Al – Zn – Mg – Cu Alaşımının Kristalografisine RRA Isıl İşlemi Etkilerinin İncelenmesi

Dayanıklılığın, yani mukavemetin ağırlık oranının birincil gereklilik olduğu yapısal uygulamalarda demir esaslı malzemelerin benzer özelliklere sahip malzemelerle yer değiştirmesi gerekir. Isıl işlem görebilir 7075 alüminyum alaşımı, dayanımının çeliklerinkiyle karşılaştırılabilir olması ve otomobil, uçak endüstrisi ile denizcilik uygulamalarında yaygın olarak kullanılması nedeniyle araştırmacıların ortak ilgi alanına giren alüminyum alaşımlarından biri olarak kabul edilir. Yüksek sertlik ve mukavemetinin yanında hafifliği ile savunma endüstrisinin en önemli alaşımlarından biridir. Bu çalışmada ticari olarak satın alınan T651 ısıl işlemi uygulanmış Al – Zn – Mg– Cu alaşımının yeniden çözeltiye alma (retrogresyon) ve farklı yeniden yaşlandırma (re-aging) (RRA) sürelerine bağlı ısıl işlemleri sırasında meydana gelen değişimler, sistematik olarak değerlendirildi. Bu ısıl işlem döngüsü RRA ısıl işleminin ilk basamağı olan yeniden çözeltiye alma (retrogression) işleminde numuneler 200 °C sıcaklıkta 10 dakika sürelerde bekletilerek hemen oda sıcaklığındaki suda soğutulup ardından argon atmosferi korumalı fırında 120 °C sıcaklıkta sırasıyla 2-4-8-16-24-32 saat yeniden yaşlandırma (re-aging) işlemi uygulanmaları ile tamamlanmıştır. Numunelerin makro sertlik ölçümü (HV1) ve SEM mikroyapı incelemeleri yapılmıştır. EDS ve maping analizleri yapılarak elementel dağılımlar gözlemlenmiştir. X-RD analizleri yapılarak düzlemler arası mesafe ve ısıl işlem süresine göre mikro gerinim değerleri hesaplanmıştır. Çökeltilerin yeniden yaşlandırma süresi arttıkça dağılımları da artmıştır. Yapılan çalışma sonucuna göre en yüksek sertlik değeri 24 saat RRA ısıl işlem yapılan ve en yüksek mikro gerinim 8 saat RRA yapılan malzemede görülmüştür.

Anahtar Kelimeler:

Al7075, RRA Isıl işlemi, Kristalografi

Investigation of RRA Heat Treatment Effects on Al - Zn - Mg - Cu Alloy Crystallography

In structural applications where strength, i.e. strength to weight ratio is the primary requirement, iron-based materials must be replaced by materials with similar properties. Heat-treatable 7075 aluminum alloy is considered one of the common interests of researchers due to its strength similar to that of steels and is widely used in automobile, aircraft industry and marine applications. Besides its high hardness and strength, it is one of the most important alloys of the defense industry with its lightness. In this study, the changes that occurred during the retrogression and different re-aging (RRA) times on heat treatments of the commercially purchased T651 heat treated Al - Zn - Mg - Cu alloy were systematically evaluated.This heat treatment cycle; The first step of the RRA heat treatment, the retrogression process (re-solution), the samples are kept at 200 ° C for 10 minutes and immediately cooled in water at room temperature and then in an argon atmosphere protected oven at 120 ° C for 2-4-8-16-24-32 hours respectively. -aging (re-aging) process has been completed with their application. SEM was used for microstructure studies and macro hardness measurement (HV1) of samples. EDS and map analysis were done and elemental distributions were observed. Micro strain values and the distance between planes were calculated by X-RD analysis.As the re-aging time of the sediments increased, their distribution increased. According to the results of the study, the maximum hardness value was seen in the material with RRA heat treatment for 24 hours.

Keywords:

Al7075, RRA Heat treatment, Crystallography,

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