PSI - Issue 13

Lenka Kuchariková et al. / Procedia Structural Integrity 13 (2018) 1577–1582 Lenka Kuchariková / Structural Integrity Procedia 00 (2018) 000 – 000

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% of all the weight savings of cars is reached by application of aluminium materials, Das (2010). Production of aluminium casts from aluminium wastes and scraps requires less than 6 % of the energy of aluminium production from bauxite mining, Das (2010) and Zafar (2017). For the aluminium industry, it is appropriate to identify, develop and implement all technologies that will optimize the benefits of recycling because the automotive industry is the second-largest user of recycled aluminium. Nowadays, about 90 % of recycled aluminium alloys are used for transport and construction applications. The advantage is that the secondary aluminium can have the same properties as the primary. However, the waste and scrap alloys can lead to formation of microstructural components, which decrease the properties of aluminium castings, Zafar (2017) and Kuchariková et al. (2016a). The major group of aluminium material for casting applications is series 4xxxx (Al-Si). The quality of the recycled Al-Si casting alloys is considered to be a key factor in selecting an alloy casting for a particular engineering application. There is a need to control formation of microstructural components and their effect on properties of aluminium castings. Based on the Al-Si system, the main alloying elements are silicon (Si), copper (Cu) or magnesium (Mg) and certain amount of iron (Fe), manganese (Mn) and more, that are present either accidentally, or they are added deliberately to provide special material properties. Both iron (max. 0.05 wt. %, 0.025 atom. %) and silicon (max. 1.5 at. % at the eutectic temperature - and the solubility of silicon increases with temperature to 0.016 % Si at 1190 °C) have a very low solubility in aluminium, Slagsvold (2011). The content of iron in aluminium alloys depends on type: primary or secondary; the primary typically contains between 0.02 and 0.15 wt. % iron, (average being 0.07 to 0.10 %). Those contents depend on the quality of the incoming ore and the control of the various processing parameters and other raw materials. Typical secondary Al-Si alloys usually contain much lower Fe levels of 0.25 to 0.8 wt. %, (0.4 – 0.7 % are the most common values). Depending on the alloy composition, the cooling rate and crystallization conditions, the elements Fe, Cu, Mg, Mn, Si and other present in an aluminium alloy, will form intermetallic (secondary) phases, Mrówka (2011); Kral (2005); Rios et al. (2003). It is well-known that in aluminium alloys mechanical properties and fracture mechanisms are strongly affected by the secondary dendrite arm spacing (SDAS), the morphology and distribution of eutectic Si particles and the secondary phases, Kobayashi (2000). During the exploitation of the automobile components, the stress states, damage modes and fracture mechanisms are different at different locations on the components. Everything depends on material's microstructure. Thus, it is necessary to investigate the fracture mechanisms of structural components of aluminium alloy, Chen et al. (2017). In addition, even the small amounts of elements (Fe, Mn, Mg, Cu, Cr, etc.) are causing the formation of new intermetallic components, thus the exact control of secondary aluminium alloys is necessary, Kobayashi (2000). The main objective of this study was to analyse the microstructural components morphology effect on the fracture behaviour of the A226 cast alloy, since this experimental material is used especially for casting automotive parts, due to its excellent castability, good mechanical properties and cost-effectiveness, Matvija et al. (2012); Sanna et al. (2013) ; Uhríčik et al. (2012). A commercial secondary A226 was investigated in this study. The experimental aluminium alloys (from series Al Si-Cu) are used for cooling fans, crank cases, high speed rotating parts, structural aerospace components, air compressor pistons, fuel pumps, compressor cases, timing gears, rocker arms, machine parts etc. , Drozdov (2007); Kuchariková et al. (2016a). The effect of the microstructure on properties of such products is significant. Alloy was melted in an electric-induction furnace. The molten metal was not modified or grain refined. The testing samples were made from castings by the turning and milling operations, with dimensions corresponding to the standards (STN EN ISO 6892 and STN EN ISO 148-1) for mechanical tests. The chemical composition of experimental alloys was obtained by the arc spark spectroscopy: 9.4 Si, 2.4 Cu, 0.9 Fe, 0.24 Mn, 1.0 Zn, 0.28 Mg, 0.05 Ni, 0.09 Pb, 0.04 Ti, 0.03 Sn, 0.04 Cr and balance of Al (wt. %); thus this is a secondary aluminium alloy, due to the Fe content. The experimental material was heat treated with selected parameters - solution treatment at temperature 515 °C; water quenching at 60 °C and artificial ageing at 170 °C with holding time of 16 hours. After the heat treatment (T6) the samples were subjected to a mechanical test. The absorbed energy (E) was obtained by the impact bending test with the Charpy hammer and the ultimate tensile strength (UTS) by using the shredder machine ZDM 30. Hardness measurement was performed using the Brinell hardness tester: load 62.5 kp (cca 613 N), 2.5 mm diameter ball and a dwell time of 15 s. The values were averaged 2. Experimental procedure