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چكيده انگليسي :

Development of an One Step shape Casting method for Direct Formation of Non Dendritic Microstructure from Liquid State Mehdi Kaskani m kaskani@ma iut ac ir Date of Submission 2012 03 17 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Behzad Niroumand behzn@cc iut ac irAbstractProduction of semisolid metallic components starts with a slurry of suspended non dendritic solidparticles Such slurries are commonly produced by applying shear stress to a solidifying melt or byencouraging copious nucleation during initial stages of solidification As yet all the employedmethods use a two steps processing where in the first step the non dendritic slurry is prepared in acontainer outside the die and then the slurry is cast into the die Furthermore higher viscosity ofsemisolid metallic slurries have practically made their gravity casting impossible and resulted in aneed for some sort of mechanical force to push such viscous slurries into the die cavities Thisnecessitates the use of expensive high strength metallic dies Therefore only mass production ofsemisolid components has been economically justified so far The main objective of this work wasto develop a single step semisolid part production method and investigate the possibility ofachieving non dendritic microstructure in A356 alloy during sand casting without the need for anyexpensive metallic die or any special previous processing on the melt For this purpose in the firststep a sand mould with three different types of running systems was designed and its mold fillingand solidification process were simulated using ProCAST simulation software Second stepinvolved casting of A356 alloy from fully liquid state in the three types of running systems undergravity and centrifugal casting conditions The cast microstructures were then studied In the thirdstep the alloy was centrifuge cast from semisolid state in the three types of running systems andmicrostructure and fluidity length of all the castings as well as hardness porosity content andtensile properties of some of the castings were studied Microstructural investigations in the secondstep showed that non dendritic structures could be produced by using a chill fitted sand core in thesprue of the gating system and reducing the superheat temperature under centrifugal castingcondition Also casting under centrifugal rather than gravity condition and reducing the superheattemperature reduced the grain size Size of the primary particles and primary particle groupings aswell as roundness of the primary particles increased with an increase in the solid fraction androundness of primary particle groupings decreased with an increase in the solid fraction Withchanging the running system design from first to third at a given solid fraction size of primaryparticles decreased and their roundness increased With investigation of fluidity length it is shownfluidity length decreased in three running systems with increasing solid fraction Casting undercentrifugal condition lower superheat temperature and using third running system increased thehardness of the parts cast from fully liquid state With an increase in the solid fraction hardness ofparts cast from semisolid state decreased Mechanical properties of cast parts increased undercentrifugal casting condition and lower superheat temperature Keywords Non dendritic structure Semi solid alloys Gravity casting Centrifugal casting A356alloy

كسكني، مهدي

توسعه يك روش قطعه ريزي تك مرحله اي جهت توليد مستقيم ريز ساختار غير دندريتي از مذاب

آلياژهاي نيمه جامد , ريخته گري ثقلي , ريخته گري گريز از مركز A356