EBSD Technique Visualization of Material Flow in Aluminum to Steel Friction‐stir Dissimilar Welding

Abstract

Friction-stir welding (FSW), considered to be the most significant development in metal joining in a decade, has been the subject of much scientific interest and industrial application. Developed and patented in 1991 at The Welding Institute (TWI) in the UK, [1] the FSW joining process is based on extreme plastic deformation in the solid state and no associated bulk melting is involved. [2] Its application has been guided by a pressing industrial need, successfully applied to the joining of Al alloys, [3][4][5][6][7] and it appears to be a promising process for joining dissimilar alloys.In recent years, transportation systems have increasingly used light-weight materials, such as high strength steels, Al alloys and Mg alloys, to save energy and reduce pollution. The need to combine such different materials into a hybrid material system, e.g. car bodies and aircraft, is the force driving the development and improvement of welding techniques including FSW. Different concepts for tool materials [8][9][10][11] have lead to increasing interest in FSW of steels as well as of steel-based dissimilar welds.Compared to fusion welding techniques, solid-state welding processes such as FSW have particular advantages for joining dissimilar materials with very different melting intervals and large differences in physical and mechanical properties. [3,12] It has been shown that mild steels, [13] stainless steels [14][15][16] and high strength steels [17] can be friction-stir welded to Al alloys and that the comparatively low heat input characteristic of the process reduces or even prevents the formation of brittle intermetallic phases. [18][19][20] In FSW, the joint is created by frictional heating and associated stirring or forging action as the tool moves along the joint interface. Hence, tool geometry, welding parameters, joint design and the materials to be welded exert significant effects on the material flow pattern and temperature distribution. An understanding of the mechanical and thermal processes during FSW is needed for optimising process parameters and controlling the microstructure and properties of the joints.In particular, material flow and operating mechanisms during FSW are not fully characterised. These factors are, however, crucial to the optimisation of tool geometry and welding procedure that is necessary to obtain high structural efficiency welds. Thus, an increase in the number of approaches to investigating material flow during FSW has been observed in the literature. Reynolds et al. [21][22][23] used a marker insert technique to provide a qualitative characterisation of material flow metallographically. They described FSW as an in-situ extrusion process where the tool shoulder, the pin, the backing plate, and the cold base material form an extrusion die, where the hot material is extruded around both sides of the pin (leading and trailing) into the cavity being vacated by the pin as it moves forward. Complex material movement has also been analysed in dissimilar joints [24][25][26][27] and has been desc...

On the role of zinc on the formation and growth of intermetallic phases during interdiffusion between steel and aluminium alloys

“…In established rotational friction welding it is typically pushed out of the weld zone during the preheating friction-and the weld-cycles. In friction stir welding (FSW) in a butt joint configuration, sound welds between Zn-coated steel and Al alloys have been produced without interfacial failure [46][47][48]. Here the tool penetrated the steel only lightly and Zn was apparently scraped by the tool shoulder and mixed into the stir zone, but did not affect the intermetallic phase formation.…”

Interfacial Reaction during Friction Stir Welding of Al and Cu

“…However, for dissimilar welding, some authors have recently shown that both the position of the pin and the selection of the metal positioned on the advancing side may strongly influence the quality of the joint. [13,14,16,17,[25][26][27][28][29] For example, Lee and Jung managed to obtain void-free welds between a 6061 aluminum alloy and copper only by shifting the stirring pin toward the aluminum plate. [17] In the present study, a 1050 aluminum alloy was joined to commercially pure copper (99.9 pct) following this approach.…”

Microestrutura de uma Solda Dissimilar entre o Aço Inoxidável Ferrítico AISI 410S e o Aço Inoxidável Austenítico AISI 304L Soldado pelo Processo FSW

“…No início da década de 1990 foi desenvolvido no TWI (Inglaterra) um novo processo de soldagem por fricção denominado friction stir welding (FSW) [13], o qual tem sido considerado o mais significativo desenvolvimento em união de metais das últimas décadas, sendo um tema de grande interesse científico e com forte aplicação industrial [14].…”