As-Cast Structure and Temperature Field of Direct-Chill Cast 2024 Alloy Ingot at Different Casting Speeds
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JMEPEG https://doi.org/10.1007/s11665-020-05140-x
As-Cast Structure and Temperature Field of Direct-Chill Cast 2024 Alloy Ingot at Different Casting Speeds Xudong Liu
, Qingfeng Zhu, Tao Jia, Zhihao Zhao, Jianzhong Cui, and Yubo Zuo (Submitted June 17, 2020; in revised form August 5, 2020)
The ingot was prepared at different casting speeds, and temperature measurements were taken during the direct-chill (DC) casting process. The results showed that the grain size of the equiaxed grains decreases, the volume fraction of the floating grains increases, and the negative centerline segregation becomes more serious as the casting speed increases. Moreover, the vertical widths and the cooling rates of different regions during the solidification process were analyzed through temperature measurements. At the casting speed of 50 mm/min, the vertical widths of the transition, slurry and mushy regions in the ingot center are relatively small (51, 15, and 36 mm, respectively). As the casting speed increases to 65 mm/min, the vertical widths of the transition, slurry, and mushy regions in the ingot center increase to 70, 29, and 41 mm, respectively. The increase in the vertical width of the slurry region is considered to be the main reason for the increase in the volume fraction of the floating grains. Besides, as the casting speed increases, the cooling rate in the mushy region and the region above the liquidus increases, so the grain size of equiaxed grain decreases. Keywords
as-cast structure, casting speed, direct-chill casting, macrosegregation, temperature field
1. Introduction Direct-chill (DC) casting process for aluminum alloy has been developed for about 90 years since it was invented in the 1930s and it is still the main method of wrought aluminum alloy production. The as-cast structure has a great influence on the quality of the final product, and a fine, uniform, and castingdefects free as-cast structure is usually desired. However, the solidification mode of DC casting is to form a solid shell first under the mold and then solidify inward gradually under the secondary cooling water. Therefore, technical challenges still exist in the high-quality ingot production, such as macrosegregation, uneven microstructure, and hot tearing (Ref 1-4). During the DC casting process, the sump can be defined as liquid melt region and the transition region. The transition region is the region between the liquidus and solidus isotherms, which can be further divided into slurry region (the region between the liquidus and coherency isotherms) and the mushy
Xudong Liu, Qingfeng Zhu, Jianzhong Cui, and Yubo Zuo, Key Lab of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang, PeopleÕs Republic of China; and College of Materials Science and Engineering, Northeastern University, Shenyang, PeopleÕs Republic of China; Tao Jia, State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang, PeopleÕs Republic of China; and College of Materials Science and Engineering, Northeastern Univ
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