Optimization of heat-treatment for A356.0 alloy

Namen magistrskega dela je bil raziskati problematiko premajhnega raztezka in njegovega nihanja pri določenih ulitkih, ki jih izdeluje podjetje Talum, d. d. V ta namen smo podrobneje proučevali dosežene kemijske sestave ulitkov in njihovo toplotno obdelavo. Ulitki so liti po tehnologiji nizkotlačnega litja in toplotno obdelani po režimu toplotne obdelave T6, ki vključuje raztopno žarjenje, gašenje in umetno staranje pri povišani temperaturi. V teoretičnem delu so podane osnovne informacije o livnih aluminijevih zlitinah, podrobneje o skupini 3xx.x, v katero spada tudi obravnavana zlitina, teoretične osnove priprave materiala in nizkotlačnega litja ter toplotne obdelave. V eksperimentalnem delu je predstavljen potek raziskav, ki so bile opravljene v okviru tega magistrskega dela. Za izvedbo raziskav smo uporabili osem ulitkov iz podjetja Talum, d. d. Dva sta ostala v litem stanju, dva smo preiskovali po raztopnem žarjenju, dva po celotni toplotni obdelavi v podjetju Talum, d. d., na dveh pa smo na Naravoslovnotehniški fakulteti izvedli lastno toplotno obdelavo. Iz ulitkov smo izrezali standardne preizkušance za natezni preizkus, s pomočjo svetlobne mikroskopije pregledali mikrostrukturo, izvedli kemijsko analizo s pomočjo energijske disperzijske spektroskopije in pregledali prelome nateznih preizkušancev s pomočjo vrstične elektronske mikroskopije. Po analizi rezultatov smo ugotovili, da nam je z lastno toplotno obdelavo sicer uspelo povišati raztezke, vendar pa sta se preveč zmanjšali natezna trdnost in meja plastičnosti, ki nista dosegali vrednosti, predpisanih s strani kupca. Nadalje smo ugotovili, da pri vseh ulitkih kemijska sestava odstopa od predpisane, kar lahko negativno vpliva na raztezek. Pri analizi prelomov smo ugotovili poroznost v vseh nateznih preizkušancih, kar prav tako negativno vpliva na raztezek.The purpose of the master thesis was to investigate the problem of insufficient elongation and variations thereof at certain castings manufactured by the company Talum, d.d. For this, we further studied the obtained chemical composition of castings and their heat treatment. The pieces are cast by low-pressure casting technology and heat-treated under the regime of heat treatment T6. First they were solution annealed and then quenched in water and artificially aged. The theoretical part provides basic information on the casting of aluminum alloys, details about the group to which it belongs 3xx.x basis for preparing material and low-pressure die casting and heat treatment, with emphasis on the T6. In the experimental part the course of research that have been conducted within the framework of this master\u27s thesis is presented. To carry out the research, we used eight castings of Talum, d.d. Two pieces remained in the as-cast state, two were examined in solution treated state, two after the full heat treatment in the company Talum, d.d., while two were checked after own heat treatment conducted in the Faculty of Natural Sciences. On the pieces we performed tensile tests, examination of the microstructure using light microscopy, chemical analysis using energy dispersive spectroscopy and tensile fractures review using scanning electron microscopy. After analyzing the results, we find that with our own heat treatment we succeeded to increase elongation, but the tensile strength and yield were both reduced, which did not achieve the values prescribed by the buyer. Furthermore, we find that all pieces of the chemical composition deviates from the prescribed, which may adversely affect the elongation. When analyzing the fracture surface, we found a porosity of tensile specimens, which also has a negative effect on elongation