Abstract For understanding the processing-microstructure-properties correlation of high pressure die casting (HPDC) AZ91D alloy, 3D reconstruction was carried out to characterize the microstructural morphologies of castings produced by four designed HPDC processes. The influence of different parameters (vacuum, slow-shot speed, fast-shot speed) on porosity volume and morphology, defect band width and average externally solidified crystals (ESCs) size of castings were systematically studied. Microstructural characterization revealed that the defect band width was strongly related with the size and quantity of ESCs, rather than the porosity volume. Meanwhile, ESCs were mainly influenced by the slow-shot speed in shot sleeve (ESCs growth time) and fast-shot speed into the die cavity (shear stress of melt flow). Tensile fracture revealed that cracks easily propagated within the defect bands due to the accumulated ESCs and connected irregular pores, while the cracks were restrained in center zone. The mechanical properties of HPDC castings was inversely proportional to the defect band width, and is not dependent on the average volume fraction porosity.

中文翻译：

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高压压铸镁合金3D缺陷带形貌与力学性能的相关性

摘要 为了了解高压压铸 (HPDC) AZ91D 合金的加工-显微组织-性能相关性，进行了 3D 重建以表征由四种设计的高压压铸工艺生产的铸件的显微组织形态。系统研究了不同参数（真空度、慢射速度、快射速度）对铸件孔隙体积和形貌、缺陷带宽度和平均外部凝固晶体（ESC）尺寸的影响。微观结构表征表明，缺陷带宽度与 ESC 的大小和数量密切相关，而不是孔隙体积。同时，ESCs主要受压射套筒内慢射速度（ESCs生长时间）和快速射入模腔速度（熔体流动剪切应力）的影响。拉伸断裂表明，由于聚集的ESCs和连接的不规则孔隙，裂纹容易在缺陷带内扩展，而裂纹在中心区被抑制。HPDC 铸件的机械性能与缺陷带宽度成反比，并且不依赖于平均体积分数孔隙率。