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Open AccessArticle

Fatigue Life Assessment of Refill Friction Stir Spot Welded Alclad 7075-T6 Aluminium Alloy Joints

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Department of Manufacturing and Production Engineering, Rzeszow University of Technology, al. Powst. Warszawy 8, 35-959 Rzeszów, Poland
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Institute of Technology, Faculty of Mathematics and Natural Sciences, University of Rzeszów, al. Rejtana 16c, 35-959 Rzeszow, Poland
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Department of Materials Forming and Processing, Rzeszow University of Technology, al. Powst. Warszawy 8, 35-959 Rzeszów, Poland
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Centre for Innovative Technologies, University of Rzeszów, ul. Pigonia 1, 35-959 Rzeszów, Poland
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Institute of Technology and Material Engineering, Faculty of Mechanical Engineering, Technical University of Košice, Mäsiarska 74, 040 01 Košice, Slovakia
*
Author to whom correspondence should be addressed.
Metals 2020, 10(5), 633; https://doi.org/10.3390/met10050633
Received: 3 April 2020 / Revised: 6 May 2020 / Accepted: 12 May 2020 / Published: 13 May 2020
(This article belongs to the Special Issue Forming Processes of Modern Metallic Materials)
Refill Friction Stir Spot Welding (RFSSW) shows great potential to be a replacement for single-lap joining techniques such as riveting or resistance spot welding used in the aircraft industry. In this paper, the fatigue behaviour of RFSSW single-lap joints is analysed experimentally in lap-shear specimens of Alclad 7075-T6 aluminium alloy with different thicknesses, i.e., 0.8 mm and 1.6 mm. The joints were tested under low-cycle and high-cycle fatigue tests. Detailed observations of the fatigue fracture characteristics were conducted using a scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS). The locations of fatigue failure across the weld, fatigue crack initiation, and propagation behaviour are discussed on the basis of the SEM analysis. The possibility of predicting the propagation of fatigue cracks in RFSSW joints is verified based on Paris’s law. Two fatigue failure modes are observed at different load levels, including shear fracture mode transverse crack growth at high stress-loading conditions and at low load levels, and destruction of the lower sheet due to stretching as a result of low stress-loading conditions. The analysis of SEM micrographs revealed that the presence of aluminium oxides aggravates the inhomogeneity of the material in the weld nugget around its periphery and is a source of crack nucleation. The results of the fatigue crack growth rate predicted by Paris’s law were in good agreement with the experimental results. View Full-Text
Keywords: aircraft industry; aluminium alloy; friction stir spot welding; mechanical engineering; single-lap joints aircraft industry; aluminium alloy; friction stir spot welding; mechanical engineering; single-lap joints
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MDPI and ACS Style

Kubit, A.; Drabczyk, M.; Trzepiecinski, T.; Bochnowski, W.; Kaščák, Ľ.; Slota, J. Fatigue Life Assessment of Refill Friction Stir Spot Welded Alclad 7075-T6 Aluminium Alloy Joints. Metals 2020, 10, 633.

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