Bakır ve Magnezyum Katkılarının Al-17Si Alaşımının Yapısal, Mekanik ve Tribolojik Özelliklerine Etkisi

İkili Al-17Si, üçlü Al-17Si-4Cu ve dörtlü Al-17Si-4Cu-0,6Mg alaşımları kokil kalıba döküm yöntemiyle üretildi. Üretilen alaşımların kimyasal bileşimleri spark optik emisyon spektrometresi (Spark OES) yöntemi ile belirlenerek doğrulandı. İçyapı incelemeleri standart metalografik yöntemlerle hazırlanan numuneler üzerinde ışık ve taramalı elektron mikroskobu (SEM) ile gerçekleştirildi. Alaşımların sertliği Brinell sertlik ölçme yöntemiyle, akma ve çekme dayanımı ile kopma uzaması değerleri ise üniversal bir test makinesinde yapılan çekme deneyleri ile belirlendi. Çekme deneylerine tabi tutulan numunelerin yüzeyleri ve yüzey altları SEM’de incelenerek görüntülendi. Alaşımların tribolojik özellikleri bilye disk esaslı bir deney düzeneği yardımıyla belirlendi. Al-17Si alaşımının içyapısının alüminyumca zengin α, ötektik Al-Si, primer silisyum ve β fazlarından, üçlü Al-17Si-4Cu alaşımının Al-17Si alaşımındaki fazların yanı sıra bakırca zengin θ (CuAl2) fazını da içerdiği görüldü. Dörtlü Al-17Si-4Cu-0,6Mg alaşımında ise üçlü Al-17Si-4Cu alaşımındaki fazlara ilave olarak Mg2Si fazının oluştuğu ve ayrıca ikili ve üçlü alaşımda görülen β fazının dörtlü alaşımda π fazına dönüştüğü belirlendi. Bakır ve magnezyum katkılarının incelenen alaşımların sertlik, akma ve çekme dayanımı ile birlikte aşınma direncini arttırdığı, kopma uzaması değerlerini ise düşürdüğü gözlendi. Mekanik ve tribolojik deneylerden elde edilen sonuçlar alaşımların yapısal özelliklerine dayandırılarak irdelendi.

Anahtar Kelimeler:

Al-17Si esaslı alaşımlar, İçyapı, Mekanik özellikler, Aşınma, Kırılma

Effect of Copper and Magnesium Additions on the Structural, Mechanical and Tribological Properties of the Al-17Si Alloy

Binary Al-17Si, ternary Al-17Si-4Cu and quaternary Al-17Si-4Cu-0.6Mg alloys were produced by permanent mold casting method. Chemical composition of the produced alloys was confirmed by spark optical emission spectrometry (Spark OES) method. Structural examinations of the alloys were carried out with optical and scanning electron microscopy (SEM) on the samples prepared by standard metallographic methods. The hardness of the alloys was determined by the Brinell hardness measurement method. The hardness of the alloys was determined by the Brinell hardness measurement method. The values of the elongation to fracture, yield and tensile strength of the alloys produced were determined by tensile tests performed with a universal testing machine. The fracture surfaces and the sub-surfaces of the tensile test samples were examined by SEM. Tribological characteristics of the alloys were investigated by a ball-on-disc type friction-wear test machine. It was observed that microstructure of the Al-17Si alloy consisted of the phases of aluminum-rich α, eutectic Al-Si, primary silicon and β. Ternary Al-17Si-4Cu alloy showed a microstructure consisting of the phase of θ(CuAl2) in addition to phases observed in the Al-17Si alloy. Al-17Si-4Cu-0,6Mg alloy showed a microstructure consisting of Mg2Si in the addition to the phases observed in the ternary alloy. In addition to this the β phase observed in the ternary alloy turned into π phase in the quaternary alloy. Copper and magnesium additions resulted in an increase in the wear resistance, hardness, yield and tensile strength of the alloys tested, but a decrease in the elongation to fracture. The results obtained from mechanical and tribological tests were discussed on the basis of structural changes observed in the alloys due to copper and magnesium additions.

Keywords:

Al-17Si based alloys, Microstructure, Mechanical properties, Wear, Fracture,

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