2011

LJEVARSTVO BR. 1/2011

Prethodna priopćenja

J. Groš, M. Ferenc i I. Budić

Ispitivanje livljivosti pri lijevanju u pune jednokratne kalupe

            SAŽETAK

             Pri lijevanju u pune jednokratne kalupe često se primjenjuju pjenasti polistirenski modeli koji se pri ulijevanju taline rasplinjuju. Modeli su najčešće jednodijelni, a proces lijevanja se naziva postupkom ''izgubljenog modela'' jer se model pri ulijevanju taline rasplinjuje (nestaje), a njegovo mjesto zauzima talina. Prilikom ulijevanja taline može  rasplinjavanje modela biti nepotpuno, pa dolazi do smanjenja livljivosti i pojave pogrješaka na odljevcima. Da bi se izbjegle ove pojave potrebno je detaljnije istraživanje livljivosti, uzimajući u obzir različite gustoće polistirena.

            Ključneriječi: livljivost, polistiren, lijevanjeupunejednokratnekalupe

Testing of Castability during Pouring into Full One Part Moulds

            ABSTRACT

            Expandable polystyrene (EPS) or lost foam patterns, which evaporate during pouring into one part moulds are frequently used. The used moulds are regularly one part moulds, and the casting process is called “lost foam” process, because moulds evaporate (vanish) during pouring of the melt and their place is taken by the melt itself.

During pouring of the melt incomplete evaporation of the mould may occur, accompanied by reduced castability and defects on casts. To avoid such occurrences, need for detailed research of castability, taking into account different densities of polystyrene, has been imposed.

            Key words: castability, polystyrene, pouring into full one part moulds

J. Malina, N. Dolić i A. Markotić

Korozijska otpornost aluminijskih slitina EN AW-5083 i

EN AC-44200 u lijevanom stanju

Corrosion Resistance of Aluminum Alloys EN AW-5083 and EN AC-44200 in As-Cast Conditions

SAŽETAK

Aluminij je metal koji ima veliki značaj u suvremenoj tehnici i može se s pravom nazvati materijalom budućnosti ako se ima u vidu njegova primjena posljednjih godina. Raširena uporaba aluminija i njegovih slitina potaknuta je izvrsnim mehaničkim svojstvima, tj. velikom čvrstoćom, manjom masom u odnosu na iste odljevke od drugih materijala, a odlikuje ih također dobra livljivost, zavarljivost, otpornost prema koroziji, otpornost prema trošenju i strojna obradivost. Zbog svega toga Al slitine sve se više primjenjuju u mnogim industrijskim granama kao npr. u proizvodnji transportnih vozila (automobilska, zrakoplovna industrija, brodogradnja, industrija željezničkih vozila), u građevinarstvu, strojogradnji i drugdje.

            Stoga su u ovom radu proučavana korozijska svojstva dviju aluminijskih slitina u lijevanom stanju: gnječive Al-Mg slitine s povišenim udjelom magnezija (EN AW-5083) i ljevačke Al-Si slitine eutektičkog sastava (EN AC-44200). Primjenom elektrokemijskih mjernih tehnika (potenciodinamička polarizacijska mjerenja i ciklički voltamogrami) određene su elektrokemijske značajke lijevanih slitina, sa ciljem da se odredi njihova sklonost općoj i lokalnoj koroziji u neutralnom kloridnom mediju (0,01 M NaCl).

Rezultati su pokazali da obje ispitivane slitine pokazuju sklonost pasivaciji. Međutim, Al-Si slitina pokazuje više vrijednosti potencijala jamičaste korozije tj. manju sklonost lokalnoj koroziji od Al-Mg slitine. Isti zaključak vrijedi i za otpornost prema općoj koroziji: Al-Si slitina korodira manjom brzinom, što se može pripisati većoj stabilnosti barijernog oksidnog sloja na njenoj površini.

            Ključne riječi: aluminijske slitine, EN AW-5083, EN AC-44200, lijevano stanje, kloridni medij, korozija

           ABSTRACT

Aluminum is a metal that has a great importance in modern technology and can be rightly called a material of the future, if we have in mind its use in recent years. Widespread use of aluminum and its alloys is characterized by the excellent mechanical properties, i.e. high strength, lower mass compared to the casting of other materials, as well as by good castability, weldability, corrosion resistance, resistance to wear and mechanical workability. Because of this, Al-alloys have found its application in many industrial branches such as production of transport vehicles (automotive, airplane, shipbuilding and industry railway vehicles), civil engineering, production of machinery, etc.

Therefore, in this work the corrosion properties of two aluminum alloys were studied: wrought Al-Mg alloy with high Mg content (EN AW-5083) and eutectic Al-Si alloy (EN AC-44200), the both in as-cast condition. Using electrochemical measurement techniques (potenciodynamic polarization measurements and cyclic voltamograms) the electrochemical characteristics of alloys were determined with the aim to evaluate their tendency to general and local corrosion in neutral chloride media (0.01 M NaCl).

The results have shown that both studied alloys are prone to passivation. However, Al-Si alloy has more noble value of pitting potential, i.e. less tendency to local corrosion than Al-Mg alloy. The same conclusion is valid for the resistance of Al-Si alloy to general corrosion: Al-Si alloy is characterized with decreased corrosion rate due to higher stability of oxide layer on its surface.

            Key words: aluminum alloys, EN AW-5083, EN AC-44200, as–cast condition, chloride medium, corrosion

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