Role of the local stress systems on microstructural inhomogeneity during semisolid injection
Role of the local stress systems on microstructural inhomogeneity during semisolid injection
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DOI：
10.1016/j.actamat.2021.117015
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发表时间：
2021-06-06
期刊：
影响因子：
9.4
通讯作者：
Karagadde, S.
中科院分区：
文献类型：
--
作者：
Bhagavath, S.;Gong, Z.;Karagadde, S.
高压金属压铸是一个非常动态的过程，具有广泛的冷却速率和强化压力，导致在同一铸件中同时存在广泛的固体分数和变形速率。这些工艺参数及其复杂的相互作用决定了微观结构凝固缺陷的形成。在这项研究中，快速同步辐射X射线成像实验模拟高压压铸铝合金进行调查的固相分数，加载条件和半固态流动对局部微观组织不均匀性的影响。虽然大多数现有的文献在这一领域的报告速度高达10 μ m/s的原位变形，目前的工作捕获快得多的填充和固化，在接近100 μ m/s的速度和不同的固体分数。低固相分数的半固态变形揭示了两个典型的显微组织特征：（i）粗晶粒在中间和更细的壁附近，和（ii）重熔附近的固-液界面由于Cu富集在液体中的流动。高固相分数样品的非原位扫描和数字图像相关分析揭示了基于局部应力状态、微观结构和进料的孔隙形成机制。确定了四个不同的特征：（i）活塞流，（ii）死区（致密糊状物），（iii）剪切和（iv）散装区。这些见解将被用来制定特定区域的战略，在压铸过程中的缺陷形成的数值模拟。皇冠版权所有（c）2021由Elsevier Ltd代表Acta Materialia Inc.发布。All rights reserved.
High pressure metal die casting is an extremely dynamic process with widely ranging cooling rates and intensifying pressures, resulting in a wide range of solid fractions and deformation rates simultaneously existing in the same casting. These process parameters and their complex interplay dictate the formation of microstructural solidification defects. In this study, fast synchrotron X-ray imaging experiments simulating high pressure die casting of aluminium alloys were conducted to investigate the effect of solid fraction, loading conditions and semisolid flow on local microstructural inhomogeneity. While most of the existing literature in this field reports speeds up to 10 mu m/s for in situ deformation, the present work captures much faster filling and solidification, at speeds closer to 100 mu m/s and at different solid fractions. Semisolid deformation of low solid fractions reveals two typical microstructural features: (i) coarser grains in the middle and finer ones near the walls, and (ii) remelting near the solid-liquid interface due to Cu enrichment in the liquid by the flow. Ex situ scans and digital image correlation analysis of the higher solid fraction samples reveal a porosity formation mechanism based on the local state of stresses, microstructure and feeding. Four different characteristics were identified: (i) plug flow, (ii) dead zone (densified mush), (iii) shear and (iv) bulk zones. These insights will be used to develop zone-specific strategies for the numerical modelling of defect formation during die casting. Crown Copyright (c) 2021 Published by Elsevier Ltd on behalf of Acta Materialia Inc. All rights reserved.