超声振动—真空差压协同场下ZL114A合金共晶硅生长特性研究

发布时间：2018-07-13 09:10

【摘要】：Al-Si合金由于具有良好的机械性能、比强度和耐蚀性,应用非常广泛,但是Al-Si合金在凝固条件下易形成粗大的树枝晶及片状的共晶硅组织,从而对铝合金铸件组织和性能产生影响。真空差压铸造是一种先进反重力精密成形技术,可以获得组织与性能优良的铝合金铸件。超声处理技术是一种高效、无污染的物理细化晶粒的方法。将超声处理技术与真空差压铸造技术结合,探讨超声振动-真空差压协同场下铝硅合金共晶硅生长特性,可以为真空差压铸造高质量复杂薄壁铝合金铸件提供理论指导及技术支持。以ZL114A合金为研究对象,通过分析超声功率与凝固压力等工艺参数下真空差压铸造铝合金显微硬度、共晶硅生长取向及形貌,探索超声振动-真空差压协同场对ZL114A合金共晶硅生长特性的影响规律和机理。结果表明,超声功率及凝固压力均对铝合金显微硬度、共晶硅生长取向和形貌影响显著。当凝固压力一定时,ZL114A合金显微硬度随着超声功率的增加,呈现先增加后减少的趋势,超声功率600W时达到最好;共晶硅在600W时的择优生长面(111)和(220)被强烈抑制,而(311)面择优取向消失,共晶硅趋向于各向同性生长,使共晶硅形貌细小,圆整化。在同一超声功率下,随着凝固压力的增加,ZL114A合金显微硬度逐渐增加,共晶硅向择优面(111)、(220)及(331)的生长越困难,共晶硅越细小弥散。获得最佳的超声振动-真空差压协同参数为超声功率600W和凝固压力350KPa,建立了超声振动-真空差压协同场下超声功率、凝固压力和显微硬度之间的数学关系模型,同时建立了超声振动-真空差压协同场下共晶硅组织演化模型,并推导了超声振动-真空差压协同作用下空化挤渗数学模型:合金在凝固阶段枝晶间X处的空化挤渗量ΔG越大,对枝晶及共晶硅的作用越强,则铝合金微观组织越均匀细小。该研究结果为Al-Si系合金在真空差压铸造中的应用提供了新的途径,为复合场在真空差压铸造铝合金工艺技术的应用和推广奠定了理论和技术基础。
[Abstract]:Al-Si alloy is widely used because of its good mechanical properties, specific strength and corrosion resistance. However, it is easy to form coarse dendrite and eutectic silicon structure under solidification condition. Thus, the microstructure and properties of aluminum alloy castings are affected. Vacuum differential pressure casting (VDPC) is an advanced anti-gravity precision forming technology, which can obtain aluminum alloy castings with good microstructure and properties. Ultrasonic treatment is an efficient and pollution-free physical grain refinement method. By combining ultrasonic treatment with vacuum differential pressure casting, the growth characteristics of Al-Si alloy eutectic silicon under the synergistic field of ultrasonic vibration and vacuum differential pressure were investigated. It can provide theoretical guidance and technical support for high quality and complex thin wall aluminum alloy castings in vacuum differential pressure casting. Taking ZL114A alloy as the research object, the microhardness, eutectic silicon growth orientation and morphology of vacuum differential pressure casting aluminum alloy under ultrasonic power and solidification pressure were analyzed. The effect of ultrasonic vibration and vacuum differential pressure synergy field on the growth characteristics of ZL114A alloy eutectic silicon was investigated. The results show that the influence of ultrasonic power and solidification pressure on microhardness, growth orientation and morphology of eutectic silicon is significant. When the solidification pressure is constant, the microhardness of ZL114A alloy increases first and then decreases with the increase of ultrasonic power, and the optimum growth surface (111) and (220) of eutectic silicon at 600W are strongly inhibited. However, the preferred orientation of (311) plane disappears and eutectic silicon tends to grow isotropic, which makes the morphology of eutectic silicon fine and rounded. Under the same ultrasonic power, the microhardness of ZL114A alloy increases gradually with the increase of solidification pressure. The more difficult the eutectic silicon grows to the preferred plane (111), (220) and (331), the smaller the dispersion of eutectic silicon is. The optimum synergetic parameters of ultrasonic vibration and vacuum differential pressure are obtained as follows: ultrasonic power 600W and solidification pressure 350 KPA. The mathematical model of ultrasonic power, solidification pressure and microhardness under ultrasonic vibration vacuum differential pressure synergy field is established. At the same time, the microstructure evolution model of eutectic silicon under the synergistic field of ultrasonic vibration and vacuum differential pressure is established, and the mathematical model of cavitation extrusion under the synergistic action of ultrasonic vibration and vacuum differential pressure is deduced. The stronger the effect on dendrite and eutectic silicon, the smaller the microstructure of aluminum alloy. The results provide a new way for the application of Al-Si alloy in vacuum differential pressure casting and lay a theoretical and technical foundation for the application and popularization of composite field in vacuum differential pressure casting aluminum alloy technology.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21

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