AZ80鎂合金低壓脈沖磁場(chǎng)半連續(xù)鑄造過(guò)程的數(shù)值模擬和實(shí)驗(yàn)研究

AZ80鎂合金低壓脈沖磁場(chǎng)半連續(xù)鑄造過(guò)程的數(shù)值模擬和實(shí)驗(yàn)研究Numerical simulation and experimental research of low voltage pulsed magnetic field DC casting of AZ80 magnesium alloy

采用有限元方法對(duì)AZ80鎂合金低壓脈沖磁場(chǎng)半連續(xù)鑄造過(guò)程的電磁場(chǎng)、流場(chǎng)和溫度場(chǎng)進(jìn)行數(shù)值模擬，對(duì)鑄錠的組織進(jìn)行觀察和分析，并與普通半連續(xù)鑄造鑄錠晶粒組織進(jìn)行對(duì)比。模擬結(jié)果表明：在低壓脈沖磁場(chǎng)半連續(xù)鑄造過(guò)程中，結(jié)晶器中的熔體受脈沖電磁力作用產(chǎn)生強(qiáng)迫對(duì)流和電磁振蕩，使得熔體的徑向溫度梯度有所降低。組織觀察結(jié)果顯示，與普通半連續(xù)鑄錠相比，低壓脈沖磁場(chǎng)半連續(xù)鑄錠晶粒明顯細(xì)化，枝晶尖端發(fā)生鈍化。在低壓脈沖磁場(chǎng)半連續(xù)鑄造凝固過(guò)程中，結(jié)晶器壁附近形核的臨界形核半徑和臨界形核功有所降低，同時(shí)脈沖磁場(chǎng)形成的熔體對(duì)流使結(jié)晶器壁處形成的晶核隨著對(duì)流擴(kuò)散到熔池內(nèi)部，使形核率增加，另外脈沖磁場(chǎng)能夠通過(guò)尖端鈍化的方式抑制晶粒的生長(zhǎng)，從而造成低壓脈沖磁場(chǎng)鑄錠的晶粒細(xì)化。

The electromagnetic field, flow field and temperature field during the low voltage pulsed magnetic field direct chill casting of AZ80 magnesium alloy were simulated with finite element method, and the microstructure of the billet was observed by comparing those of billet by conventional direct chill (DC) casting process. The simulation results indicate that, during the low voltage pulsed magnetic field DC casting process, affected by electromagnetic force, forced convection and velocity vibration generate in the melt, leading to the reduced temperature grade of melt along the radial direction. The results show that the grains of the billet cast with low voltage pulsed magnetic are significantly refined and the tip of dendrite is rounded, compared with those of the conventional one. During the low voltage pulsed magnetic field DC casting process, the critical nucleation radius and critical nucleation energy near the crystallizer decrease, at the same time, the nuclei formed ahead the inner wall of crystallizer can be dispersed into the centre of the molten pool with the convection that caused by the pulsed magnetic field, which causes the increased nucleation rate. In addition, the growth of dendrite tip is inhibited by the passivation effect of the pulsed magnetic field, which leads to the grain refinement in the low voltage pulsed magnetic field direct chill casting billet.

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