Effect of Cryogenic and Natural Aging Treatment Applied to 7075 Al Alloy on Avrami Parameter

Abstract

In this study, after solution heat treatment of 7075 Al alloy, cryogenic treatment was applied at -40 °C for 2 hours and aging heat treatment was performed at room temperature for 10 and 100 days. Other specimens were naturally aged for 10 and 100 days without cryogenic treatment. Each specimen was analyzed by differential scanning calorimetry (DSC) after natural aging. As a result of the analysis, the transformation curves of the metastable η′ phase (MgZn2), known as the main strength phase, were found. Avrami parameters (n) were calculated with Johnson-Mehl-Avrami (JMA) and Ozawa equations. With the calculations, the avram parameter to be obtained at the end of the transformation phase and the growth and nucleation rates were investigated. The results showed that the naturally aged specimen for 10 days after cryogenic treatment grew in two dimensions and had volumetric nucleation. It was found that only naturally aged specimen and naturally aged specimens for 100 days after cryogenic treatment grew to one size and had superficial nucleation.

Keywords

• Natural Aging
• Al 7075
• cryogenic

7075 Al Alaşımına Uygulanan Kriyojenik ve Doğal Yaşlandırma İşleminin Avrami Parametresine Etkisi

Öz

Bu çalışmada 7075 Al alaşımı çözeltiye alma ısıl işleminden sonra -40 °C de 2 saat kriyojenik işlem uygulanıp oda sıcaklığında 10 ve 100 gün yaşlandırma ısıl işlemi yapılmıştır. Diğer numuneler ise kriyojenik işlem uygulamadan doğal yaşlanma işlemi 10 ve 100 gün yapılmıştır. Her numune doğal yaşlanma işleminden sonra differential scanning calorimetry (DSC) ile analiz edilmiştir. Analizler sonucu ana mukavemetlenme fazı olarak bilinen yarı kararlı η′ fazının (MgZn2) dönüşüm eğrileri bulunmuştur. Johnson-Mehl-Avrami (JMA) ve Ozawa eşitliği ile avrami parametreleri (n) hesaplanmıştır. Hesaplamalar sonuncunda elde edilecek olan avrami parametresi ile dönüşümün gerçekleştiği fazın kaç boyutta büyüme ve çekirdeklenme gösterdiği araştırılmıştır. Sonuç olarak kriyojenik işlem sonrası 10 gün doğal yaşlandırma yapılan numunenin iki boyutta büyüdüğünü ve hacimsel çekirdeklendiğini göstermiştir. Sadece doğal yaşlanan numunelerin ve kriyojenik işlem sonrası 100 gün doğal yaşlanma yapılan numunenin ise tek boyutta büyüdüğü ve yüzeysel çekirdeklendiği bulunmuştur.

Anahtar Kelimeler

• Doğal yaşlandırma

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