低压铸造过程弹性波传播对两相区补缩的作用机理

ZL205A Aluminum alloy is large crystallization range aluminum alloy, shrinkage tendency is very serious. The aerospace ZL205A castings produced by the low pressure die casting must pass the 100% X-ray inspection, and the requirements on the density of casting is very strict. This project introduces the vibration mechanism during the low pressure die casting process, and through the further investigation of the characteristics of vibration process. The scientific essence of the vibration issue is elastic-wave transmitting behavior in the viscoelastic medium.The physical and the mathematic models of the elastic-wave transmission in two-phase media and viscoelastic medium have been established based on the simulation of the solidification process. The numerical simulation technique research for the rule of the elastic waves that caused by Vibration transfers and decay in viscoelastic medium, study the loosening mechanism of elastic wave on the solid framework in porous structure, the feeding mechanism of elastic wave on the melt in porous structure and the influence of the vibration on the feeding process during the solidification under low pressure.The feature of transmission and the rules of the elastic waves in variable temperature viscoelastic medium have been obtained. The feeding mechanism of the vibration in low press casting of large crystallization range alloy castings has been proposed.This work could provide technical foundation to improve the feeding capacity of the large crystallization alloy casting, which is produced by low pressure die casting process. Furthermore, this work could also provide theoretical basis for the Vibration feeding mechanism of mushy solidification alloy under low pressure, which may further enrich and develop solidification control technology.

ZL205A铝合金是典型的宽结晶合金，缩松倾向十分严重。采用低压铸造技术生产的航空、航天ZL205A铸件100% X光探伤，对铸件的致密度有极其严格的要求。本项目在低压铸造中引入振动机制，并且通过研究振动过程的特征，凝练了振动问题的科学本质，既弹性波在粘弹性介质中传播问题。在铸件凝固数值模拟研究基础上，建立弹性波在弹性及粘弹性双相介质中传播的物理模型与数学模型，并采用数值模拟技术研究振动引起的弹性波在粘弹性介质中传播及衰退规律，研究弹性波对双相介质结构的固相骨架的松散机制与双相介质结构中合金流体的补缩流动机制，研究振动对低压铸造过程补缩的影响。获得弹性波在变温、粘弹性介质中传播的特征及规律；获得振动条件下宽结晶合金低压铸造铸件补缩机理，为提高宽结晶合金低压铸造补缩能力提供技术基础，同时，为探索低压下振动对糊状凝固合金合金的补缩机制以及进一步丰富和发展凝固控制技术奠定理论基础。

具有宽结晶凝固特点的ZL205A合金是航空航天领域广泛采用的高强铸造铝合金，是飞机与火箭上许多重要部位的关键零部件，其成形的质量直接关系到飞机与火箭的质量与安全，受到业界的广泛关注。由于宽结晶合金难于补缩的特点，导致ZL205A合金低压铸造铸件中的缩松缺陷依然十分严重。为此，研究开展了弹性波在粘弹性介质中传播的理论研究，探究了振动对ZL205A合金低压铸件补缩的影响，具体研究如下：1）建立了振动在合金凝固过程传输的基本方程；2）振动在合金凝固过程中的传播；3）探究了宽结晶合金振动补缩机理；4）研究了低压铸造中宽结晶合金振动补缩规律。上述研究取得了一系列重要的结果：（1）构建了弹性波在弹性及粘弹性变温介质中传播的热-力耦合传输模型，统一了弹性波在弹性-粘弹性-粘性介质中传播的多模型问题；（2）建立了热力耦合传输模型的高阶交错网格有限差分算法，开发了弹性波在变温变结构粘弹性复杂介质中传播的数值模拟软件，为研究振动对铸件补缩的影响提供了分析平台；（3）获得了弹性波在金属熔体中的传播和衰减规律：弹性波在非均温的金属熔体中会发生散射衰减；弹性波在金属熔体中的衰减系数随熔体温度的升高而先升高后减小，衰减系数最大的温度对应合金的枝晶搭接温度；（4）获得了振动促进低压铸件补缩的机制和补缩规律：振动对晶粒堆积结构的改变是促进宽结晶合金浆态补缩和爆发式补缩的主要原因；振动产生的附加压力和对毛细通道尺寸的改变是促进宽结晶合金枝晶间补缩的主要原因；提高保压压力，采用波导杆沿水平方向向铸件中施加大振幅和共振频率的振动能最大程度地促进低压铸造的补缩能力。上述研究所取得的成果对于推动铸件特殊外场下成形理论的进步，提高特种铸造技术具有重要的理论意义和指导实际生产的应用价值。