43 KB367 KB41 KB200020242001Anžel, IvanKrižman, AlojzLojen, Gorazdštevilka:1/2letnik:359 stranistr. 37-45ISSN:1580-2949COBISSID:6206486URN:URN:NBN:SI:doc-76O3SL9UslInštitut za kovinske materiale in tehnologijeMateriali in tehnologijealuminijAluminij MostaraluminumbakerkompozitimikrostrukturaohlajanjesilicijstrjevanjeVpliv pogojev strjevanja na mikrostrukturo zlitin in kompozitov s sestavo AlSi17Cu5| Influence of solidification conditions on the microstructure of Al 17wt.%Si 5wt.%Cu alloys and composites|The microstuctures of as-cast alloys depend not only on their chemical composition, they are also strongly affected by process parameters that determine the solidification conditions. The most important of these are the cooling rate and the melt motion during solidification. Traditional csting methods only allow for small variations in the cooling rate, which is more or less determined by the choice of casting method (sand casting, gravity casting in permament moulds, pressure casting). Motion during the solidification is limited to the circulation caused by pouring the melt into the mould. In most cases it is of short duration and too weak to affect the microstructure significantly. The majority of techniques for producing materials with a non-dendritic microstructure (required for thixo casting, thixo forging...) are based on intensive circulation (stirring) during solidification. These techniques afford control of two important production parameters: coolin rate and stirring speed. Nevettheless, the crystallization sequence and the phases present in the materials are still determined by alloy phase diagrams and chemical composition. The chosen cooling rate and stirring speed result in similar nucleation and growth conditions for all phases crystallizing in the stirred melt. Totally different nucleation and growth conditions for differentphases can only br assured if the material is made as a composite. By the "synthesis of semi-solid mixtures" it is possible to manufacture materials containing several primary phases of the corresponding phase diagram. In addition, this production technique enables the individual control of particle size and morphology for each primary phase in the composite. In this paper, microstructures of several Al 17wt.%Si 5 wt.%Cu materials are discussed: three samples were solidified under different coolingrates without forced convection, one was stirred in the semi solid state and two are composites made by the "synthesis of semi-solid mixtures"Mikrostrukture zlitin v litem stanju so, razen od kemijske sestave, odvisne od procesnih parametrov, ki opredeljujejo razmere pri strjevanju. Najvplivnejša sta hitrost ohlajanja in gibanje taline med strjevanjem. Klasični postopki litja dopuščajo le relativno majhen vpliv na hitrost ohlajanja, saj je le-ta okvirno določena že z izbiro postopka (litje v pesek, litje v kokile, tlačno litje ...). Gibanje taline je omejeno na vrtinčenje, ki je posledica ulivanja v formo. V večini primerov je kratkotrajno in prešibko, da bi imelo večji vpliv na mikrostrukturo. Večina postopkov priprave materialov za predelavo v delno staljenem stanju temelji na intenzivnem gibanju taline med strjevanjem, ki omogoča ravoj nedendritne, globulitne morfologije primarnih trdnih faz. Pri teh postopkih je mogoče variirati dva procesna parametra: hitrost ohlajanja in hitrost mešanja. Kljub temu so faze v materialu in zaporedje njihove kristalizacije še vedno skladne s faznim diagramom in s sestavo zlitine. Izbrani hitrosti ohlajanja in mešanja opredeljujeta podobne pogoje nukleacije in rasti za vse faze, ki kristalizirajo iz taline med mešanjem. Bistvenio različne pogoje za nukleacujo in rast delcev posameznih faz v materialih je mogoče izbirati le, če material izdelamo kot kompozit. S postopkom sinteze delno staljenih mešanic je mogoče izdelati materiale, ki vsebujejo več primarnih faz, pri čemer lahko delcem vsake od teh faz predpišemo drugačno obliko in velikost. V tem prispevku obravnavamo mikrostrukture različnih materialov s povprečno kemijsko sestavo AlSi17Cu5: mikrostrukture različno hitro (brez mešanja) strjenih zlitin, zlitine, strjene med mešanjem, in kompozitov, izdelanih s sintezo delno staljenih mešanicTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije