AA6082-T6 alloy was joined by friction stir spot welding using five different pin profiles, such as a cylindrical, conical, triangular, hexagonal and cylindrical with two grooves, at different dwell time. The joints welded by cylindrical pins had larger effective weld width. But, grooves on the cylindrical pin decreased the effective weld width. The hook was bent downward from the interface of the sheets in the weld made with hexagonal pin, which had the smallest effective weld width. When conical pin was used, effective weld width increased with increasing the dwell time. In the case of using tools with cylindrical and conical pins, HAZ hardness was relatively lower. With increasing dwell time, HAZ hardness of the joints made with conical pin decreased. Effective weld width determined the weld strength under the tensile shear loading condition: Larger effective weld width resulted in higher weld strength. Weld strength of the joints made with cylindrical pin was higher. The joints fabricated with hexagonal pin had the lowest weld strength. In general, higher dwell time led to higher weld strength. The welds with the higher strength experienced both brittle and ductile fractures, while the joints with the lower strength exhibited completely brittle fracture.
Çift fazlı DP (Dual Fazlı) çelikleri otomotiv sanayinde en çok tercih edilen çelik gruplarındandır. Kullanımları sırasında bu çeliklerin yükleme yönüne göre hadde yönü ve deformasyon hızı son derece önem arz etmektedir. Bu çalışmada, DP450 ve DP800 çift fazlı çeliklerinde deformasyon hızı ve haddeleme yönüne bağlı olarak çekme sonuçları incelenmiştir. Deneysel çalışmalarda, haddeleme yönünün çekme ekseniyle yaptığı açılar 0°, 45° ve 90°, deformasyon hızları 2.4x10-4, 2.4x10-3, 2.4x10-2 ve 1.2x10-1 s-1 olarak belirlenmiştir. Çalışmada elde edilen sonuçlar göstermiştir ki, DP450 ve DP800 çeliklerinde deformasyon hızının çekme özellikleri üzerindeki etkisi hadde yönü etkisinden daha fazla olmuştur. Her iki çelikte de deformasyon hızı artışı ile akma ve çekme mukavemeti değerleri artmış, kopma uzaması değerleri ise önemli ölçüde düşmüştür. Ayrıca, her iki çelikte de deformasyon hızının akma mukavemeti üzerindeki etkisi çekme mukavemeti üzerindeki etkisinden daha fazla olmuştur. DP800 çeliğinde deformasyon hızı ile mukavemet artış oranı DP450 çeliğine nazaran daha düşük kalırken, kopma uzaması düşüş oranı ise daha fazla olmuştur. Hadde yönünün etkisine bakıldığında ise, DP450 ve DP800 çeliklerinde 45° hadde yönünde nispeten daha yüksek mukavemet değerleri gözlenirken aynı hadde yönünde daha düşük uzama değerleri elde edilmiştir.
Dual Phase (DP) steels are the most commonly used steels in the automotive industry to reduce vehicle weight and improve car safety. DP600 steel is one of the most used steels for the automotive industry because this steel has high strength and good elongation properties. During the manufacture of automotive parts, welding is the most commonly used joining process, and especially the laser welding is getting more and more importance. This study was executed to evaluate how the welding type (single-sided and double-sided) affects the tensile properties of Nd:YAG (Neodymium-Doped Yttrium Aluminum Garnet; Nd:Y3Al5O12) laser welded DP600 steel sheets using different pulse frequencies. The laser welded samples were investigated by the methods of tensile test and fractography. Experimental results indicated that the tensile properties varied significantly depending on the welding type and pulse frequency. The tensile properties of the double-sided laser welded joints were significantly higher than those of the single-sided laser welded joints. Tensile strength and elongation of the single-sided and the double-sided laser welded joints increased almost linearly with increasing pulse frequency. The higher pulse frequency resulted in larger fully bonded section size, which led to higher tensile properties. The maximum tensile strength and elongation (611 MPa and 10.06 %) were obtained with the double-sided laser welded joint in the pulse frequency of 8.5 Hz. The tensile strength of this joint was almost equal to that of the base metal, but its elongation value was lower that of the base metal.
Dual-phase (DP) steel sheets are the most widely used steel group in the automotive industry. When these steel sheets are used in car body components, welding is inevitably needed during the manufacturing process. Although the resistance spot welding (RSW) is the most widely used welding method in the automotive industry, the newly popular laser welding has gained more importance in the welding of these steel grades in recent years. In this work, the DP600 and DP1000 steel sheets were joined as double-sided with the pulsed Nd: YAG (Neodymiumdoped Yttrium Aluminum Garnet (Y3Al5O12)) laser welding. Performing similar or dissimilar weld of DP steel sheets is an inevitable demand in the modern automotive industry. So, in this study similar (DP600-DP600, DP1000-DP1000) and dissimilar (DP600-DP1000) steel sheets were welded in the flat position with the butt joint. In order to evaluate welding performance, microstructural studies and mechanical tests were performed, and experiments carried out in this context include optical microscope studies, tensile tests and Vickers microhardness measurements. The tensile strength of the similar welded joints is a little bit lower than the base metals (BM). But, for dissimilar weld, the tensile strength is even lower than DP600-DP600 joint. And the microstructure of the welded joints are composed of martensite, retained austenite and bainite in the fusion zone and a mixture of martensite, bainite, ferrite, retained austenite and tempered martensite in heat affected zone (HAZ).
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