交变磁场调控下铝合金熔体真空差压分级加压凝固行为研究

The solidification stage of conventional vacuum counter-pressure casting adopts constant pressure difference, for complicated aluminum alloy castings of asymmetrical thickness, the feeding channel is gradually reduced at later stage of solidification, and the interdendritic flow of molten aluminum alloy is hindered, which lead to difficult solidification feeding. In the present study, the ZL114A is used as raw material, and alternating magnetic field is impose during grade-pressuring solidification of vacuum counter-pressure casting. Based on the different casting conditions, such as the intensity of alternating magnetic field, primary solidification pressure, grade-pressuring pressure difference and time,the morphology, growth orientation, dendrite arm spacing and density under vacuum counter-pressure casting aluminum alloy are studied systematically. During the grade-pressuring solidification of vacuum counter-pressure casting under alternating magnetic field regulation, the characteristic and rule of aluminum alloy dendrite growth are explored, and the optimal coupled relationship of convection effect of alternating magnetic field and extrusion and infiltration effect during vacuum counter-pressure grade-pressuring solidification is obtained. The model of dendrite growth dynamics and convection-extrusion and infiltration are established during the grade-pressuring solidification of vacuum counter-pressure casting under alternating magnetic field regulation for disclosing the solidification behavior of molten aluminum alloy, which can provide the scientific guidance and theory for vacuum counter-pressure casting complicated aluminum alloy precision castings, and have the enormous application value and broad prospects in many fields such as aviation, spaceflight and automobile industry, etc.

传统的真空差压铸造凝固阶段均采用固定不变的压差，对于壁厚不均匀的复杂铝合金铸件，凝固后期补缩通道逐渐缩小，铝合金熔体在枝晶间流动受阻，凝固补缩困难。项目以ZL114A铝合金为研究对象，在真空差压分级加压凝固过程中施加交变磁场，基于对不同交变磁场强度、一级凝固压力、分级加压压差、分级加压时间等条件下真空差压铸造铝合金枝晶生长形貌、取向、间距大小和致密度的系统研究，探讨交变磁场调控下真空差压分级加压凝固铝合金枝晶生长特性及其规律，获得铝合金熔体的交变磁场对流效应与真空差压分级加压挤渗效应的最佳融合关系，建立交变磁场调控下真空差压分级加压凝固铝合金枝晶生长动力学与对流挤渗模型，揭示交变磁场调控下铝合金熔体真空差压分级加压凝固行为，为真空差压铸造复杂铝合金精密铸件提供科学依据与理论支撑，在航空航天、汽车工业和其它科学领域具有巨大的应用价值和广阔前景。

传统的真空差压铸造凝固阶段均采用固定不变的压差，对于壁厚不均匀的复杂铝合金铸件，凝固后期补缩通道逐渐缩小，铝合金熔体在枝晶间流动受阻，凝固补缩困难。项目以ZL114A铝合金为研究对象，在真空差压分级加压凝固过程中施加交变磁场，研究不同交变磁场强度、分级加压压差、分级加压时间等条件下真空差压铸造铝合金枝晶生长形貌、取向、间距大小和致密度的变化规律。结果表明，磁场强度24mT、加压压差160kPa、加压时间225s时铸件致密度最佳。探讨了交变磁场调控下真空差压分级加压凝固铝合金枝晶生长特性及其规律。经过交变电磁场处理后，真空差压铸造ZL114A合金试样的二次枝晶间距普遍降低，当交变电磁场为24mT时，铝合金试样的二次枝晶间距达到最小，二次枝晶臂球化或椭球化趋势明显。随着分级加压压差的增大，铸件二次枝晶臂间距逐步减小，枝晶组织被显著细化。α-Al枝晶的（111）晶面方向成为施加交变电磁场后的主要生长取向，同时在（200）以及（220）晶面方向出现一定择优生长；随着分级加压压差的增强，α-Al在（311）晶面方向上的衍射强度逐步地减弱。获得了铝合金熔体的交变磁场对流效应与真空差压分级加压挤渗效应的最佳融合关系，建立了交变磁场调控下真空差压分级加压凝固铝合金枝晶生长动力学与对流挤渗模型，揭示了交变磁场调控下铝合金熔体真空差压分级加压凝固行为。本项目的研究成果为真空差压铸造复杂铝合金精密铸件提供科学依据与理论支撑，在航空航天、汽车工业和其它科学领域具有巨大的应用价值和广阔前景。