Theories on fluidity of alloys based on the solidification mode are not satisfactory in describing fluidity of alloys under high-pressure die casting (HPDC) conditions. To understand the flow-choking mechanisms under HPDC conditions, microstructure in the fluidity test coupons made using a 125-ton HPDC machine was characterized. Pre-solidified dendrites (PSDs), or externally solidified crystals (ESCs), which were formed in the shot sleeve, were found in the runners as well as in the fluidity casting. Surprisingly, a large amount of PSDs are collected in the runner adjacent to the in-gate, forming a PSD core with a thin layer of PSD-less or PSD-free region near the surfaces of the runner due to Magnus effect. Analytical calculations were performed to estimate the pressure drop for molten aluminum flowing through the mushy PSD zone. The results indicate that the pressure drop is comparable to the maximum pressure that was used for injecting molten metal to fill the casting. When the pressure drop is equal to the pressure driving the mold filling, the metal ceases to flow. Thus, it is the PSDs that are responsible for the choking of mold filling either mechanically at the in-gate or providing a pressure drop high enough to resistant fluid flow.

中文翻译：

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高压压铸条件下合金的流动性：节流机制

基于凝固模式的合金流动性理论在描述高压压铸（HPDC）条件下合金的流动性时并不令人满意。为了了解 HPDC 条件下的流动阻塞机制，对使用 125 吨 HPDC 机器制成的流动性测试试样的微观结构进行了表征。在流道和流动性铸件中发现了在压射套筒中形成的预凝固枝晶 (PSD) 或外部凝固晶体 (ESC)。令人惊讶的是，大量 PSD 被收集在与栅极相邻的流道中，由于马格努斯效应，在流道表面附近形成了具有 PSD 少或无 PSD 区域的薄层的 PSD 核心。进行分析计算以估计熔融铝流过糊状 PSD 区域的压降。结果表明，压降与用于注入熔融金属以填充铸件的最大压力相当。当压降等于驱动模具填充的压力时，金属停止流动。因此，PSD 负责在浇口内机械地阻塞模具填充，或者提供足够高的压降以阻止流体流动。