Sezgin YAŞA, Ahmet KABİL, Yahya BAYRAK, Mustafa ÇİĞDEM

Sr ilavesinden sonra bekletme süresinin A356 alaşımının mikroyapısal ve mekanik özelliklerine etkisi

Alüminyumdaki silisyum ötektik fazının küreselleşmesi, döküm için önemli bir parametredir ve malzeme özelliklerini önemli ölçüde etkiler. Sr alüminyumda ötektik modifikasyon için uzun süredir kullanılmaktadır ve bu konuda birçok araştırma yapılmıştır. Bu çalışmada Sr ilavesinden sonra bekletme süresinin alüminyumun mekanik özelliklerine ve ötektik faz modifikasyonuna etkisi incelenmiştir. Modifikasyon için 200 ppm Sr, bekletme süreleri ise 20, 40 ve 80 dk. olarak seçilmiştir. Mekanik özelliklerin tespiti için çekme testi yapılarak çekme dayanımı ve uzama değerleri ölçülmüştür. Ötektik modifikasyonu ölçmek için, ötektik silisyum partiküllerinin boy/en oranları ölçülmüştür. Ek olarak, sıvı metalin Bifilm indeksi vakum altında katılaştırma testi (VAK) ile ölçülmüştür. Bekleme süresindeki artışla birlikte, en boy oranında ve Bifilm indeksinde artış gözlenmiştir. Çekme dayanımı ve uzama değerlerinin ise tutma süresi arttıkça azaldığı gözlenmiştir.

The effect of holding time after Sr addition on microstructural and mechanical properties of A356 alloy

The spheroidization of the silicon eutectic phase in aluminum is animportant parameter for casting and significantly influences thematerial properties. Sr has been used for a long time for eutecticmodification in aluminum and many researches have been made on thissubject. In this study, the effect of holding time after Sr addition on themechanical properties and eutectic phase modification of the aluminumwere investigated. 200 ppm Sr was chosen as the amount of Sr and theholding times were chosen as 20, 40 and 80 minutes. Tensile test wasperformed for the determination of mechanical properties and ultimatetensile strength and percentage of elongation values were measured. Inorder to quantify eutectic modification, the length / width (aspect ratio)ratios of eutectic silicon particles were measured. In addition, BifilmIndex of the molten metal was determined with the reduced pressuretest (RPT). With the increase in the holding time, an increase in theaspect ratio and in the Bifilm Index was measured. It has been observedthat the tensile strength and elongation values have decreased as theholding time has increased.

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