本文關(guān)鍵詞：電磁場作用下稀土元素擴散效應(yīng)對半固態(tài)A356鋁合金凝固組織的影響　出處：《江西理工大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 半固態(tài)A356 電磁攪拌 稀土加入量 初生α相 稀土分布

【摘要】：半固態(tài)成形工藝(Semi-Solid Metal Forming),簡稱SSM,是指金屬在凝固過程中,在金屬固-液兩相區(qū)內(nèi),通過各種制漿方法,將金屬在凝固過程中形成的樹枝狀晶打碎,然后直接鑄造或先半固態(tài)鑄造,后重熔觸變,獲得具有一定球狀的顆粒狀組織,這種方法稱為半固態(tài)成形方法。通過這種方式獲得的鑄錠與傳統(tǒng)鑄造相比有諸多優(yōu)勢,比如能使鑄件內(nèi)部組織致密,氣孔少,偏析少,可形成復(fù)雜件,零件的力學(xué)性能提高等。本研究是以A356鋁合金為基體原料,通過施加電磁攪拌和添加微量稀土元素,探究在電磁場作用下稀土添加量對半固態(tài)A356鋁合金初生α相的影響,以及電磁攪拌及頻率對初生α相的影響機理和對稀土Ce在晶內(nèi)和晶界和不同徑向上的分布規(guī)律的影響。本文選擇Ce和Yb兩種稀土元素來探討在電磁攪拌作用下稀土的最佳加入量,其加入量分別為0.2%、0.4%、0.6%和0.8%Ce以及0.3%、0.5%、0.7%和0.9%Yb,分析了細(xì)化劑的細(xì)化機理是能否與基體晶粒形成共格關(guān)系,以及定量分析了最佳的稀土添加量的原因是與固-液界面前沿的成分過冷度有關(guān),得出了在低過熱度澆注,攪拌頻率30Hz,15s的情況下,最佳的稀土Ce和Yb的添加量為0.4%和0.7%Yb。在最佳的稀土Ce添加量的情況下,選擇10Hz、20Hz、30Hz和40Hz四個攪拌頻率來探究其對半固態(tài)A356鋁合金初生α相和稀土元素在晶內(nèi)和晶界上的分布的影響,得出了在低過熱度澆注下,在攪拌頻率為30Hz時初生α相最圓整和細(xì)小,其平均形狀因子和等級圓直徑分別為0.8和76.1μm,分析了頻率對組織和稀土Ce分布的影響,頻率過高或過低,都不利于熔體的擾動和溶質(zhì)原子的擴散,降低攪拌效果,使溶質(zhì)原子產(chǎn)生微觀偏聚。在利用30Hz的攪拌頻率,添加1.0%、1.4%、1.8%和2.2%Ce的情況下,對比了有無電磁攪拌,探究稀土元素及其化合物在鑄錠徑向上的存在形態(tài)和分布規(guī)律,得出了添加較多的稀土元素,稀土在A356鋁合金中呈針狀,且比較雜亂無序,有電磁攪拌時稀土分布稍加均勻,且在鑄錠上的分布從中心到外圍逐漸增大,在鑄錠半徑60%處達(dá)到最大值,之后又開始下降,而無電磁攪拌時,稀土分布無規(guī)律性,有較明顯的偏聚產(chǎn)生。
[Abstract]:Semi-Solid Metal forming process (SSM) means that the metal is in the solid-liquid two-phase region during the solidification process. Through various pulping methods, the dendritic grains formed in the solidification process of the metal were smashed, then cast directly or cast semi-solid first, then remelted and thixoed, and the granular structure with certain spherical shape was obtained. This method is called semisolid forming. Compared with traditional casting, the ingot obtained by this method has many advantages, such as compact internal structure, less porosity, less segregation, and can form complex parts. In this study, A356 aluminum alloy was used as the base material, by applying electromagnetic stirring and adding trace rare earth elements. The effect of rare earth addition on the primary 偽 phase of semisolid A356 aluminum alloy under the action of electromagnetic field was investigated. The influence mechanism of electromagnetic stirring and frequency on the primary 偽 phase and the distribution of rare earth ce in crystal, grain boundary and different radial direction are also discussed. In this paper, two rare earth elements ce and Yb are selected to study electromagnetic stirring. Use the optimum amount of rare earth. The amount of addition was 0.20.40% and 0.8% and 0.3B, respectively, and the amount of 0.30% and 0.9Yb was 0.7% and 0.9Yb, respectively. The refining mechanism of the refiner is analyzed whether it is coherent with the matrix grain, and the reason of the optimum addition of rare earth is related to the component undercooling at the front of the solid-liquid interface. The results show that under the condition of low superheat pouring and stirring frequency 30Hz / 15s. The optimum amount of rare earth ce and Yb was 0.4% and 0.7Yb.The optimum amount of rare earth ce was 10Hz. The effects of four stirring frequencies of 30Hz and 40Hz on the distribution of primary 偽 phase and rare earth elements in semisolid A356 aluminum alloy were investigated. When stirring frequency is 30 Hz, the primary 偽 phase is the most round and fine, its average shape factor and grade circle diameter are 0.8 and 76.1 渭 m, respectively. The influence of frequency on the distribution of rare earth ce and microstructure is analyzed. If the frequency is too high or too low, it will be unfavorable to the disturbance of melt and diffusion of solute atoms, reduce the agitation effect and make the solute atoms to produce micro-segregation. At the stirring frequency of 30 Hz, 1.0% 1.0% of solute atoms are added. In the case of 1.8% and 2.2, the existence and distribution of rare earth elements and their compounds in the radial direction of ingot were studied by comparing the presence and absence of electromagnetic stirring, and the addition of more rare earth elements was obtained. Rare earth in A356 aluminum alloy is needle-like and disorderly. The distribution of rare earth is a little more uniform when electromagnetic stirring occurs, and the distribution on the ingot increases gradually from the center to the periphery. When the radius of the ingot reaches the maximum at 60%, then it begins to decrease, but without electromagnetic stirring, the distribution of rare earth is irregular and the segregation of rare earth is obvious.
【學(xué)位授予單位】：江西理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG292

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