15. - 17. 5. 2013, Brno, Czech Republic, EU INFLUENCE OF RECYCLING OF CAST ALUMINIUM ALLOYS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES Marek BŘUSKA, Petr LICHÝ, Michal CAGALA, Jaroslav BEŇO, Miroslav BODROG, David ŽÁČEK VŠB – TU Ostrava, 17. listopadu 15/2172, 708 33 Ostrava, Czech Republic, EU, marek.bruska@seznam.cz Abstract Considering the rising prices of materials, the enterprises engaged in processing of alloys and in the manufacture of castings seek for ways of production cost reduction. One way of saving is consists in utilisation of recycled materials or in re-melting of foundry returns. This study is focused on evaluation of mechanical and thermo-mechanical properties of the Al-Cu alloy (RR.350) at multiple re-melting in cast condition. The research team focused on a change of following properties: tensile strength, hardness, micro- hardness, change of chemical composition of the alloy, change of the microstructure of the alloy and dilatation after re-melting. Keywords: tensile strength, hardness, micro-hardness, change of the microstructure of the alloy, dilatation after re-melting 1. INTRODUCTION Importance of alloys of non-ferrous metals as structural materials is currently growing thanks to their good mechanical and thermo-mechanical properties, low specific mass and possibility of thermal processing enhancing utility properties of the alloy. Thanks to the above-mentioned properties the non-ferrous metals alloys replace in various industries the iron-based alloys [1]. Use of these alloys is very important in machine- building industry: e.g. for heat exchangers, equipment for oil refining, distillation apparatuses, pumps and piping. The largest use is, however, still in the transport industry, where they are used mainly for the components exposed to heat, such as cylinder heads, gears or aerospace components. This trend was intensified by the current economic crisis. One of the ways is to use recycled material or to re-melt foundry returns. 1.1. Alloy RR.350 Some of the most commonly used alloys are the aluminium based alloys. We focused on the Al-Cu based alloy of the type RR.350 due to its favourable properties, low mass, minimal dilatation and its ability to withstand higher temperatures up to 350 °C [2]. The RR.350 alloy is used for the heat-stressed castings and for the castings exposed to higher pressures. This alloy is widely used not only in the automotive industry, and it is used in heat-treated state when its properties achieve the highest values. Our research is focused on the evaluation of mechanical and thermo-mechanical properties of this alloy after its multiple re-melting in the cast state. Chemical composition of the alloy used for the experiment is given in Table 1. The alloy is rich in additive elements, which enhance its (mechanical) properties. The alloy itself has very poor casting properties and impaired resistance to corrosion. It is difficult to ensure its risering as it creates dispersed shrink holes and also cavities of all kinds.