒定、長時的強磁場。研究表明,其極強的洛倫茲力、磁場力、磁場能量效應對金屬的凝固過程有著深遠的影響,如合金相取向、晶粒遷移、枝晶細化等,顯示其與常規(guī)凝固截然不同的規(guī)律和機制,將超強磁場應用于難混溶合金的凝固,以期望解決其比重偏析嚴重的問題,至今研究尚不深入。因此,開展磁場下難混溶合金凝固研究的意義非常重大。本文以Zn-Bi難混溶合金為研究對象,對0-30 T磁場下的難混溶合金的凝固行為開展了深入研究,并嘗試探索常規(guī)重力和常規(guī)冷卻條件下均質(zhì)難混溶合金的制備途徑。獲得如下研究成果:研究了0-30 T縱向強磁場對成分處于難混溶區(qū)內(nèi)的Zn-Bi合金凝固過程中第二相液滴偏析行為的影響規(guī)律。發(fā)現(xiàn)施加強靜磁場可以顯著抑制第二相Bi液滴的Stokes沉降運動和Marangoni運動,但高達29 T的強靜磁場仍無法完全消除Spinodal分解造成的成分偏析。強靜磁場對Zn-Bi合金中Bi液滴的形核與長大過程影響顯著:磁場大于17.4 T時,Bi液滴以純擴散方式長大;小于17.4T時,則以碰撞、凝并方式長大。研究了0-30 T縱向強磁場下冷卻速度對Zn-6wt.%Bi難混溶合金凝固組織形貌的影響規(guī)律。結果表明,淬火冷卻的Zn-6wt.%Bi難混溶合金的表層等軸晶中形成了一種鏈狀組織;隨爐冷卻則形成了一種Bi包圍Zn相的殼型凝固組織,并基于熱電磁流理論探討了殼型組織的形成機制。研究了橫/縱向磁場誘導的熱電磁力對合金凝固組織中第二相分布的影響規(guī)律。結果表明,1 T量級的橫/縱向磁場在熔體中產(chǎn)生了顯著的熱電磁力,并形成了宏觀的熱電磁流動,顯著改變了Bi液滴在空間的分布規(guī)律。針對采用29 T強靜磁場和淬火冷卻條件仍無法抑制具有強烈液液分離傾向的難混溶合金的Stokes沉降和Marangoni凝并導致的宏觀偏析問題,提出了強磁場復合交變電流調(diào)控難混溶合金凝固組織的新方法。結果表明,當磁感應強度為10 T、電磁體積力為5×105 N/m~3、交變電流頻率為50 Hz時,Zn-10wt.%Bi和Zn-20wt.%Bi合金凝固組織中Bi顆粒的粒徑最小且最彌散,獲得了幾乎均勻的凝固組織。過低或過高的交變電流頻率都會顯著促進Bi液滴的碰撞和凝并,加重合金的偏析。由于在研究強靜磁場對成分處于非難混溶區(qū)內(nèi)的合金凝固影響的過程中發(fā)現(xiàn),縱向強磁場對Zn-84~97.3wt.%Bi合金凝固組織的取向具有顯著的影響,對比研究了磁場下Zn-95wt.%Bi合金和具有偏晶特性的Bi-Mn合金組織中析出相的取向機制。發(fā)現(xiàn)Zn-95wt.%Bi合金在0 T和6 T條件下其凝固組織顯示出共同的磁各向同性,6 T條件下的凝固組織在平行于磁場方向上表現(xiàn)出最小的抗磁化強度特征;在2 T和4 T條件下則顯示出共同的磁各向異性。在30 T和60℃/min的冷卻條件下,Bi-Mn合金凝固組織中的α-BiMn的取向與磁場方向平行;在30 T和5℃/min的冷卻速度時,則是一種呈多層分布的組織。本文對磁場作用下不同成分的Zn-Bi難混溶合金凝固過程的系統(tǒng)研究,豐富了磁場下難混溶合金的凝固理論,對均質(zhì)的難混溶合金的制備具有重要的學術指導價值和工程意義。
[Abstract]:It is a kind of alloy with wide industrial application prospect, but due to its unique solidification characteristics, it is very easy to form serious specific gravity segregation under the condition of normal solidification, which leads to its excellent performance. In recent years, with the development of the superconducting technology and the Bitter magnet technology, a constant and long-term strong magnetic field of the order of 10-30T is realized. The research shows that the strong Lorentz force, the magnetic field force and the magnetic field energy effect have a far-reaching influence on the solidification process of the metal, such as the orientation of the alloy, the grain migration, the dendrite refinement and the like, and shows the rule and the mechanism which are completely different from the conventional solidification, The super-strong magnetic field is applied to the solidification of the immiscible alloy, so as to solve the problem that the specific gravity segregation is serious, and the research is not yet in-depth. Therefore, it is very important to carry out the research on the solidification of the immiscible alloy under the magnetic field. In this paper, the study of the solidification behavior of the immiscible alloy under the 0-30T magnetic field is carried out by taking the Zn-Bi difficult-to-heat transfer alloy as the research object, and the preparation method of the immiscible alloy under the conventional gravity and the conventional cooling condition is also tried. The effect of 0-30T longitudinal strong magnetic field on the segregation behavior of the second phase in the solidification process of Zn-Bi alloy is studied. It is found that the static magnetic field can significantly inhibit the Stokes settlement movement and the Marangoni motion of the second phase Bi droplets, but the strong static magnetic field up to 29T still cannot completely eliminate the component segregation caused by the Spinoidal decomposition. The effect of the strong static magnetic field on the nucleation and growth of Bi droplets in the Zn-Bi alloy is significant: when the magnetic field is greater than 17.4 T, the Bi droplets grow up in pure diffusion mode; when the magnetic field is less than 17.4 T, the Bi droplets grow up in a collision, coagulation and manner. The influence of the cooling rate of 0-30T in the longitudinal high magnetic field on the solidification structure of the hard-immiscible alloy with Zn-6wt.% Bi was studied. The results show that a chain-like structure is formed in the surface of the surface of the hard-cooled Zn-6 wt.% Bi-immiscible alloy, and a shell-type solidification structure surrounding the Zn phase is formed with the cooling of the furnace, and the formation mechanism of the shell-type tissue is discussed based on the theory of the heat-electromagnetic flow. The influence of the thermal electromagnetic force induced by the transverse/ longitudinal magnetic field on the second phase distribution in the solidification structure of the alloy is studied. The results show that the transverse/ longitudinal magnetic field on the order of 1 T has a significant thermal electromagnetic force in the melt, and a macroscopic thermal electromagnetic flow is formed, which significantly changes the distribution of Bi droplets in the space. A new method for controlling the solidification structure of the immiscible alloy with strong magnetic field compound alternating current is proposed for the problems of Stokes settlement and Marangoni's setting and the macro-segregation of the immiscible alloy with strong liquid-liquid separation tendency, which are still not restrained by the 29T strong static magnetic field and the quenching cooling condition. The results show that when the magnetic induction intensity is 10T, the electromagnetic volume is 5-105N/ m ~ 3, the frequency of the alternating current is 50 Hz, the particle size of Bi particles in the solidification structure of Zn-10 wt.% Bi and Zn-20wt.% Bi alloy is the smallest and the most diffuse, and the almost uniform solidification structure is obtained. The low or too high alternating current frequency can significantly promote the collision and coagulation of the Bi droplets and increase the segregation of the alloy. It is found that the orientation of the solidification structure of Zn-84-97.3 wt.% Bi alloy has a significant influence on the orientation of the solidification structure of Zn-84-97.3 wt.% Bi alloy during the study of the influence of the static magnetic field on the solidification of the alloy in the immiscible region. In this paper, the orientation mechanism of precipitation phase of Zn-95 wt.% Bi alloy and Bi-Mn alloy was studied. It is found that Zn-95 wt.% Bi alloy exhibits common magnetic isotropy under the condition of 0 T and 6 T, and the solidification structure under the condition of 6T shows the minimum anti-magnetization characteristic in the direction parallel to the magnetic field, and the common magnetic anisotropy is displayed under the condition of 2T and 4T. In the cooling condition of 30 T and 60 鈩，

本文編號：2503348