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Evaluation of heat transfer coefficients during upward and downward transient directional solidification of Al–Si alloys

机译：Al-Si合金向上和向下瞬态定向凝固过程中的传热系数评估

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摘要

Aluminum alloys with silicon as a major alloying element consist of a class of alloys which provides the most significant part of all shaped castings manufactured. This is mainly due to the outstanding effect of silicon in the improvement of casting characteristics, combined with other physical properties such as mechanical properties and corrosion resistance. In general, an optimum range of silicon content can be assigned to casting processes. For slow cooling rate processes (sand, plaster, investment), the range is 5 to 7 wt%; for permanent molds, 7 to 9%; and for die castings, 8 to 12%. Since most casting parts are produced considering there is no dominant heat flow direction during solidification, it seems to be adequate to examine both upward and downward growth directions to better understand foundry systems. The way the heat flows across the metal/mold interface strongly affects the evaluation of solidification and plays a remarkable role in the structural integrity of castings. Gravity or pressure die casting, continuous casting, and squeeze casting are some of the processes where product quality is more directly affected by the interfacial heat transfer conditions. Once information in this area is accurate, foundrymen can effectively optimize the design of their chilling systems to produce sound castings. The present work focuses on the determination and evaluation of transient heat transfer coefficients from the experimental cooling curves during solidification of Al 5, 7, and 9 wt% Si alloys. The method used is based on comparisons between experimental data and theoretical temperature profiles furnished by a numerical solidification model, which applies finite volume techniques. In other words, the resulting data were compared with a solution for the inverse heat conduction problem. The necessary solidification thermodynamic input data were obtained by coupling the software ThermoCalc Fortran interface with the solidification model. A comparison between upward and downward transient metal/mold heat transfer coefficients is conducted.
机译：以硅为主要合金元素的铝合金由一类合金组成，这些合金提供了所制造的所有异型铸件中最重要的部分。这主要归因于硅在改善铸造特性方面的杰出作用，并结合了其他物理性能，例如机械性能和耐腐蚀性。通常，可以将最佳硅含量范围分配给铸造工艺。对于慢速冷却过程（砂，灰泥，投资），范围为5至7 wt％；对于永久性模具，为7至9％；对于压铸件，则为8至12％。由于大多数铸造零件的生产都考虑到凝固过程中没有主要的热流向，因此似乎可以同时检查向上和向下的生长方向以更好地了解铸造系统。热量流过金属/模具界面的方式极大地影响了凝固的评估，并在铸件的结构完整性中发挥了重要作用。重力或压铸，连续铸造和挤压铸造是其中界面传热条件更直接影响产品质量的某些过程。一旦该区域的信息准确，铸造厂便可以有效地优化其冷却系统的设计，以生产出优质的铸件。本工作着重于在Al 5、7和9 wt％的Si合金凝固过程中根据实验冷却曲线确定和评估瞬态传热系数。所使用的方法基于实验数据与数值凝固模型提供的理论温度曲线之间的比较，该模型采用有限体积技术。换句话说，将所得数据与逆导热问题的解决方案进行比较。通过将软件ThermoCalc Fortran接口与固化模型耦合，可以获得必要的固化热力学输入数据。进行向上和向下瞬态金属/模具传热系数之间的比较。

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