Friction Stir Spot Welding-Brazing of Al and Hot-Dip Aluminized Ti Alloy with Zn Interlayer

Abstract

Friction stir spot welding (FSSW) of Al to Ti alloys has broad applications in the aerospace and automobile industries, while its narrow joining area limits the improvement of mechanical properties of the joint. In the current study, an Al-coating was prepared on Ti6Al4V alloy by hot-dipping prior to joining, then a Zn interlayer was used during friction stir joining of as-coated Ti alloy to the 2014-Al alloy in a lap configuration to introduce a brazing zone out of the stir zone to increase the joining area. The microstructure of the joint was investigated, and the joint strength was compared with the traditional FSSW joint to confirm the advantages of this new process. Because of the increase of the joining area, the maximum fracture load of such joint is 110% higher than that of the traditional FSSW joint under the same welding parameters. The fracture load of these joints depends on the joining width, including the width of solid-state bonding region in stir zone and brazing region out of stir zone.optimize the mechanical properties of the joint [17][18][19][20][21]. Unavoidably, the traditional FSSW would leave a keyhole that reduces its bonding area [22]. Although some modified processes for FSSW, such as refill FSSW [23], flat FSSW [24], and short travel FSSW [25], have attempted to eliminate this visible keyhole, they are complicated and time-consuming owing to the rigorous welding conditions and/or complex tool design. Recently, friction stir brazing (FSSB) has been developed by using a pinless tool and adding brazing filler metal to induce metallurgical reaction at the interface with the aid of friction heat and forging pressure, instead of plastic flow [22]. This technique has successfully introduced a brazing zone in dissimilar joints of steel/Al [26], Cu/Al [27], and Al /Mg [28], while FSSB of Al and Ti alloys is yet to be reported.This work aims to find an effective approach to improve the joining area of the Al/Ti joint by combining FSSW and FSSB. Zinc (Zn) is an optional filler for FSSB of Al alloys as a result of its low melting point (420 • C), high solubility in Al, as well as absence of formation of IMCs in the Al-Zn alloying system [29][30][31][32]. During our preliminary study, a Zn interlayer was placed between the interface of 2014 Al and Ti6Al4V alloys for the FSSB process to determine their weldability. It was found that the high affinity of Ti towards oxygen led to the formation of non-protective oxide scales on the Ti6Al4V [33], resulting in poor wettability of Zn to Ti alloys and, therefore, failure to join Al and Ti alloys. Recently, using an electroplating process before the FSB process would produce a copper layer on the surface of graphite, which converted the graphite-copper lap joint to the similar joining of copper to copper [34]. This gives us an idea that pretreating the base metal will be a possible benefit for FSSB of Al and Ti.In the present paper, we utilized hot dip to aluminize T6Al4V alloys and developed a friction stir spot joining process, called friction stir spot w...

Dissimilar Metal Welding

“…This special issue of Metals covers sixteen articles [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] focused on dissimilar metal joining techniques. Some of the published reports have confirmed the increasing interest in solid state welding processes, in particular friction based welding [6][7][8][9][10] and electromagnetic pulse welding [11,12], due to benefits related to the properties and achievable microstructure, and to energy and environmental considerations. Other papers dealt with fusion welding techniques, mainly laser based [13][14][15][16], among others [5,17], and brazing processes [18,19].…”

“…In the latter, Eslami et al pointed out that an adjustment of the cross-section is required to realise electrical conductors free of resistive losses [9]. In [10], Zhou et al carried out friction stir spot welding-brazing of aluminium alloy and a hot-dip aluminized titanium alloy, using a Zn interlayer to extend the extremely narrow joining area, generally addressed as the main drawback of FSSW process. The formation of the brazing zone between the Al alloy and Al coating on Ti6Al4V alloy was successfully introduced by the addition of a Zn interlayer.…”

Investigation on Interface of CuW/Al Composite Using Ni Interlayer by Vacuum Hot-Pressing Diffusion Bonding

“…Finally, the interlayer should not generate IMCs with the base, or form less brittle IMCs. Many metals, such as nickel (Ni) [25], titanium (Ti) [26], zinc (Zn) [27], copper (Cu) [28], and silver (Ag) [29], have been considered as the constructive interlayers for the bonding in dissimilar metal composites. For example, Yang et al [30] investigated the influence of Ni interlayer on the interfacial reaction of Al/Mg joint.…”

Dislocation Density-Based Modeling of Dynamic Recrystallized Microstructure and Process in Friction Stir Spot Welding of AA6082

“…Lightweight structures have attracted increasing attention in the automobile and aerospace industries to enhance performance efficiency as well as to reduce environmental impact [1][2][3]. More weight saving material such as aluminum alloy is utilized instead of steel in vehicle design.…”