超声振动－真空差压协同场下铝合金熔体凝固行为研究

The interdendritic flow of molten aluminum alloy is hindered during the solidification process, because of the coarse dendrites in aluminum alloy castings. It is difficult to obtain the refined grains and dense microstructures of complex and thin-walled aluminum alloy precision castings. In the present study, the ZL114A is used as raw material. Based on the different casting conditions, such as the ultrasonic vibration frequency, applying vibration time, holding solidification pressure and time, the morphology, growth orientation, spacing and density of primary dendrites and secondary dendrites in vacuum counter-pressure casting thin-walled aluminum alloy are studied systematically. During the solidification of molten aluminum alloy, the characteristic and rule of dendrite growth are explored under ultrasonic vibration and vacuum counter-pressure coordination field, and the optimal coupled relationship of ultrasonic vibration cavitation and extrusion and infiltration effect during vacuum counter-pressure casting is obtained. The model of growth dynamics of dendrite and cavitation-extrusion and infiltration are established during solidification of aluminum alloy under ultrasonic vibration and vacuum counter-pressure coordination field for disclosing the solidification behavior of molten aluminum alloy. The achievements of the present study can provide the scientific guidance and theory for vacuum counter-pressure casting thin-walled aluminum alloy precision castings, and have the enormous application value and broad prospects in many fields, such as aviation, spaceflight and automobile industry, etc.

铝合金铸造组织枝晶粗大，在凝固过程中铝合金熔体在枝晶间流动受阻，凝固补缩困难，难以获得晶粒细小、组织致密的复杂薄壁铝合金精密铸件。项目以ZL114A铝合金为研究对象，基于对不同超声振动频率、施振时间、凝固保压压力、保压时间等条件下真空差压铸造铝合金薄壁铸件一次枝晶和二次枝晶生长形貌、取向、间距大小和致密度的系统研究，探讨超声振动－真空差压协同场下铝合金熔体的枝晶生长特性及其规律，获得铝合金熔体的超声振动空化效应与真空差压挤渗效应的最佳融合关系，建立超声振动－真空差压协同场下铝合金枝晶生长动力学与空化挤渗模型，揭示超声振动－真空差压协同场下铝合金熔体的凝固行为。项目的研究成果可以为真空差压铸造复杂薄壁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。

铝合金铸造组织枝晶粗大，在凝固过程中铝合金熔体在枝晶间流动受阻，凝固补缩困难，难以获得晶粒细小、组织致密的复杂薄壁铝合金精密铸件。项目以ZL114A铝合金为研究对象，在超声振动－真空差压协同场下，系统研究了不同超声功率、施振温度、凝固压力等工艺参数下真空差压铸造铝合金致密度及枝晶生长形貌、取向、间距大小。结果表明，最佳超声振动－真空差压协同工艺参数为超声功率600W、施振温度720℃、凝固压力350KPa以上。当超声功率600W，凝固压力350KPa时，超声振动－真空差压协同作用的ZL114A铝合金共晶硅的形貌发生了明显的改变，由粗大的板条状向细小的短棒状转变，共晶硅的择优生长取向（220）及（311）面基本消失，共晶硅的择优取向被完全抑制，而且二次枝晶间距最小。并建立了超声振动－真空差压协同场下铝合金枝晶生长动力学模型，得到铝合金熔体的超声振动空化效应与真空差压挤渗效应的最佳融合关系，建立了超声振动－真空差压协同场下铝合金空化挤渗模型，揭示了超声振动－真空差压协同场下铝合金熔体的凝固行为。项目的研究成果可以为真空差压铸造复杂薄壁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。