Numerical modelling and experimental validation of the effect of ultrasonic melt treatment in a direct-chill cast AA6008 alloy billet
Numerical modelling and experimental validation of the effect of ultrasonic melt treatment in a direct-chill cast AA6008 alloy billet
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DOI：
10.1016/j.jmrt.2021.03.061
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发表时间：
2021-03
期刊：
影响因子：
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通讯作者：
T. Subroto;G. Lebon;D. Eskin;Ivan Skalicky;Dan Roberts;I. Tzanakis;K. Pericleous
中科院分区：
文献类型：
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作者：
T. Subroto;G. Lebon;D. Eskin;Ivan Skalicky;Dan Roberts;I. Tzanakis;K. Pericleous
在这项工作中，我们研究了超声空化熔体处理(UST)对AA6008铝合金直接激冷(DC)铸造过程中的温度分布、熔池形状和组织的影响。两个152 mm直径的铸坯，一个在热顶进行UST处理(UST-DC铸造)，另一个不进行处理(常规DC铸造)。为了研究铸坯的温度分布，对两种铸坯的多点温度进行了测量。通过在浇注过程中向水池中浇注锌，可以直观地显示水池轮廓。通过对铸坯晶粒度的测量，分析了铸坯的显微组织。通过对铸坯温度的测量，验证了直流浇注和UST-DC浇注的数值模型，实验结果与数值模型吻合较好。结果表明，用热电偶测量的水坑剖面比用锌示踪测量的水池剖面更准确，更不易解释。数值模拟结果表明，在石墨环上方20 mm处的热顶上施加UST，降低了液线等温线，但不影响固相线等温线，导致过渡区较薄。颗粒组织分析表明，在给定的声纳电极位置，用UST实现了组织细化。铸坯中心的晶粒细化作用最强，平均晶粒度比未加UST时小50%。根据已知的UST机制，即枝晶碎裂和形核基质的解聚，对结果进行了讨论。
In this work, we study how ultrasonic cavitation melt treatment (UST) affects the temperature distribution, sump profile, and resulting microstructure in the direct-chill (DC) casting of an AA6008 aluminum alloy. Two 152 mm diameter billets were cast; one was treated with UST (UST-DC casting) in the hot top while the other was not (conventional DC casting). To investigate the temperature distribution, temperature was measured at multiple points in both billets. The sump profile was visualized by pouring Zn into the sump during casting. The microstructure was analyzed by measuring the grain size of as-cast billets. A numerical model of DC casting and UST-DC casting has been validated with the temperature measurements across the billets, and the experimental results agrees well with the numerical model. It is found that the sump profile quantification with thermocouple measurements is more accurate and less prone to interpretation than with Zn tracing. Numerical simulation results show that UST application in the hot top with sonotrode position at 20 mm above the graphite ring level depresses the liquidus isotherm but does not affect the solidus isotherm, resulting in a thinner transition region compared with conventional DC casting. Grain structure analysis verifies that structure refinement with UST has been achieved at the given sonotrode position. The strongest grain refinement was at the center of the billet with the average grain size 50% smaller than that without UST. The results are discussed in terms of the known mechanisms of UST, i.e. dendrite fragmentation and deagglomeration of nucleating substrates.