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AA2024 ALÜMİNYUM ALAŞIMININ TİKSOTROPİK YAPISI ÜZERİNE SIMA YÖNTEMİNDEKİ DEFORMASYON ORANININ ETKİSİ

EFFECT OF PREDEFORMATION RATE IN SIMA PROCESS ON THIXOTROPIC STRUCTURE OF AA2024 ALUMINIUM ALLOY

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Abstract (2. Language): 
In this study, thixotropic microstructure produced in a wrought AA2024 alloy for the semi-solid forming was investigated by strain induced melt activated (SIMA) method. For this purpose, AA2024 alloy as extruded state were subjected to cold deformation at different rates, following heated to a semi-solid region, and cooled in water at room temperature. Microstructure analysis was achieved by metallographic and quantitative methods. Experimental results showed that spherical shaped thixotropic microstructures which required for semi-solid forming can be produced in AA2024 Al alloy by SIMA process. With increasing cold deformation rate, the shape factor increases while the grain size decreased. For the production of thixotropic structure by SIMA process, cold deformation rate was determined to be necessary at least 20%, and there is no need to isothermal holding at semi-solid temperature for thixotropic structure transformation.
Abstract (Original Language): 
Bu çalışmada, bir dövme alaşım olan AA2024 alaşımında gerinimin neden olduğu sıvı aktivasyonu (strain induced melt activated-SIMA) yöntemi ile yarı-katı şekillendirme için gerekli tiksotropik mikroyapı üretimi araştırılmıştır. Bu amaçla ekstrüze halde AA2024 alaşımı değişik oranlarda soğuk deformasyona tabi tutulmuş ve takiben yarı-katı bölgeye ısıtılarak oda sıcaklığına sahip suda soğutulmuştur. Mikroyapı analizleri metalografik inceleme ve nicel ölçüm yöntemleri ile yapılmıştır. Deneysel sonuçlar, SIMA yöntemiyle AA2024 alaşımında, yarı katı şekillendirme için gerekli olan küresel şekilli tiksotropik mikroyapıların üretilebileceğini göstermiştir. Artan soğuk deformasyon oranı ile şekil faktörü artarken tane boyutu azalmıştır. SIMA yöntemi ile tiksotropik yapı üretimi için en az %20 soğuk deformasyonun gerekli olduğu belirlenmiş ve tiksotropik yapı dönüşümü için yarı-katı sıcaklıkta izotermal bekletmeye gerek olmadığı tespit edilmiştir.
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