Al-alloys are preferred in the automotive industry because of theirs lightweight. European Union has on the present big interest of share recycling aluminium, and so increase interest about recycled (secondary) aluminium alloys and castings from them. Recycled aluminium alloys are made out of aluminium scrap and workable aluminium garbage by recycling. Due to the increasing production of recycled aluminium cast alloys is necessary their strict metallurgical control. The mechanical properties and the microstructure are dependent on the composition, melt treatment conditions, solidification rate, casting process and the applied thermal treatment. The mechanical properties depend, besides the morphologies, type and distribution of Si, Cu, Mg and Fe-phases, on the grain size, DAS, porosity distribution or profile. Therefore, study the microstructure of Al alloys is very important. Analysis of microstructure in the AlSi9Cu3 alloy was performed on the SEM. For study and identification of intermetallic phases' was utilized standard (Dix-Keller, 0.5% HF) and deep etching. Deep etching consists of dissolving the alphamatrix in the reagent (30 s in HCl) in order to reveal the three-dimensional morphology of the silicon particles and intermetallic phases. For elemental composition of the specimen were used x-rays analysis (line, point and surface -mapping). Finally the fracture surfaces of Al-Si alloy after impact test in the as-cast state were observed.
The contribution describes influence of the age-hardening consist of solution treatment at 515 °C with holding time 4 hours, water quenching at 40 °C and artificial aging at different temperature 150 °C, 170 °C and 190 °C with different holding time 2, 4, 8, 16 and 32 hours on mechanical properties (tensile strength and Brinell hardness) and changes in morphology of eutectic Si, Fe-rich and Cu-rich intermetallic phases in secondary (recycled) AlSi9Cu3 cast alloy. A combination of different analytical techniques (light microscopy upon black-white and colour etching, scanning electron microscopy (SEM) upon deep etching and energy dispersive X-ray analysis (EDX)) were therefore been used for the identification of the various phases. Quantitative study of changes in morphology of eutectic Si, Cu-rich and Fe-rich phases was carried out using Image Analyzer software NIS-Elements. Mechanical properties were measured in line with EN ISO. Age-hardening led to changes in microstructure include the spheroidization and coarsening of eutectic silicon, gradual disintegration, shortening and thinning of Fe- rich intermetallic phases, the dissolution of precipitates and the precipitation of finer hardening phase (Al2Cu) further increase in the hardness and tensile strength in the alloy.
Secondary aluminium alloys are made out of aluminium scrap and aluminium-processable waste by recycling. These alloys contain different alloying elements such as Al, Cu, Fe, Si and Mg that form intermetallic phases in aluminium matrix and influence on the microstructure, basic mechanical properties and microhardness evolution in aluminium cast alloy. As experimental material was used secondary aluminium cast alloy AlSi9Cu3. Material was subjected to heat treatment (age-hardening) consisting of a solution treatment at temperature 515 °C with holding time 4 hours, than water quenching at 40 °C and artificial aging by different temperature 130 °C, 150 °C and 170 °C with different holding time (2, 4, 8, 16 and 32 hours). The age-hardening led to changes in the morphology of structural components, but also leads to precipitation of finer hardening phases in the material substructure. As optimal age-hardening mode for secondary aluminium cast alloy AlSi9Cu3 was determined mode consisting of solution treatment at temperature 515 °C with holding time 4 hours and artificial aging at temperature 170 °C with holding time 16 hours. After this heat treatment cast alloy shows the best changes in microstructure and mechanical properties. These changes are comparable with changes by primary AlSi9Cu3 cast alloy.
Molten aluminium alloy is so active that it an easily chemically react with O2and H2O to form Al2O3 inclusions and H during melting practice. However, some other inclusions form by process. Under turbulent flow conditions, the inclusions are distributed unevenly in molten aluminium alloy. They may associate with crack or by the location of crack initiation in solidified casting. Castings containing these inclusions will probably exhibit poor ductility or toughness. Therefore, the purification of the molten aluminium alloy is one of the most important processes for improving the quality of Al-products. The inclusions in molten secondary AlSi7Mg0.3 cast alloy (without refining or modification; grain refined with 55 ppm AlTi5B1 and modified with 20, 40 and 60 ppm AlSr10) were removed using depth filtration by ceramic foam and pressed filter. The results showed that the mechanical properties through filtration changes. Ductility and UTS of the filtered tensile specimens increases. The better mechanical properties were measured by the using of pressed ceramic filter. Highest UTS and ductility was observed for samples modified with 40 ppm of Sr. Filtration with ceramic filters have very significant influence on the porosity decreasing; in the process the better effect has a pressed filter. In samples modified with 60 ppm of Sr were observed effect of over modification (mechanical properties decreased; porosity increased).
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