ZM21 MAGNEZYUM ALAŞIMININ HADDELEME SONRASI MİKRO YAPI VE MEKANİK ÖZELLİKLERİNİN İNCELENMESİ
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2020-07-24
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info:eu-repo/semantics/openAccess
Özet
Bu çalışmada, indüksiyon ocağında ZM21 magnezyum alaşımının Y şeklindeki blok kalıba dökümü gerçekleştirilmiştir. Kalıbın soğuma hızına bağlı olarak uygun yerlerinden aynı mikroyapıya sahip plakalar kesilmiştir. Daha sonra 400°C’de 16 saat homojenizasyon tavı uygulanmıştır. 275°C, 325°C ve 375°C’ de farklı hadde oranlarında (%40, %60 ve %80) ve ? = 0.2’lik sabit deformasyon derecesinde 4,7 m/d hadde hızında haddelenerek farklı kalınlıklardan (10mm, 6mm ve 3,3mm) 2mm kalınlığa indirgenmiştir. Haddeleme işlemi sonrası 2mm’lik levhaların yüzeylerine yüzey pürüzlülüğü testi ve penetrant testi uygulanmıştır. Mikroyapısal iyileşme ve tane boyutunun daha kolay hesaplanabilmesi için haddelenmiş levhalardan alınan numuneler 260°C’de 30 dk kısa tavlamaya tabi tutulduktan sonra optik mikroskop ve SEM incelemeleri gerçekleştirilmiştir. Mekanik testler için Vicker’s sertlik yöntemi ve oda sıcaklığında çekme testi uygulanmıştır. Çekme testi sonrası kırık yüzeylerin morfolojisi SEM ile incelenmiştir. Sonuçlar incelendiğinde, işlem görmemiş numuneye oranla homojenizasyon ve haddeleme sonrası sertlik değerlerinde artış gözlenmiştir. Hadde oranı artmasıyla yapı daha homojen bir görünüm kazanmıştır. En ince tane boyutu 13,03 µm ile 325°C’de %80 hadde oranında gözlenmiştir. Homojenleştirme sonucu tane boyutunun azalması ve Mg-Zn ikincil fazlarının yerini ?-Mg fazına bırakmasıyla akma ve çekme dayanımı %21 ve %2,1 oranlarında artarken, uzama oranında ise %2,9 oranında düşüş gözlenmiştir. Homojenizasyon işlemi görmüş numuneler ve 275ºC’de haddelenmiş numuneler sünek kırılma davranışı sergilerken, 325ºC ve 375ºC’de haddelenmiş numuneler hem ikincil faz oluşturabilecek elementlerin belirli bölgelerde yoğunlaşması hem de yüzeydeki oyukların da azalmasıyla gevrek kırılma davranışı sergilemişlerdir.
In this study, ZM21 magnesium alloy were cast to the Y-form mold in induction furnace. Depending on the cooling rate of the mold, plates having the same microstructure were cut from their appropriate locations. After that, homogenisation annealing was applied at 400°C for 16 hours. Rolled at different rates (40%, 60% and 80%) at 275°C, 325°C and 375°C with a constant deformation of ? = 0.2 at a rate of 4.7 m/min. (10mm, 6mm and 3,3mm) to 2mm thickness. Surface roughness test and penetrant test were applied to the surfaces of 2 mm plates after the rolling process. For microstructural improvement and easier calculation of grain size, samples taken from rolled plates were subjected to short annealing at 260°C for 30 minutes and optical microscope and SEM examinations were performed. Vicker’s hardness method and tensile test at room temperature were applied for mechanical tests. After the tensile test, the morphology of the fracture surfaces was examined with SEM. When the results were examined, an increase in the hardness values after homogenization and rolling compared to the as-cast sample was observed. It was observed that the structure gained a more homogeneous appearance with the increase of the rolling rate. The finest grain size was observed with a ratio of 13,03 ?m and a rolling rate of 325 ºC at 80%. After homogenization process, with the decrease of grain size and replacement of the Mg-Zn secondary phases to the ?-Mg phase, yield and tensile strength were increased by %21 and %2,1, respectively while the elongation was decreased by %2,9. Samples with homogenization treatment and samples rolled at 275ºC exhibit ductile fracture surfaces, while samples rolled at 325ºC and 375ºC exhibit brittle fracture behavior, both by condensing the elements that can form secondary phases in certain regions and by decreasing cavities at surface."
In this study, ZM21 magnesium alloy were cast to the Y-form mold in induction furnace. Depending on the cooling rate of the mold, plates having the same microstructure were cut from their appropriate locations. After that, homogenisation annealing was applied at 400°C for 16 hours. Rolled at different rates (40%, 60% and 80%) at 275°C, 325°C and 375°C with a constant deformation of ? = 0.2 at a rate of 4.7 m/min. (10mm, 6mm and 3,3mm) to 2mm thickness. Surface roughness test and penetrant test were applied to the surfaces of 2 mm plates after the rolling process. For microstructural improvement and easier calculation of grain size, samples taken from rolled plates were subjected to short annealing at 260°C for 30 minutes and optical microscope and SEM examinations were performed. Vicker’s hardness method and tensile test at room temperature were applied for mechanical tests. After the tensile test, the morphology of the fracture surfaces was examined with SEM. When the results were examined, an increase in the hardness values after homogenization and rolling compared to the as-cast sample was observed. It was observed that the structure gained a more homogeneous appearance with the increase of the rolling rate. The finest grain size was observed with a ratio of 13,03 ?m and a rolling rate of 325 ºC at 80%. After homogenization process, with the decrease of grain size and replacement of the Mg-Zn secondary phases to the ?-Mg phase, yield and tensile strength were increased by %21 and %2,1, respectively while the elongation was decreased by %2,9. Samples with homogenization treatment and samples rolled at 275ºC exhibit ductile fracture surfaces, while samples rolled at 325ºC and 375ºC exhibit brittle fracture behavior, both by condensing the elements that can form secondary phases in certain regions and by decreasing cavities at surface."
Açıklama
Anahtar Kelimeler
ZM21 magnesium alloy, hot rolling, microstructure, mechanical properties, microstructure., ZM21 magnezyum alaşımı, haddeleme, mekanik özellikler, mikro yapı.
