Validation of a systematic approach to modeling spray quenching of aluminum alloy extrusions, composites, and continuous castings
Validation of a systematic approach to modeling spray quenching of aluminum alloy extrusions, composites, and continuous castings
复制标题
铝合金挤压件、复合材料和连铸件喷雾淬火建模系统方法的验证
DOI：
--
复制
发表时间：
1997
期刊：
影响因子：
--
通讯作者：
S. L. Ehlers
中科院分区：
文献类型：
--
作者：
D. D. Hall;I. Mudawar;R. E. Morgan;S. L. Ehlers
铝合金在高温挤压工艺后的最佳冷却可抑制金属间化合物的沉淀，并使零件在随后的时效硬化工艺后能够拥有最大的强度和硬度。快速淬火可以抑制沉淀，但会导致形状复杂的零件产生较大的空间温度梯度，从而导致变形、开裂、高残余应力和/或机械性能不均匀。相反，缓慢冷却可显着减少或消除这些不良情况，但会产生大量沉淀，导致强度低、软点和/或耐腐蚀性低。这项研究提出了一种针对任何形状的挤压件定位和操作多个喷嘴的系统方法，从而实现均匀、快速的冷却以及优异的机械和冶金性能。通过测量各种工业喷嘴整个喷雾场的喷雾流体动力学参数（体积喷雾通量、平均液滴直径和平均液滴速度）的分布，编制了喷雾喷嘴数据库。喷雾传热相关性将局部喷雾流体动力学参数与表面经历的每个沸腾状态中的传热速率联系起来，定义了淬火过程数值模型中的空间不均匀边界条件，该模型还解释了相邻喷雾场之间的干扰。针对对最终机械性能具有关键影响的高温沸腾状态，制定了新的关联式，可提供更高的精度和更少的计算时间。淬火系数技术将预测的热历史与挤压过程中发生的冶金转变相关联，以预测硬度分布。通过将模型预测与 L 形 Al 2024-T6 挤压件与多次重叠喷水淬火的温度响应（以及人工时效后的硬度）进行比较，证明了这种独特方法的有效性。本文报告的验证研究的结论是探索应用淬火技术来提高挤压金属基复合材料（例如 SiCp/Al 6061 和铸造合金）性能的可能性。
Optimal cooling of aluminum alloys following the high- temperature extrusion process suppresses precipitation of intermetallic compounds and results in a part capable of possessing maximum strength and hardness after the subsequent age- hardening process. Rapid quenching suppresses precipitation but can lead to large spatial temperature gradients in complex- shaped parts, causing distortion, cracking, high residual stress, and/or nonuniform mechanical properties. Conversely, slow cooling significantly reduces or eliminates these undesirable conditions but allows considerable precipitation, resulting in low strength, soft spots, and/or low corrosion resistance. This study presents a systematic method of locating and operating multiple spray nozzles for any shaped extrusion such that uniform, rapid cooling and superior mechanical and metallurgical properties are achieved. A spray nozzle data base was compiled by measuring the distribution of spray hydrodynamic parameters (volumetric spray flux, mean drop diameter, and mean drop velocity) throughout the spray field of various industrial nozzles. Spray heat transfer correlations, which link the local spray hydrodynamic parameters to the heat transfer rate in each of the boiling regimes experienced by the surface, defined the spatially nonuniform boundary conditions in a numerical model of the quenching process that also accounted for interference between adjacent spray fields. New correlations, offering increased accuracy and less computational time, were formulated for the high- temperature boiling regimes which have a critical influence on final mechanical properties. The quench factor technique related predicted thermal history to metallurgical transformations occurring within the extrusion to predict hardness distribution. The validity of this unique approach was demonstrated by comparing model predictions to the temperature response (and hardness after artificial aging) of an L- shaped Al 2024- T6 extrusion to quenches with multiple, overlapping water sprays. The validation study reported herein concludes by exploring the possibility of applying quenching technology to improving the properties of extruded metal- matrix composites such as SiCp/Al 6061 and cast alloys.