Low Frequency Electromagnetic Casting of Al Alloys

요약:

In the Low Frequency Electromagnetic Casting process the mold is surrounded by a coil powered by an alternating current to endue an electromagnetic field.
One of the biggest advantages of using the LFEC process in comparison to conventional casting processes is a distinct improvement in the microstructure with LFEC ingots producing a very fine equiaxed grain structure.

In a typical (semi) continuous casting process, liquid material comes from a furnace and flows down from a ladle into a tundish and is continuously melted from there into a vertical water-cooled chill mold while a solid shell of the cast material, which contains melt in its center, is simultaneously extracted from the bottom of the chill-mold.

The mold has to be an excellent thermal conductor in order to extract heat rapidly from the melt. During the passage of the material through the mold, a solid shell must be formed that is stable enough to keep its shape unchanged while it is continuously extracted vertically from the mold.

When the material shell leaves the chill-mold it enters a series of cooling zones. The cooling medium is water, which is sprayed directly on the entire periphery of the casting. The principle of semi-continuous casting is demonstrated in Figure 1 (it applies well to continuous casting also). This is the conventional casting process, often called direct-chill casting (abbreviated and used in the text as DC).

In Low Frequency Electromagnetic casting (LFEC), the mold is surrounded by a coil powered by an alternating current. The current induces an electromagnetic field in the system. Figure 2 shows schematics of the LFEC and direct-chill (DC) processes. As will be seen, the presence of an electromagnetic field significantly alters the process.



Figure 2: A cross-section schematic of the LFEC (left) and DC (right) processes. See [4] for details.

In the paper of J.Cui, H.Zhang and H.Nagaumi the analyzed the effects of low frequency electromagnetic field casted of AA7055 aluminum alloy is studied on the macro-physical fields (flow field, temperature field and stress-strain field) during the semi-continuous casting process of aluminum alloys, the microstructure and crack in the ingots by the numerical and experimental methods.

Comparison of the results for the macro-physical fields in the LFEC process compared with that in the conventional DC casting process indicate the following characters due to the application of electromagnetic field: a vigorous forced convection of the melt; an entirely changed direction of melt flow; a remarkably increased velocity of melt flow; a uniform distribution of temperature; a decreased gradient of temperature; the elevated isothermal lines; the reduced sump depth; the decreased stress and plastic deformation.

Furthermore, the microstructure of the ingot is refined remarkably and the crack in the ingots is eliminated in the LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field.



Figure 1: Microstructure of LFEC (a) and DC (b) ingots

Figure 1 (a) and (b) show the microstructure of the ingots cast in the conventional DC casting and LFEC processes, respectively. It is observed from this figure that the microstructure of the ingots cast in the conventional DC casting process is usually coarse dendritic structure in the absence of the master alloy, but that in the LFEC process is very fine equiaxed grain structure.


References

1. U. Žunkovič: Low-frequency electromagnetic casting, Final year seminar, University of Ljubljana, Faculty of Mathematics and Physics, October 2012,

2. J. Cui, H. Zhang, H. Nagaumi: A New Approach to Producing AA7055 Aluminum Alloy Slab Ingots, Proceedings of the 12th International Conference on Aluminium Alloys, September 5-9, 2010, Yokohama, Japan, p.646-651

기술 자료 검색

검색할 어구를 입력하십시오:

검색 범위

본문
키워드

머릿글
요약

Total Materia는 다양한 나라와 규격에 따른 금속학 이미지에 대한 정보를 포함하고 있습니다.

메뉴 표시줄에 특별히 디자인된 금속학 탭을 이용하여, 금속학 데이터가 포함된 관심 재질을 리스트에서 선택하실 수 있습니다.

또한 금속학 데이터는 표준 빠른 검색을 통해 찾을 수 있으며 규격 내 소그룹 페이지를 통해 이용 가능한 관련 자료들이 표시됩니다.

재질명을 '재질'창에 입력하신 후 규격을 알고 계신다면 규격을 선택하고 '검색' 버튼을 클릭합니다.


미세 구조에 대한 일반적인 정보가 관련 관심 재질의 화학 조성과 함께 출력됩니다.


구조의 세부 범위를 보여주는 여러 배율에서의 이미지가 가능하다면 제공됩니다.

다양한 조건을 선택할 수 있으며, '조건 선택' 메뉴를 사용하여 다양한 공정 및 열처리에 따른 금속학 이미지를 보여줍니다.



Total Materia 데이터베이스를 사용해 보실 수 있는 기회가 있습니다. 저희는 Total Materia 무료 체험을 통해 150,000명 이상의 사용자가 이용하고 있는 커뮤니티로 귀하를 초대합니다.