旋轉(zhuǎn)磁場作用下A356-La合金徑向凝固組織形貌及稀土元素分布

旋轉(zhuǎn)磁場作用下A356-La合金徑向凝固組織形貌及稀土元素分布Radial solidification microstructure and rare earth elements distribution of A356-La alloy under rotating magnetic field

利用OM、SEM分析低過熱度澆注、雙向低頻電磁攪拌和稀土元素細(xì)化處理復(fù)合技術(shù)制備的A356-La鋁合金鑄錠，考察電磁場作用時間恒定時，磁場頻率對合金鑄錠徑向顯微組織和稀土元素分布規(guī)律的影響，并在最佳工藝參數(shù)上探討熔體攪拌方式對徑向組織演化及均勻性的影響。結(jié)果表明：磁場頻率增加，晶粒球化程度顯著，生長方式由枝晶向球晶轉(zhuǎn)變，徑向組織以及稀土元素點(diǎn)狀彌散分布均勻性增強(qiáng)，磁場頻率25 Hz、0.7R時達(dá)到最佳，平均等積圓直徑和形狀因子分別為36.2 μm和0.82；合金徑向3個采集點(diǎn)晶粒直徑和形狀因子的平均值達(dá)到41.6 μm和0.76。雙向連續(xù)攪拌作用于熔體時，組織形貌和均勻性優(yōu)于單向連續(xù)攪拌、雙向間歇攪拌。此攪拌方式加快熔體內(nèi)部質(zhì)量傳輸、熱量傳遞進(jìn)程，一定程度上避免集膚效應(yīng)對組織均勻性的不利影響。

A356-La aluminum alloy ingot prepared by composite technology of low superheat pouring, two-way low-frequency electromagnetic stirring and rare earth element refinement were analyzed by OM and SEM, which contains the microstructure with fine size and round shape primary phase. The influence of magnetic field frequency on the radial microstructure and distribution of rare earth elements in alloy ingot was investigated, when the stirring time of electromagnetic field was constant. The results indicate that when the frequency of magnetic field increases, the degree of grain spheroidization becomes significantly better. The growth mode of grain changes from dendrite grain to globular grain, and the distribution of microstructure along the radial and rare earth element becomes uniform. When the magnetic field frequency is 25 Hz and the radius is 0.7R, the morphology of the primary phase can reach at optimum. The average equal-area circle diameter and shape factor of the primary phase are 36.2 μm and 0.82, respectively. The average primary phase diameter and shape factor from the three collecting points in the radial direction are 41.6 μm and 0.76, respectively. In addition, the influence of melt stirring ways on the evolution and uniformity of microstructure along the radial was discussed under the optimum technological parameters. It indicates that the morphology and uniformity of the microstructure obtained from the two way continuous stirring are better than the single way continuous stirring and two-way intermittent stirring. This stirring way accelerates the internal mass transfer and heat transfer process of the melt, and then, to a certain extent, the adverse effect of skin effect on uniformity of solidification structure can be avoided.

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