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알루미늄-아연-마그네슘 합금의 원자단위 투과전자현미경 관찰 기반 η1 석출물 성장 고찰
김황선,한흥남 대한금속·재료학회 2024 대한금속·재료학회지 Vol.62 No.8
Aluminum-Zinc-Magnesium (Al-Zn-Mg) alloys are extensively utilized in aerospace and automotiveindustries because of their exceptional mechanical properties and light weight. These properties of Al-Zn-Mgalloys are significantly influenced by the morphology, distribution, and size of the precipitates within the alloy,which result from the formation of numerous nanoscale precipitates. Among the various types of precipitates,η precipitates are the most representative, with the η1 variant comprising approximately 50% of the total ηprecipitates. In this study, we investigated the atomic-scale growth mechanism of η1 precipitates in Al-ZnMgalloys using high-resolution scanning transmission electron microscopy (STEM). The investigationrevealed that the growth of η1 precipitates is driven by the separation of Mg and Zn atomic columns alongthe aluminum atomic arrangement near the interface, which facilitates the stepwise growth of theprecipitates. Additionally, it was observed that a unique interfacial segregation layer forms in the directionof η1 precipitate growth, and energy-dispersive X-ray spectroscopy (EDS) confirmed that this layer is composedof Mg and Zn. These findings provide critical insights into the microscopic interactions and transformationsthat govern the precipitate formation process. This research offers valuable information for optimizing themicrostructure and enhancing the mechanical performance of Al-Zn-Mg alloys for various high-performanceapplications.
초음파 처리 활용 실시간 투과전자현미경 관찰용 금속 시편 전사 방법에 관한 연구
김황선 한국소성∙가공학회 2024 소성가공 : 한국소성가공학회지 Vol.33 No.2
Micro-electromechanical systems (MEMS) based in-situ heating holders have been developed to enable high resolution imaging of heat treatment analysis. However, unlike the standard 3 mm metal disk specimens used in the furnace-based heating holder and general transmission electron microscopy holder, the MEMS-based in-situ heating holder requires thin specimens that can be penetrated by electrons to be transferred onto the MEMS chip. Previously, focused ion beam milling was used to transfer metal specimens, but it has the disadvantage of being expensive and the risk of specimen damage due to gallium ions. Therefore, in this study, we devised a method of transferring metallic materials by ultrasonic treatment using a transmission electron microscopy specimen made by electro jet polishing. A 3mm electropolished metal disk was placed in an appropriate solution, ultrasonicated, and then drop casted. The transfer of the specimen was successful, but it was confirmed that dislocations were formed inside the specimen due to ultrasonic treatment. This study provides a novel method for transferring metallic materials onto MEMS chips, which is cost-effective and less gallium ion damaging to the specimen. The results of this study can be used to improve the efficiency of heat treatment analysis using MEMS-based in-situ heating holders.
원자단위 투과전자현미경을 활용한 알루미늄-아연-마그네슘 합금 내부 η2 석출물 성장 메커니즘 규명
김황선,한흥남 한국소성∙가공학회 2024 소성가공 : 한국소성가공학회지 Vol.33 No.1
Aluminum-zinc-magnesium alloy is a well-known alloy that is both strong and lightweight. Precipitation strengthening plays a significant role in the strength mechanism of this alloy, with nano-sized η-based precipitates being the representative precipitates. However, the growth of η precipitates can lead to a decrease in strength, necessitating research into ways to control their growth. In this study, we observed the atomic-level behavior of η2 precipitates and discovered that the precipitates grew through a combination with magnesium after a zinc segregation layer was formed around them.