Microstructure and Mechanical Properties of Dissimilar Friction Stir Welded AA2024-T4/AA7075-T6 T-Butt Joints

Mohamed M.Z Ahmed,Naser A Alsaleh,Sabbah Ataya,Mohamed M El-Sayed Seleman,Zeinab A Zidan,Rashad M Ramadan

doi:10.3390/met11010128

Mohamed M.Z Ahmed, Naser A Alsaleh + Show 4 more

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https://doi.org/10.3390/met11010128

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Abstract

Aircraft skin and stringer elements are typically fabricated from 2xxx and 7xxx series high strength aluminum alloys. A single friction stir welding (FSW) pass using a specially designed tool with shoulder/pin diameter ratio (D/d) of 3.20 is used to produce dissimilar T-butt welds between AA2024-T4 and AA7075-T6 aluminum alloys at a constant travel speed of 50 mm/min and different rotational speeds of 400, 600 and 800 rpm. The AA2024-T4 is the skin and the AA7075-T6 is the stringer. Sound joints are produced without macro defects in both the weld top surfaces and the joint corners at all rotational speeds used (400, 600, and 800 rpm). The hardness value of the nugget zone increases by increasing the rotational speed from 150 ± 4 Hv at 400 rpm to 167 ± 3 Hv at 600 rpm, while decreases to reach the as-received AA2024-T4 hardness value (132 ± 3 Hv) at 800 rpm. Joint efficiency along the skin exhibits higher values than that along the stringer. Four morphologies of precipitates were detected in the stir zone (SZ); irregular, almost-spherical, spherical and rod-like. Investigations by electron back scattered diffraction (EBSD) technique showed significant grain refinement in the sir zone of the T-welds compared with the as-received aluminum alloys at 600 rpm due to dynamic recrystallization. The grain size reduction percentages reach 85 and 90 % for AA2024 and AA7075 regions in the mixed zone, respectively. Fracture surfaces along the skin and stringer of T-welds indicate that the joints failed through mixed modes of fracture.

Highlights

Friction Stir Welding (FSW) is a solid-state welding technique, where similar [1,2,3]and dissimilar metals [2] are welded without reaching their melting point
Arora et al [20] reported that the hardness and tensile strength of the friction stir similar butt joint of AA2219 were lower than the base metal
Babu et al [18] studied the effect of pin profiles on the friction stir welded (FSWed) lap joint quality of the AA2014 aluminum alloy and reported that the strength and the failure mode of joints are related to the hook geometry

Summary

Introduction

Friction Stir Welding (FSW) is a solid-state welding technique, where similar [1,2,3]and dissimilar metals [2] are welded without reaching their melting point. Sadeesh et al [21] studied the influence of using five different tool designs in FSW of dissimilar AA2024 and AA6061aluminum alloys in butt joints and concluded that the joints efficiency is related to the varying welding process parameters and the shoulder to pin diameter ratio is the main dominant parameter. Manuel et al [22] investigated the behavior of the friction stir welds of three dissimilar aluminum alloys in a T-joint using three base materials namely, AA2017-T4, AA5083-H111, and AA6082-T6. They reported that the arrangement of the skin materials with respect to the pin rotation direction influence the morphology and the mechanical properties of the joints [22]. The formed dendritic structure during solidification in the fusion zone is significantly deteriorating the mechanical properties of the joints [5]

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