Farklı alaşım elementi ilaveli WE43 magnezyum alaşımlarının döküm ve ekstrüzyon sonrası mikroyapı, mekanik ve korozyon özelliklerinin incelenmesi
Küçük Resim Yok
Tarih
2020
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Karabük Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Bu çalışmada, magnezyum alaşımlarının özel bir serisi olan WE serisine ait WE43 (W: İtriyum, E: Nadir Toprak Elementleri) magnezyum alaşımları incelenmiştir. Dökümler, WE43 alaşımına belirli oranlarda farklı alaşım elementleri ilave edilerek düşük basınçlı döküm yöntemiyle gerçekleştirilmiş olup, CO2 (hac.%99) ve SF6 (hac.%1) gaz karışımından oluşan koruyucu atmosfer altında gerçekleştirilmiştir. WE43 magnezyum alaşımlarına ilave edilen elementler, her biri ağ.% 0,2-0,5 ve 1 oranlarında olmak üzere Zn, Ca, Sn ve Sr olmuştur. Dökümlerin ardından, mikroyapılardaki tane sınırlarında yoğun olarak bulunan intermetalik fazları parçalamak ve çözündürmek amacıyla alaşımlara 525°C'de 8 saat süre ile homojenizasyon ısıl işlemi uygulanmıştır. Sonrasında her bir alaşımdan çıkarılıp işlenen biyetler 400 °C sıcaklıkta 16:1 ekstrüzyon oranıyla ve 0,3 mm/s ekstrüzyon hızında ekstrüze edilmiştir. Tüm alaşımların döküm, homojenizasyon ve ekstrüzyon sonrası mikroyapı incelemeleri gerçekleştirilmiştir. Yapılan incelemelerde WE43 alaşımına ilave edilen farklı alaşım elementlerinin kendilerine özgü farklı ikincil fazlar oluşturduğu ve bu ikincil fazların davranışlarının da birbirinden farklı olduğu tespit edilmiştir. Döküm konumunda en ince tane dağılımı artan ağ.%Ca ile elde edilirken, ekstrüzyon konumunda ise artan %Sr ilavesiyle gerçekleşmiştir. Alaşımların ekstrüzyon konumundaki mikroyapıları tamamı dinamik olarak rekristalize olmuş çift modlu tane yapılarından meydana gelmektedir. Hidrolik presin teknik limitinden ötürü yüksek ekstrüzyon sıcaklıklarında çalışıldığından dolayı rekristalize olmuş tanelerin büyük bir kısmı büyüyerek eşeksenli taneleri oluşturmuştur. Ekstrüzyon yönünde uzamış olan ikincil faz partikülleri etrafında çekirdeklenen ?-Mg taneleri ise bu fazların etrafında kümeler halinde kalmıştır. Mekanik özelliklerden sertlik yönüyle en yükek değerlere sahip alaşımlar WE43-1Zn ve WE43-1Ca alaşımlarıdır. Çekme testleri döküm ve ekstrüzyon konumları için hem oda sıcaklığında hem de 200 °C'de gerçekleştirilmiştir. Bu testler neticesinde döküm konumunda her iki test sıcaklığında da en yüksek akma, çekme mukavemeti ve % uzama değerlerine sahip alaşım WE43-1Zn olurken, ekstrüzyon sonrasındaki testlerde WE43-1Zn'nin yanı sıra WE43-1Ca alaşımı da ön plana çıkmıştır. Korozyon özelliklerinin en iyi olduğu WE43 alaşımı serisi Zn ilaveliler iken, içerdiği intermetalik türünden dolayı Ca ilaveli WE43 serisinin korozyon özellikleri oldukça zayıf bulunmuştur. Aşınma dayanımları alaşımların sertlik özellikleri ile paralel davranış sergilemiştir.
In this study, WE43 (W: Yttrium, E: Rare Earth Elements) magnesium alloys belonging to the WE series, which is a special series of magnesium alloys, were investigated. Castings were carried out by low pressure die casting method by the addition of different alloying elements to the WE43 alloy in certain proportions, and were carried out under a protective atmosphere consisting of a mixture of CO2 (99% by volume) and SF6 (1% by volume) gases. The elements added to the WE43 magnesium alloys were Zn, Ca, Sn and Sr, each in the ratio of 0.2-0.5 and 1 wt%. After casting, homogenization heat treatment was applied to the alloys at 525 °C for 8 hours in order to break up and dissolve the intermetallic phases that are densely formed along the grain boundaries in the microstructures. Afterwards, machined billets from each alloy were extruded at 400 °C at an extrusion rate of 16:1 and at an extrusion speed of 0.3 mm/s. Microstructural observations after casting, homogenization and extrusion processes were carried out for all the alloys. In these investigations, it has been determined that different alloying elements added to the WE43 alloy resulted in a formation of unique secondary phases and the behaviors of these secondary phases also differed from each other. While the finest particle distribution for as-cast alloys was achieved with increasing Ca content, it was realized with increasing Sr additions among the as-extruded alloys. The microstructures of the as-extruded alloys are composed of dynamically recrystallized bimodal grain structures. Due to the technical limitation of the hydraulic press, most of the recrystallized grains have grown to form equiaxed grains, since they were processed at high temperatures. The ?-Mg grains nucleated around secondary phase particles elongated in the extrusion direction remained in clusters around these phases. WE43-1Zn and WE43-1Ca alloys had the highest mechanical properties in terms of hardness. Tensile tests were carried out both at room temperature and 200 °C for as-cast and as-extruded alloys. As a result of these tests, the alloy with the highest yield, tensile strength and % elongation values at both test temperatures in the as-cast alloys was observed for WE43-1Zn, while WE43-1Ca alloy came to the fore in the as extruded samples as well as WE43-1Zn. While the WE43 magnesium alloy with the best corrosion properties were found after Zn additions, the corrosion properties of the Ca-added WE43 series were found to be quite poor due to the present intermetallic types. The wear resistance behavior of the alloys were in parallel with the hardness properties of WE43 alloys.
In this study, WE43 (W: Yttrium, E: Rare Earth Elements) magnesium alloys belonging to the WE series, which is a special series of magnesium alloys, were investigated. Castings were carried out by low pressure die casting method by the addition of different alloying elements to the WE43 alloy in certain proportions, and were carried out under a protective atmosphere consisting of a mixture of CO2 (99% by volume) and SF6 (1% by volume) gases. The elements added to the WE43 magnesium alloys were Zn, Ca, Sn and Sr, each in the ratio of 0.2-0.5 and 1 wt%. After casting, homogenization heat treatment was applied to the alloys at 525 °C for 8 hours in order to break up and dissolve the intermetallic phases that are densely formed along the grain boundaries in the microstructures. Afterwards, machined billets from each alloy were extruded at 400 °C at an extrusion rate of 16:1 and at an extrusion speed of 0.3 mm/s. Microstructural observations after casting, homogenization and extrusion processes were carried out for all the alloys. In these investigations, it has been determined that different alloying elements added to the WE43 alloy resulted in a formation of unique secondary phases and the behaviors of these secondary phases also differed from each other. While the finest particle distribution for as-cast alloys was achieved with increasing Ca content, it was realized with increasing Sr additions among the as-extruded alloys. The microstructures of the as-extruded alloys are composed of dynamically recrystallized bimodal grain structures. Due to the technical limitation of the hydraulic press, most of the recrystallized grains have grown to form equiaxed grains, since they were processed at high temperatures. The ?-Mg grains nucleated around secondary phase particles elongated in the extrusion direction remained in clusters around these phases. WE43-1Zn and WE43-1Ca alloys had the highest mechanical properties in terms of hardness. Tensile tests were carried out both at room temperature and 200 °C for as-cast and as-extruded alloys. As a result of these tests, the alloy with the highest yield, tensile strength and % elongation values at both test temperatures in the as-cast alloys was observed for WE43-1Zn, while WE43-1Ca alloy came to the fore in the as extruded samples as well as WE43-1Zn. While the WE43 magnesium alloy with the best corrosion properties were found after Zn additions, the corrosion properties of the Ca-added WE43 series were found to be quite poor due to the present intermetallic types. The wear resistance behavior of the alloys were in parallel with the hardness properties of WE43 alloys.
Açıklama
Lisansüstü Eğitim Enstitüsü, Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
Anahtar Kelimeler
Metalurji Mühendisliği, Metallurgical Engineering ; Mühendislik Bilimleri
