Influence of technological procedures on the surface quality of extruded EN AW 6060 alloy profiles

V diplomskem delu je predstavljen postopek tehnoloških ukrepov, ki omogoča odpravo ne zaželenih lis na anodizirani površini iztisnjenih profilov iz aluminijeve zlitine EN AW 6060. V uvodu diplomskega dela spoznamo problem vizualne kvalitete iztisnjenih profilov, s katerim se ukvarjamo. V teoretičnem delu so predstavljeni segmenti, ki jih moramo poznati in razumeti, saj v veliki meri vplivajo na kočno kvaliteto površine iztisnjenih profilov. To so: osnove aluminijevih zlitin, tehnološki postopek litja drogov, proces iztiskavanja in vpliv njegovih parametrov, proces staranja in anodizacija. Pri eksperimentalnem delu je bil cilj ugotoviti, ali se na površini iztisnjenih profilov po anodizaciji pojavljajo lise, če v kemijski sestavi aluminijeve zlitine EN AW 6060 povečamo masni delež železa w(Fe) na zgornjo mejo 0,3 %, ki jo določuje standard. Profile smo iztiskali pri različnih temperaturah predgretja okroglic, z namenom ugotovitve katera kombinacija privede do najlepše površine po anodizaciji. Za najboljše vzorce smo optimizirali umetno staranje in poleg doseganja zahtevanih mehanskih lastnosti ugotavljali tudi njegov vpliv na pojav lis na anodizirani površini. Izvedene so bile analize mikrostrukture, katere smo analizirali in primerjali med vzorci. Ugotovljeno je bilo, da je površina po anodizaciji kvalitetnejša pri zlitini z nižjim deležem železa in višji temperaturi predgretja okroglice. Umetno staranje ima prav tako velik vpliv na prisotnost lis na anodizirani površini, razlog pa tiči v prisotnosti Mg2Si in AlFeSi faz blizu površine, ki zmanjšujejo prevodnost in posledično uničujejo kvaliteto anodizacijskega nanosa.The thesis presents the process of technological measures that make it possible to eliminate unwanted visual lines on the anodized surface of extruded profiles made of aluminum alloy EN AW 6060. In the introduction to the thesis, we learn about the problem of the visual quality of extruded profiles, which we are dealing with. In the theoretical part, the segments that we need to know and understand are presented, as they largely affect the surface quality of the extruded profiles. These are: the basics of aluminum alloys, the technological process of casting billets, the extrusion process and the influence of its parameters, the artificial aging process and anodization. In the experimental work, the aim was to determine whether visual lines appear on the surface of extruded profiles after anodization, if the mass fraction of iron w(Fe) in the chemical composition of aluminum alloy EN AW 6060 is increased to the upper limit of 0.3 %, which is determined by the standard. The profiles were extruded at different preheating temperatures of the billets, with the aim of finding out which combination leads to the most beautiful surface after anodization. Artificial aging was optimized for the best samples and, in addition to achieving the required mechanical properties, we also determined its effect on the appearance of visual lines on the anodized surface. Microstructure analyzes were carried out, which were analyzed and compared between the samples. It was found that the surface after anodization is of better quality with an alloy with a lower proportion of iron and a higher preheating temperature of the billet. Artificial aging also has a great influence on the presence of visual lines on the anodized surface, and the reason lies in the presence of Mg2Si and AlFeSi phases near the surface, which reduce conductivity and consequently destroy the quality of the anodizing coating