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This paper presents the use of the stiffness matrix method based on the first order shear deformation theory to predict the fundamental natural frequencies and buckling loads of noncylindrical unidirectional composite helical springs subjected to initial static axial force and moment. This theoretical study about such springs with circular/rectangular cross sections and large pitch angles is performed first time in the literature. The validity of the present results is verified by the benchmark studies related with initially compressed isotropic cylindrical springs.

Aluminum alloys of the 7xxx series (AA7075) are preferred in the aerospace and automotive industries due to their low densities, high strength, good corrosion resistance properties. Additionally, these alloys show the most effective aging properties among aluminum alloys. For this reason, it is very important to determine the most appropriate aging parameters for microstructural development. Literature review reveals that the effect of pre-strain on springback has not been studied yet. In this study, the effects of aging temperature, time, and pre-strain on mechanical properties are investigated for AA7075. Precipitates present in solid solutions of AA7075 and their effects are examined. Results reveal that MgZn 2 precipitation is not observed at aging temperatures of 120 and 160 ºC. After the formation of MgZn 2 precipitates, microstructure becomes softer when aging continues at a higher temperature or longer period of time. It is clearly seen that pre-strain causes Portevin-Le Chatelier (PLC) effect after aging at 120 and 160 ºC for aging times of 30 and 90 minutes.

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ÖZETMagnezyum alaşımlarının havacılık, uzay ve otomotiv endüstrisinde yapısal malzeme olarak kullanımı gün geçtikçe artmaktadır. Henüz yaygın kullanımda olmaması ve üretiminin pahalı olması nedeniyle üreticilerin sayısı demir ve çelik üreticilerine göre çok daha azdır. Bu durum magnezyum alaşımlarının pahalı olmasının temel sebeplerinden biridir. Bu çalışmada, magnezyum ve alaşımlarının imalat yöntemleri, şekillendirilebilirlik, korozyon direnci, çevreye olan etkileri ve mevcut kullanım alanları incelenmiştir.Anahtar Kelimeler: Magnezyum, magnezyum alaşımları, hafif malzemeler. INVESTIGATION OF MAGNESIUM ALLOYS AND THEIR APPLICATIONS ABSTRACTThe use of magnesium alloys in aerospace, space, and automotive industry as structural materials has gradually been increased. Magnesium alloys producers are much less than the iron and steel producers in number due to the alloys are still not widely used and their production cost are high. This is one of main reasons that the prices of the alloys are expensive. In this study, the manufacturing techniques, formability, corrosion resistance, environmental effects of magnesium and its alloys and applications were investigated.