圆台形冒口脉冲磁致振荡处理对Al-Si合金铸锭凝固均质化的影响

Effect of Pulsed Magneto-oscillation Treatment of Round-table Hot-top on Solidification Homogenization of Al-Si Alloy Ingot

脉冲磁致振荡凝固均质化是一项新技术。研究了圆台形冒口脉冲磁致振荡处理对Al-Si合金铸锭流场、凝固组织和宏观偏析的影响。结果表明:对圆台形冒口施加脉冲磁致振荡的铸锭内形成了两个方向相反的环流,即下环流和上环流,下环流方向为中心向下、边缘向上,上环流方向则与之相反。环流的形成有利于铸锭内温度场的均匀化和自由晶在铸锭中心沉降。浇注试验结果显示:圆台形冒口经受脉冲磁致振荡处理的铸锭冒口部位在液相线附近温度下降快速,锭身中轴线处溶质分布更为均匀,偏析指数极差从0.36降低至0.19,成分标准偏差从0.26降低至0.10。大功率(峰值电流为450 KIA)脉冲磁致振荡处理有利于细化Al-3%Si(质量分数)合金铸锭的凝固组织,而小功率(峰值电流为150 KIA)脉冲磁致振荡处理有利于改善溶质分布的均匀性。因铸锭上部正偏析区缩小,且冒口尺寸较小,脉冲磁致振荡处理有利于提高铸锭的收得率。

Solidification homogenization by pulsed magneto-oscillation is a novel technology.The effect of pulsed magneto-oscillation treatment of round-table hot-top on the flow field,solidification structure and macrosegregation in Al-Si alloy ingot was investigated.The results showed that the ingot whose round-table hot-top was subjected to pulsed magneto-oscillation treatment formed two opposite circulations,i.e.,lower and upper circulations,and the direction of the former was downward from the center and upward at the edge,whereas the direction of the latter was opposite to that of the former.The formation of circulations was favorable for homogenization of temperature field in the ingot and for settlement of the free crystal in the ingot center.From the results of pouring test it was seen that the ingot whose round-table hot-top was subjected to pulsed magneto-oscillation treatment showed rapid decrease in temperature near the liquidus line at the riser,the distribution of solute was more uniform at the central axis of the ingot body,the segregation index range was reduced from 0.36 to 0.19,and the standard deviation of composition was reduced from 0.26 to 0.10.Moreover,the high-power(peak current of 450 KIA)pulsed magnetic oscillation treatment was beneficial to refinement of structure of Al-3%Si(mass percent)alloy ingot,whereas the low-power(peak current of 150 KIA)treatment was beneficial to improvement in uniformity of the solute distribution.The pulsed magneto-oscillation treatment helped to increase yield of the ingot due to both the reduction of positive segregation area in the upper part of the ingot and the relatively small hot-top.