Influence of the return material on the AlSi9Cu3(Fe) alloy properties

Standardna AlSi9Cu3(Fe)aluminijska legura najčešće se koristi za proizvodnju odljevaka tehnologijom visokotlačnog lijevanja, a primjenjuje se u automobilskoj industriji za izradu nosača motora, kućišta mjenjača, kućišta generatora, kućišta turbopunjača itd. Prednosti AlSi9Cu3(Fe) legure su relativno visoka mehanička svojstva, čvrstoća i tvrdoća uz nešto nižu otpornost na istezanje i koroziju. Na razvoj mikrostrukture i mehanička svojstva legure pored kemijskog sastava, tehnološke obrade taline, procesa lijevanja te mogućnosti toplinske obrade, značajno utječe sastav uložnog materijala. Porast udjela povratnog uložnog materijala utjecat će na razvoj mikrostrukture tijekom skrućivanja te uzrokovati smanjenje mehaničkih svojstava konačnog proizvoda. Cilj ovog rada je usporediti mehanička svojstva uzoraka AlSi9Cu3(Fe) legure neposredno nakon te 4 i 80 tjedana nakon lijevanja proizvedenih uz primjenu 100% povratnog uložnog materijala. Metalografska ispitivanja pokazala su da mikrostruktura ne odstupa značajno od uobičajene prakse primjenom 50% i 100% povratnog uložnog materijala. Uočeni su sljedeći mikrostrukturni konstituenti: dendritna mreža primarnog αAl, eutektik (αAl + βSi), primarni βSi, β – Al5FeSi u obliku iglica, α – Al15(Mn,Fe)3Si2 u poligonalnom obliku i obliku kineskog pisma, te Al2Cu nepravilnog oblika izlučen u interdendritnom području. Mehanička ispitivanja pokazala su odstupanje granice razvlačenja od zahtijevanih vrijednosti odmah i 4 tjedna nakon lijevanja unatoč istim mikrostrukturnim konstituentima. Nakon 80 tjedana uočava se učinak prirodnog starenja koje doprinosi porastu granice razvlačenja te slijedom navedenog zadovoljavanje zahtjeva norme EN 1706.The standard AlSi9Cu3(Fe) aluminium alloy is mostly used for the production of the castings with the use of high-pressure casting. It is used in the car industry for manufacturing engine block carriers, gearbox housings, generator housings, turbocharger housings, etc.The AlSi9Cu3(Fe) alloys are characterized by relatively high mechanical properties, strength, and hardness, with slightly lower resistance to strain and corrosion. Besides chemical composition, melt treatment and the possibility of various heat treatments, the microstructure and mechanical properties of the alloy are significantly influenced by the composition of the return material.The development of microstructure is influenced by the increase of the returnable material in the melt during solidification and it can decrease mechanical properties of the final product. The aim of this research is to compare the mechanical properties is the comparison of the mechanical properties of the AlSi9Cu3(Fe) alloy immediately after,4 and 80 weeks after casting obtained with the application of 100 % returnable material. The metallographic testing showed that the microstructure of such alloy does not deviate significantly from usual practice obtained by using 50% or 80% of returnable material. Following microstructural constituents wereidentified: dendritic network of primary αAl, eutectic (αAl + βSi),primary βSi,needle-shaped β – Al5FeSi, α – Al15(Mn,Fe)3Si2 in polygonal shape and in the shape of Chinese scriptalong with irregularly shaped Al2Cu precipitated the interdendriticareas. Mechanical testing showed deviation of the yield strength from required values immediately after casting and 4 weeks after casting despite the same microstructure constituents. After 80 weeks, the effect of natural ageing led to the increase in yield strength and achievement of satisfactory mechanical properties in accordance with EN 1706 standard