Microstructural analysis of the stir zone of Al alloy produced by friction stir spot welding

This work mainly focuses on a series of microstructural analysis and predictions regarding dynamic recrystallization behavior, change in grain size, and dislocation density. Additionally, this study includes the shape prediction of the stir zone formed during friction stir spot welding. Microstructure analysis of the joint reveals that the mechanism of dynamic recrystallization in the stir zone is geometric dynamic recrystallization. A set of constitutive equations based on dislocation density is established and implemented in DEFORM-3D software to predict dynamic recrystallization during friction stir spot welding of AA6082. From the experimental and model predictions, it is observed that the original microstructure in the stir zone is completely replaced by a recrystallized fine grained microstructure. There is satisfactory agreement between the experimental grain size and the simulated results. In addition, the predicted shape of the stir zone fits quite well with the experimental shape as well.

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

Metals ◽

10.3390/met8110922 ◽

2018 ◽

Vol 8 (11) ◽

pp. 922 ◽

Cited By ~ 7

Author(s):

Xingwen Zhou ◽

Yuhua Chen ◽

Shuhan Li ◽

Yongde Huang ◽

Kun Hao ◽

...

Keyword(s):

Spot Welding ◽

Friction Stir Spot Welding ◽

Fracture Load ◽

Stir Zone ◽

Welding Parameters ◽

Al Alloy ◽

Ti Alloy ◽

Friction Stir ◽

2014 Al Alloy ◽

Al Coating

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.

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Friction Stir Spot Welding of AA2024-T3 with Modified Refill Technique

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.835.274 ◽

2020 ◽

Vol 835 ◽

pp. 274-287

Author(s):

Mahmoud Hussin Fahmy ◽

Hamed A. Abdel-Aleem ◽

Nahid Ahmed Abdel-Elraheem ◽

M.R. El-Kousy

Keyword(s):

Spot Welding ◽

Metal Flow ◽

Vertical Direction ◽

Friction Stir Spot Welding ◽

Weld Strength ◽

Al Alloy ◽

Exit Hole ◽

Two Stage ◽

Friction Stir ◽

Second Stage

The quality of welded joints of FSSW is mainly dependent on the processing parameters while the main disadvantage of this process is the creation of an exit hole. Process parameters, namely tool dimensions, tool rotational speed, and stir time were changed and their impact on bond dimensions and weld strength was investigated using 2024-T3 Al Alloy. Macro- and microstructures of the welded samples were examined; shear fracture loads were measured and the optimum set of operation variables was determined. To decrease the exit hole of the first stage the present paper proposes a modified two-stage weld-refill process employing the same welding machine. In this work, this two-stage process was referred to as reversed friction stir spot welding (ReFSSW). In the second stage, a smaller pin was used and the shoulder diameter was designed such that to force the metal of the upper plate to flow towards the exit hole of the first stage decreasing its dimensions. The metal flow in the second stage was evaluated by examining the microstructure of the metal that filled the exit hole of the first stage. Thin stir zone was found around the pin of the second stage followed by thermomechanically affected zone consisting of grains elongated in the vertical direction. The proposed process resulted in smaller exit hole dimensions and consequently higher mechanical properties compared with the conventional single-stage FSSW.

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