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1.
S. Ramrattan1, L. Wells1, R. Tuttle2, J. Medved3
1 Western Michigan University, US;
2 Saginaw Valley State University, US;
3 University of Ljubljana, Slovenia
REFRACTORY COATED SURFACE CHARACTERIZATION FOR STEEL USING DISC- SHAPED CHEMICALLY BONDED SAND SPECIMENS – PART II
Abstract
Steel castings are returning to the U.S. Metal Casting Industry from the Global Market Place. Chemically bonded sand systems are an important and growing part of foundry technology and their interaction at the mold-steel interface is in question based on a study - Part I. The qualitative changes in surface quality found at uncoated as-casted steel/chemically bonded sand interfaces (Part I) may require refractory coating (wash) technology to warrant improvement. With today’s emphasis on near-net-shape steel castings, and with ever more stringent casting dimensional reproducibility requirements, there is a need to quickly and affordably characterize as-cast surface quality as a function of the refractory coated chemically bonded sand system. Four refractory coatings designed for steel castings were applied to disc-shaped specimens (cores) by industry using the application techniques used in normal foundry production. A small, simple, and practical casting trial using disc-shaped specimen cores was developed at Western Michigan University (WMU). The test allows several core specimens to be wetted simultaneously from a known steel head pressure, temperature, and chemistry. The casting trials were conducted at Saginaw Valley State University (SVSU) and results show that various refractory coated chemically bonded sand systems provide different ascast steel surfaces. Results show that new refractory coatings technology can provide a superior as-cast surface quality to silica and ceramic sands in a steel casting. Still, adequate refractory coatings are required to reduce and/or eliminate sand/binder burn-on. Finally, the refractory coatings can affect the shakeout/collapsibility of the chemically bonded sand system.
Keywords: burn-on (to include terms such-as burn-in, penetration, and adhering coating), disc-shaped specimens, casting trial, chemical sand binder, refractory coating, surface roughness
2.
M. PETRIČ, B. ZEKA, P. MRVAR, B.LESKOVAR , B.MARKOLI
University of Ljubljana (SI)
DEVELOPMENT OF AlSi7Mg ALLOY WITH ADDITIONS OF Li
Abstract
Aluminium alloys with lithium additions have been known to the world for several decades. The main advantage of the Li addition is the reduced alloy density and increased mechanical properties, especially the modulus of elasticity. Increased mechanical properties are mainly caused by precipitation hardening of the metastable δ’ phase (Al3Li). The main difficulty of Al- Li alloys is Li reactivity where its tendency to form oxide is very high and can reduce different metal oxides and water. At these reactions it can form gases especially hydrogen which can cause gas porosity. Similar problems are met at reactions with moulding materials where reaction products can influence casting quality.
In the current work the investigation of Li additions to the cast AlSi7Mg alloy is treated. The addition of Li amounts to 1 wt.%. Different moulding materials such as Cronning sand mixture, CO2 sand mixture, silicate brick, graphite and steel mould were tested to determinate the surface quality of a casting and the amount of reaction products. The best results without reaction products were given by graphite and steel mould. At the same time a simple thermal analysis was performed to explain the solidification course of the new alloy in correlation with thermodynamic equilibrium calculations. Optic, scanning electron microscopy with EDS analysis and XRD analysis were used to identify microstructural constituents of which the AlLiSi phase contained Li. Mechanical tests showed that natural ageing occurs, and hardness is increased, indicating that the Al3Li phase precipitates.
Key words: aluminium alloys, microstructure, lithium, mechanical properties.
3.
Z. Zovko Brodarac, T. Rupčić, F. Kozina, D. Mašinović,
University of Zagreb, Faculty of Metallurgy, Sisak (CRO)
INFLUENCE OF THE Alsi12 ALLOY INOCULATION ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES DEVELOPMENT
Abstract
Due to a wide range of favourable properties, aluminium alloys found their application in almost all industrial branches. The potential of improving usage properties has been recognized through the forming of favourable intermetallic in mutual interaction of numerous alloying elements such as silicon, copper or magnesium, along with trace elements such as iron and manganese. Other important elements such as titanium, boron, strontium or sodium are intently added through targeted melt treatment in order to improve the solidification path by increasing the nucleation potential and therefore changing morphology. In consideration of the casting technology parameters which influence the cooling / solidification rate also represents the base for changing the microstructure and final quality of the casting. The synergy activity of the alloying and/or trace elements and their interaction and technological parameters of casting process is of great importance in consideration of alloy applicability. This investigation deals with EN AC AlSi12 (EN AC 44100) eutectic alloy with narrow solidification interval, intended for rapid cooling/solidification technology such as high pressure casting (HPDC). The effect of a different mode of AlSi12 alloy melt treatment on microstructure and mechanical properties was monitored as a quality insurance. Applied melt treatment mode consists of modification of eutectic with addition of AlSr10 master alloy in all investigated cases. The difference in melt treatment mode was in targeted addition of AlTi5B master alloy. The hypothesis of the examination is based on the assumption that targeted melt treatment can influence the solidification manner, development of microstructural characteristics and finally achieving mechanical properties of the alloy in accordance to corresponded casting geometry and/or technology application.
Key words: AlSi12 alloy, inoculation, modification, microstructure, mechanical properties