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1.
Challenges and advantages of recycling wrought aluminium alloys from lower grades of metallurgically clean scrap
Varužan Kevorkijan, 2013, review article

Abstract: In the recycling of wrought aluminium alloys from lower grades of scrap (metallurgically clean but highly contaminated with non-metallic impurities) the following two tasks were identified as the most demanding: (i) achieving the required final chemical composition of an alloy with a minimal addition of primary aluminium and alloying elements; and (ii) keeping the level of impurities (inclusions, hydrogen, trace elements and alkali metals) in the molten metal below the critical level. Because of the lack of chemically based refining processes for reducing the concentration of alloying and trace elements in the molten aluminium, once the concentrations of these constituents in the melt exceed the corresponding concentration limits, the only practical solution for their reduction would be an appropriate dilution with primary metal. To avoid such a costly correction, carefully predicting and ensuring the chemical composition of the batch in the pre-melting stage of casting should be applied. Fortunately, some of the impurities, like hydrogen and alkali metals, as well as various (mostly exogeneous) inclusions, could be successfully reduced by employing existing refining procedures. In this work, (i) the state-of-the-art technologies, including some emerging technical topics such as the evolution of wrought alloys toward scrap-intensive compositions, monitoring of the content of organics in the incoming scrap and the quality of molten metal achieved by different smelting and refining technologies, and (ii) the relevant economic advantages of the recycling of wrought aluminium alloys from the lower grades of scrap are reported. By analyzing the market prices of various grades of scrap and the total cost of their recycling, the cost of aluminium ingots made from recycled aluminium was modelled as a function of aluminium and the alloying-element content in the incoming scrap. Furthermore, scrap mixtures for producing aluminium wrought alloys of standard quality from lower grades of scrap and with a significant new added value were illustrated.
Keywords: wrought aluminium alloys, recycling, low grades of aluminium scrap, quality of recycled metal, economic benefits
Published in DKUM: 21.12.2015; Views: 1608; Downloads: 44
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2.
The introduction of fine SiC particles into a molten Al alloy matrix : application to composite material casting
Varužan Kevorkijan, Borivoj Šuštaršič, 1995, published scientific conference contribution

Abstract: The immersion of fine SiC particulates into a Al is one of the major factors hampering the commercial development of particle reinforced composites prepared by liquid metallurgy techniques. Smaller particles are generally more difficult to wet and disperse than larger particles because of their inherently greater surface area. On the other hand, smaller particles generally give MMCs with superior mechanical properties. The challenge is to control the reaction between the matrix and reinforcement particles to achieveimproved wetting so that good distribution and interfacial bonding are obtained. This paper will review the actual technological challenge of fine particulate reinforced MMC fabrication, and will describe the most promissing new processes.
Keywords: kompozitni materiali, livarstvo, omakanje, keramični delci
Published in DKUM: 10.07.2015; Views: 1062; Downloads: 38
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3.
Carbothermal synthesis of submicrometer [beta]-SiC powder using double precursor reaction mixture
Varužan Kevorkijan, 1995, original scientific article

Abstract: Carbothermal synthesis of submicrometer beta-SiC powder using double precursor reaction mixture
Published in DKUM: 10.07.2015; Views: 987; Downloads: 32
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4.
Experimental investigation of the stability of particulate dispersoid suspensions in aluminium and magnesium melts
Varužan Kevorkijan, 2000, original scientific article

Abstract: The rejection of Si3N4,Mg3N2, AlN and Si particles from different slurries consisting of molten aluminum and magnesium alloy with 10% of silicon or pure molten metals was experimentally investigated by measuring changes in the electrical resistance of the slurries before and after rejection occurred. In stirring experiments, only individual powder fractions which passed through a 45 µm sieve screen and remained on a 30 µm screenwere applied. The experiments showed that the rejection of Si3N4 particles from Al-10%Si and Mg-10%Si melts occurs when more than 17-18 vol.% of the ceramic phase is dispersed into the melt, while in pure Al and Mg molten metals spontaneous rejection occurs at 7-8 vol.% of the introduced ceramic phase. A similar tendency of rejection (at 16-18 vol.% of particulate in slurry) was also observed during the introduction of silicon particles into Al-10%Si and Mg-10%Si melts.
Keywords: metal matrix composites, particle reinforcement, interface, chemically activated wetting
Published in DKUM: 01.06.2012; Views: 1793; Downloads: 85
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5.
Ekonomski učinki predelave stranskih produktov recikliranja odpadnega aluminija in aluminijeve žlindre v tržno zanimive in okolju neškodljive izdelke
Varužan Kevorkijan, 2001, professional article

Abstract: V delu obravnavamo postopke recikliranja aluminijevih zlitin iz odpadnega aluminija in aluminijeve žlindre s pretaljevanjem v rotacijski peči konvertorskega tipa, ogrevani z gorilnikom na zemeljski plin in kisik. Opisani so trije postopki pretaljevanja odpadnega materiala: klasični, "mokri" postopek z dodatkom soli v razmerju 1:1 glede na vsebnost nealuminijskih sestavin v odpadnem materialu, "suhi" postopek z dodatkom soli 0,6:1 glede na nealuminijske sestavine v odpadnem materialu in postopek pretaljevanja brez dodatka soli, ki se večinoma uporablja le za pretaljevanje aluminijeve žlindre. Osnovni problem, ki se pojavlja pri vseh treh postopkih recikliranja aluminijevih zlitin iz odpadnega aluminija in aluminijeve žlindre je predelava stranskih produktov pretaljevanja odpadnega materiala v koristne in okolju neškodljive izdelke oz. surovine za nadaljnjo uporabo. Pri "mokrem" in "suhem" postopku gre za predelavo t.i. "slanega kolača", pripostopku pretaljevanja brez dodatka solipa za predelavo "nekovinskega ostanka". Opisani so in ekonomsko ovrednoteni različni postopki recikliranja soli iz "slanega kolača" in predstavljeni možni postopki nadaljnje predelave "nekovinskega ostanka".
Keywords: aluminijeve zlitine, recikliranje, odpadni aluminij, aluminijeva žlindra, pretaljevanje v rotacijski peči, stranski produkti, slani kolač, nekovinski ostanek
Published in DKUM: 01.06.2012; Views: 2511; Downloads: 146
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6.
Production technology and use of aluminium drop forging components
Varužan Kevorkijan, 2001, professional article

Abstract: In this report the production and use of forged aluminium parts are described and the automobile and other principal markets for forged aluminium componnts are outlined.
Keywords: drop forging, lightening, aluminium alloys, forged automobile components
Published in DKUM: 01.06.2012; Views: 1727; Downloads: 105
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7.
Odkovki iz gnetnih magnezijevih zlitin (GMZ) in Mg/SiC kompozitov za novo generacijo osebnih avtomobilov : (predlog evropskega projekta)
Varužan Kevorkijan, 2002, review article

Abstract: V okviru predloženega evropskega projekta želimo v polindustrijskem merilu raziskati tehnološke možnosti in ekonomsko upravičenost izdelave lahkih, vroče utopno kovanih avtomobilskih delov iz: a) komercialnih, gnetnih magnezijevih zlitin b) Mg-kompozitov, diskontinuirano ojačanih s keramičnimi delci ter c) Mg-Li-zlitin s kubično centrirarno kristalno strukturo, od katerih se pričakuje večja preoblikovalnost. Načrtujemo, da bomo najprej določili novo obliko in dimenzije izbrane avtomobilske ojnice, ki jo domači proizvajalci komercialno izdelujejo iz Al-zlitine 2014. S tem bo omogočeno ustrezno funkcionalno nadomeščanje aluminijeve zlitine 2014 z različnimi GMZ s heksagonalno kristalno zgradbo (AZ80A, ZK60A, WE43) in Mg-kompozitom, ojačanim z delci SiC (MELRAM) ter vsaj z eno Mg-Li-zlitino, ki ima kubično centrirano kristalno strukturo. Z vročim utopnim kovanjem bomo v (pol)industrijskem merilu iz vsake uporabljene Mg-zlitine oz. kompozita (MELRAM) izdelali 30-50 ojnic, ki jih bomo obrezali in termično obdelali. Določili bomo mehanske lastnosti izdelanih prototipnih ojnic in na podlagi dobljenih rezultatov preverjali ekvivalentnost njihovih mehanskih lastnosti z ojnicami, izdelanimi iz Al-zlitne 2014. Na osnovi eksperimentalnih ugotovitev bomo po potrebi spreminjali in dopolnjevali prej določeno obliko in geometrijo avtomobilskih ojnic, vse dokler ne bodo njihove funkcionalne lastnosti v praksi enake lastnostim ojnic, izdelanih iz zlitine 2014. Ugotavljali bomo tudi morebitne razlike v preoblikovalnosti med Mg-zlitinami s heksagonalno in kubično centrirano kristalno zgradbo. V nadaljevanju bomo eksperimentalno določali prihranek mase, ki ga povzroča nadomeščanje aluminijeve zlitine 2014 z omenjenimi magnezijevimi zlitinami in kompozitom-Mg/SiC (MELRAM). Ugotovljen prihranek mase bomo tržno ovrednotili in hkrati raziskali, ali bi lahko z obstoječo tehnologijo vročega utopnega kovanja ponudili trgu zadosti konkurenčne odkovke iz Mg-zlitin in Mg/SiC-kompozita (MELRAM). Sodeč po svojih mehanskih lastnostih, ki so primerljive z nekaterimi Al-zlitinami, bi ti lahko v bližnji prihodnosti omogočili nadomeščanje jeklenih in v določenih primerih aluminijastih avtomobilskih delov z lažjimi, izdelanimi iz materialov na osnovi magnezija. Pred tem bi tehnološka in ekonomska analiza morali pokazati, ali bi se in pod kakšnimi pogoji tovrstna zamenjava materialov tržno izplačala. Cilj projekta je ponuditi avtomobilskemu trgu novo generacijo zelo lahkih odkovkov. Ti bodo prispevali k manjši porabi goriva v osebnih avtomobilih in s tem v zvezi k manjšemu onesnaževanju okolja.
Keywords: metalurgija, gnetne magnezijeve zlitine, vroče utopno kovanje, odkovki, osebni avtomobili, avtomobilska industrija, zniževanje teže
Published in DKUM: 01.06.2012; Views: 3919; Downloads: 171
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