1.
T. Murayama
Kansai University, Japan
POTENTIAL OF DUCTILE HIGH-ENTROPY ALLOYS AS CASTING MATERIALS
2.
R. Bähr1, C. Michaelis1, S. Scharf2
1Otto von Guericke University Magdeburg, Germany
2Fraunhofer IFF Magdeburg, Germany
ALUMINIUM CASTING: PROCESSES, APPLICATIONS, QUALITY
3.
F. Zupanič, T. Bončina
University of Maribor, Faculty of Mechanical Engineering, Slovenia
DEVELOPMENT OF HEAT RESISTANT ALUMINIUM ALLOYS
1.
T. Murayama
Kansai University, Japan
POTENTIAL OF DUCTILE HIGH-ENTROPY ALLOYS AS CASTING MATERIALS
Abstract
A new approach which has been successful in designing the novel high-entropy alloys with dispersed graphite particles, showing high tensile strength and high toughness at low temperature, such as liquid nitrogen temperature (77K) is presented. Carbon was added into CrMnFeCoNi alloys in Ar atmosphere by an electric furnace. The matrix of cast alloys was fcc in all specimens. Most amount of carbon was distributed in carbides formed as primary solidification phase. The amount of carbides decreased with decreasing Cr activity. In cases that carbon activity was high, graphite particles were formed, and the amount shrinkage in casting specimens decreased. Graphite dispersed ductile high-entropy casting alloy is possible to design by controlling carbon activity and chromium activity.
Key words: carbide, CrMnFeCoNi alloy, fcc, graphite, shrinkage
2.
R. Bähr1, C. Michaelis1, S. Scharf2
1Otto von Guericke University Magdeburg, Germany
2Fraunhofer IFF Magdeburg, Germany
ALUMINIUM CASTING: PROCESSES, APPLICATIONS, QUALITY
Abstract
The driving force for improved properties, lower production cost and greater strength/ weight ratios together with demands such as reduced pollution, improved fuel efficiency and increased performance have helped aluminum alloy castings replace iron-based alloys in many applications. It is these distinctive properties why aluminum has been predominantly associated with aerospace and automotive industries.
In a typical foundry floor, several precautions are taken prior to the casting in order to achieve pore-free, high quality parts. In an aluminum product, the properties are influenced by melt treatment, casting technique and microstructure. Solidification is the stage at which the microstructure is formed. Segregation and hot tearing are among the kind of defects that can occur during solidification. Defects that are formed at the melting stage and during the handling of the melts in a casting process. All these processes occur before the stage of solidification. Undoubtedly, any defect present or created at the melting stage could be carried to the final microstructure, effectively adding to any solidification defects, and will, of course, affect the component’s life. Therefore it is apparent that the control of the quality of the product begins with the control of the quality of the melt.
The elimination of the hydrogen in molten aluminum (degassing) is crucial for producing high-quality castings. There are several degassing methods that have been studied in the past few decades, including re-melting degassing, vacuum degassing, ultrasonic degassing, spray degassing, rotary impeller and tablet degassing.
At first a compendium of vacuum technology from one of the greatest technical inventions of the 17th century by Otto von Guericke to its application in today’s foundry industry will be given. In addition the importance of impeller treatment of aluminium melts and their framework conditions will be discussed in more detail. In particular the effects of the treatment and their influence pore formation, distribution and morphology are illustrated.
Adjoined to this a digression on the casting quality with illumination of the most striking casting failure porosity, which can be determined by the use of X-ray computed tomography three- dimensional. According to this X-ray computed tomography is applied to aluminium alloy to characterize the size and morphology of casting porosity. Furthermore the usefulness of X-ray microtomography to study the influence of the casting microstructure upon the mechanical properties of an aluminium alloy are discussed.
Key words: aluminum, melt treatment, vacuum, degassing, quality, pores, mechanical properties
3.
F. Zupanič, T. Bončina
University of Maribor, Faculty of Mechanical Engineering, Slovenia
DEVELOPMENT OF HEAT RESISTANT ALUMINIUM ALLOYS
Abstract
The production of Al-alloys strongly increases due to their low density, high specific modulus and strength. These properties can significantly reduce CO2 emissions and energy consumption in transportation and construction. The conventional Al-alloys possess rather low heat resistance as loose very rapidly their strength when heated above 250 °C. The demands for the high heat-resistant Al-alloys have been increased recently. Therefore, several new alloys have been investigated and developed over the last years. The most important approaches are through the application of modern technologies; such as melt-spinning and extrusion of ribbons by the development of Al-Mg-Sc-Zr alloys, gas atomisation and sintering of nanoquasicrystalline strengthened alloys and additive technologies (selective laser melting). There are several investigations regarding heat resistance of casting alloys, such as Al-Si and Al-Cu-Si, and wrought alloys. The heat resistance is improved by the formation of the temperature resistant phases, which can be formed during solidification or heat treatment. In the article different approaches will be presented, with the focus on the casting alloys.
Key words: aluminium, heat resistance, strength, creep