Formability of Friction Stir-Welded Blanks with Different Thickness Ratios
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RODUCTION
FICRICTION stir welding (FSW) was introduced as a solid-state welding process in 1991 by The Welding Institute (TWI).[1] FSW is based on a simple process. A nonconsumable rotating tool that is based on a special design of pin and shoulder plunges into two edges of sheets or plates and moves forward to join them. The frictional work between the tool shoulder and the work piece makes the plastic deformation of materials that generates considerable heat.[2] As a solid-state joining process, FSW is capable of producing high-quality, defect-free welds even in a difficult-to-weld series of aluminum alloys.[3,4] A weld that is produced by FSW has higher strength and formability as a result of the relatively low welding temperature in comparison with the fusion welding processes. FSW shows strong potential for being replaced by the riveting and resistance spot welding of aluminum and steel sheets in the aerospace
SINA KOLAHGAR, Graduate, AMIR HOSSEIN KOKABI, Professor, and ABBAS AKBARZADEH, Associate Professor, are with the Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran. MORTEZA GHAFFARPOUR, Graduate, is with the Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran. Contact e-mail: ghaff[email protected] NILOUFAR HABIBI, Graduate, is with the School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran. Manuscript submitted April 5, 2013. Article published online February 17, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
and transport industries. In addition, FSW can be used to make tailor-welded blanks (TWBs). Introducing TWBs has revolutionized the sheet metal-forming concepts. Large banks with the preferential properties can be easily produced as dissimilar TWBs. One of the most crucial properties of a blank is the strength-to-weight ratio, which can considerably enhance the TWB process. Moreover, using TWBs reduces the production cost tremendously when the welding process is accomplished prior to the forming process.[5] Since welding sheets before forming mostly results in formability reduction, study of the formability behavior of TWBs is vital. The previous work on welding dissimilar sheets can be categorized into four main categories. The first category has considered FSW of different aluminum alloys[6–9]; the second one has focused on welding aluminum alloys to another sheet metal[10,11]; the third one has been about welding two heterogeneous metals[5]; and the last one has concentrated on FSW of homogenous aluminum alloy sheets with different thicknesses, which has been investigated less than the former groups.[5–15] There are some studies on the properties of TWBs with different thickness ratios (TRs) that admitted that the location of a fracture in specimens is regardless of the thickness ratio and always occurs in the heat-affected zone of the weld.[5,13] This implies that these regions suffer from low ductility; the forming procedure of TWBs has to be
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