Nd:YAG Lazer Kaynağı ile Birleştirilen Farklı Türdeki DP600-DP1000 Çeliklerinde Mekanik ve Mikroyapı Özellikleri

Bu çalışmada DP600 ve DP1000 çelik sacları darbeli Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet (Y3Al5O12)) lazer kaynağı ile birleştirilmiş ve farklı türdeki sacların kaynağında mekanik ve mikro yapı özellikleri deneysel olarak incelenmiştir. Bilindiği gibi modern otomotiv endüstrisinde farklı türdeki DP çeliklerimin birleştirilmesine talep vardır. Lazer kaynak işleminde kaynak parametrelerinin seçimi kaynak nihai özelliklerini önemli ölçüde etkiler. Bu yüzden bu çalışmanın amacı Nd:YAG lazer kaynaklı DP600- DP1000 çeliklerinde darbe frekansının mekanik özelliklere etkilerinin belirlenmesidir. Bu amaçla farklı türdeki (DP600-DP1000) çelik saclar çift taraflı olarak alın kaynağı ile birleştirilmiştir. Kaynak performansını analiz etmek için mikro yapı çalışmaları, çekme testleri ve mikro sertlik ölçümleri gerçekleştirilmiştir. Kaynak kesitinde temel malzeme, ısı tesiri altındaki bölge ve ergime bölgesinden oluşan 3 farklı makro yapısal bölge ortaya çıkmıştır. Ayrıca DP1000 tarafında ısı tesiri altındaki bölge ile temel malzeme arasında bir geçiş bölgesi gözlenmiştir. Yüksek darbe frekansı derin penetrasyon ve daha geniş ergime bölgesi ve ısı tesiri altındaki bölgeye neden olmuştur. Dolgu teli olmadan gerçekleştirilen kaynaklar ergime bölgesinde makro gözenekler içermektedir. Kaynaklı birleştirmenin mukavemeti darbe frekansındaki artışla beraber önemli ölçüde artmıştır. Bu çalışmada elde edilen çekme mukavemetleri otomotiv endüstrisi için oldukça tatmin edicidir. Ergime bölgesi en yüksek mikro sertlik özelliklerine sahiptir. Fakat DP1000 geçiş bölgesinde temel malzemeden daha düşük sertlik değerleri ölçülmüştür.

Microstructural and Mechanical Properties of Nd:YAG Laser Welded Dissimilar DP600-DP1000 Steel Sheets

In this study, the DP600 and DP1000 steel sheets were joined with the pulsed Nd:YAG (Neodymium-dopedYttrium Aluminum Garnet (Y3Al5O12)) laser welding and, mechanical and microstructure properties ofthe dissimilar welds were experimentally investigated. As known, there is a demand in modern automotiveindustry for performing dissimilar weld of DP steel sheets. In the laser welding operation, the selection ofwelding parameters affects the final properties of welds substantially. So, the main aim of this study wasdetermining the influence of pulse frequency on the mechanical properties of pulsed Nd:YAG laser weldedDP600-DP1000 steel sheet joints. For this purpose, dissimilar (DP600-DP1000) steel sheets were doublesidedwelded with the butt joint. To analyze the welding performance, microstructural studies, tensiletests and microhardness measurements were carried out. The weld cross-sections of the joints revealedthree main distinct macrostructural zones: Base metal and heat affected zone of both steels, and fusionzone. Moreover, a transition zone was observed between the base metal and heat affected zone on theDP1000 sides. Higher pulse frequency led to deeper penetration and larger fusion zone and heat affectedzone. The laser welded joints without filler material had macro porosities in the fusion zones. The tensilestrength of the joints significantly increased with increasing pulse frequency. The tensile strengthsobtained in this study may be quite satisfactory for automotive industrial applications. Fusion zone hadthe highest microhardness values. However, the lower microhardness values than base material weremeasured in the transition zone on DP1000 side.

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