Sub-Liquidus Casting (SLC)

요약:

Sub-Liquidus Casting is one of many known semi-solid metal technologies and holds great value offering grain refinement accompanied by proper control of melt temperature and cooling rate.
Some key advantages include improved tool life and time savings through quicker solidification.

Semi-solid metal (SSM) technology is different from the conventional forming processes which uses either solid or liquid metals as the starting material. This process deals with slurries, which in principle, can be produced in any material systems where liquid and solid phases coexist over a freezing range. The SSM process has advantages over other casting processes which are associated with less porosity and shrinkage voids, lower processing temperature and shorter time, less mold erosion, faster cycle time and longer die life.

Semisolid processing consists of two or three stages. First, a globular structure within the semisolid alloy is created. Then the semisolid slurry is used either directly for applications that require slurry (rheocasting) to form a component with near-net shape or be solidified as billets for later reheating during thixocasting.

There is a wide range of (SSM) processes patented or under investigation within research and development centers worldwide.

One of them is the Sub-Liquidus Casting (SLC) process. The process was developed by THT Presses Inc., USA, and explores a phenomenon of grain refinement accompanied by proper control of melt temperature and cooling rate.



Figure 1: 400t THT press machine

In fact, the successful process cycle can only be implemented if good grain refinement is achieved in the molten alloy supplied to the machine. The grain refined material is poured into the shot sleeve at temperatures just above liquidus and cooled to a semisolid state before transfer to the mold. For practical reasons, a superheat of 5–10°C is used to compensate for heat losses during alloy transfer from the furnace to the shot sleeve.

The slurry is developed within the shot sleeve, which means that no slurry processing equipment is required outside of the casting machine (Figure 2). For aluminum alloy A356 the temperature in the chamber before injection is between 570°C and 590°C. For proper grain refinement, fine rosettes transform into globules within seconds while coarse dendrites in poorly refined alloy would require more time to transform into globular features.

Although the machine features alone do not constitute the entire process, the specific features allow its proper implementation. They include large and shallow shot diameter and short stroke as well as a unique gate plate. The shot piston and sleeve wall temperatures are controlled to extract the heat primarily through the piston and less through the shot sleeve walls. The melt is transferred to the die cavity at very low velocity of the order of 1 m/s–2 m/s through a gate plate with multiple gates.



Figure 2: The concept of sub-liquidus casting (SLC) developed by THT Presses Inc.

The advantages and requirements of sub-liquidus casting (SLC) are summarized as follows:

SLC advantages:
1) Breakway gates
2) Less sensitive to:
• Microstructural effects on properties
• Metal flow in die cavity and entrapment of bubbles
• Directional solidification
3) Less thermal input to die (~50% less)
• Longer tool life (2-5 times)
• Quicker solidification

SLC Requirements:
1) Grain refinement
2) Melt temperature (in furnace)
3) Melt cooling in shot sleeve
4) Time to develop slurry structure
5) Melt flow into die cavity



Figure 3: Typical A356 alloy SLC microstructure (x100)


References

1. S. Nafizi: Effects of grain refining and modification on the microstructural evolution of semi-solid 356 alloy, University of Quebec at Chicoutimi, April 2006, Accessed Nov 2016

2. F.Czerwinski: Magnesium Injection Molding, Springer, 2008, ISBN-13: 978-0-387-72399-0 e-ISBN-13: 978-0-387-72528-4

3. A.Forn, M.T.Baile, S.Menargues, I.Espinosa: Corrosion resistance improve by hard anodize A356 aluminium alloy by subliquidus casting, OAI, 2008

4. Sub-Liquidus Casting: Process Concept and Product Properties, ss, Accessed Nov 2016

기술 자료 검색

검색할 어구를 입력하십시오:

검색 범위

본문
키워드

머릿글
요약

Total Materia는 다양한 나라와 규격에 따른 수천개의 주조 재료에 대한 정보를 포함하고 있습니다.

재질의 화학적 조성, 기계적 특성, 물리적 특성, 고급 물성 데이터 등의 전체적인 특성 정보들을 어디서든 검토하실 수 있습니다.

고금 검색 내 규격 설명 기능을 이용하여, 규격 내 재질에 설명된 키워드를 통해 재질을 검색하실 수 있습니다.

검색 범위 좀 더 줄이기를 원하신다면 국가/규격과 같은 다른 조건을 지정할 수 있습니다.

검색 버튼을 클릭합니다.


선택된 정보에 부합하는 일련의 재질이 검색됩니다.


결과 리스트에서 재질을 선택하시면, 일련의 규격 사양 소그룹이 나타납니다.

여기에서 선택한 재질의 특정 특성 데이터를 검토하실 수도 있고, 강력한 상호 참조 표를 이용하여 유사 재질이나 등가 재질을 검토하는 것 또한 가능합니다.


예를 들어, 소그룹 내 화학적 조성 링크를 클릭하시면, 재질의 화학적 조성 데이터를 검토하실 수 있습니다.

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