Mechanical and corrosion properties of friction stir welded joints of Al-Cu alloy 2219-T87

G. Srinivasa Rao; V. V. Subba Rao; S. R. Koteswara Rao

doi:10.3139/120.110775

Published by De Gruyter August 31, 2015

Mechanical and corrosion properties of friction stir welded joints of Al-Cu alloy 2219-T87

Mechanische und korrosive Eigenschaften von rührreibgeschweißten Verbindungen der Al-Cu-Legierung 2219-T87

G. Srinivasa Rao , V. V. Subba Rao and S. R. Koteswara Rao

From the journal Materials Testing

https://doi.org/10.3139/120.110775

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Abstract

In the present study, 8.1 mm thick AA 2219–T87 plates were joined by friction stir welding (FSW) process. Welds were characterized by using micro hardness survey, tensile testing, face bend, root bend tests, optical microscopy (OM), transmission electron microscopy (TEM) and salt fog test (ASTM B117) at different pH values and spraying times. Hardness survey across the joint revealed that weld nugget is the softest region and it is also found that tensile failure occurs in the nugget. Tensile testing of the transverse welded joints showed that high efficiency (> 75 %) joints could be produced. The friction stir welds subjected to the surface bend showed 1800 bend ductility, whereas in the critical root bend the cracks were initiated at a bend angle in the range of 30–40⁰. Transmission electron micrographs obtained from various regions of the weld indicated that almost all strengthening precipitates dissolved in the nugget region while partial dissolution of precipitates occurred in the thermomechanically affected zone and coarsening occurred in heat affected zone. However, the losses in hardness in the nugget due to dissolution of precipitates and the negation of work hardening by recrystallization were compensated to a large extent by the strengthening due to the grain refinement in the nugget, which explains the high joint efficiencies exhibited by these welds. It was observed that the welds possessed much better corrosion resistance in basic and neutral solution than in acidic solution. It was found that corrosion attack was greater in the base material than in weld metal at all pH values and spraying times. It has been concluded that friction stir welding has a significant effect on mechanical and corrosion properties of the welds.

Kurzfassung

In der Studie wurden 8,1 mm dicke AA 2219-T87 Platten mittels Rührreibschweißen (FSW) verbunden. Die Schweißnähte wurden mit Hilfe Mikrohärtemessungen, Zugversuche, Oberflächenbiegetests und Wurzelbiegetests, optische Mikroskopie (OM), Transmissionselektronenmikroskopie (TEM) und Salznebeltest (ASTM B117) bei verschiedenen pH-Werten und Sprühzeiten charakterisiert. Härtemessungen der Verbindung zeigten, dass die Schweißlinse die weichste Region ist und das Versagen in der Schweißlinse auftritt. Die Zugprüfung der Querschweißverbindungen wiesen auf eine hohe Effizienz (> 75 %) hin. Die Rührreibschweißungen, die mit dem Oberflächenbiegetest geprüft wurden, zeigten eine Biegeduktilität von 180°, während in der kritischen Wurzelbiegung die Risse bei einem Biegewinkel von 30° bis 40° auftraten. TEM-Aufnahmen aus verschiedenen Bereichen der Schweißung stellten fest, dass nahezu alle festigkeitssteigernden Ausscheidungen im Bereich der Schweißlinse gelöst sind, während teilgelöste Ausscheidungen in der thermomechanisch beeinflussten Zone und Vergröberung in der WEZ auftraten. Jedoch werden die Härteverluste in der Schweißlinse aufgrund der Auflösung von Ausscheidungen und der Aufhebung der Kaltverfestigung durch Umkristallisation zu einem großen Teil durch Verfestigung durch Kornfeinung in der Schweißlinse kompensiert. Dies erklärt die hohe Verbindungseffizienz dieser Schweißungen. Es wurde beobachtet, dass die Schweißungen eine ausgezeichnete Korrosionsbeständigkeit in basischer und neutraler Lösung aufweist, dagegen eine niedrigere in saurer Lösung. Es wurde ermittelt, dass der Korrosionsangriff bei allen pH-Werten und Sprühzeiten im Grundmaterial größer als im Schweißgut ist. Es wurde daraus geschlossen, dass das Rührreibschweißen eine signifikante Wirkung auf die mechanischen und korrosiven Eigenschaften der Schweißverbindungen hat.

§Correspondence Address, G. Srinivasa Rao, Associate Professor, Department of Mechanical Engineering, SRM University, NCR Campus, Delhi, India-201204. E-mail: gsrinu1882@gmail.com

Associate Prof. G. Srinivasa Rao, born in 1981, completed his M. Tech. in Production Engineering at Acharya Nagarjuna University Guntur, India. He worked as Assistant Professor at ASIST, AP, India from October 2007 to June 2009. Then he worked as Assistant Professor in Tagore Engineering College, Chennai, India from June 2009 to May 2013. He worked as Associate Professor and headed the Department of Mechanical Engineering, ASIST, Paritala, India from June 2013 to June 2015. Since July 2015, he is working as Associate Professor in the Department of Mechanical Engineering, SRM University, Delhi, India. He is pursuing his PhD in the Faculty of Mechanical Engineering at JNT University, A.P, India.

Professor V. V.S ubba Rao, born in 1968, received his PhD in Metallurgical and Materials Engineering from IITK, Kharagpur, India in 2004. He completed his post doctoral studies in South Korea. He has published more than 30 publications in international journals so far. He has around 21 years of professional experience in teaching and research. Presently, he is working as Professor in the Department of Mechanical Engineering, JNTUK, Kakinada, A.P, India.

Prof. S. R. Koteswara Rao, born in 1966, received his PhD in Metallurgical and Materials Engineering from IIT Madras, Chennai, India in 2005. He has published more than 35 papers in international journals so far. He has around 20 years of professional experience in teaching and research. Currently, he is working as Professor of Mechanical Engineering at SSN College of Engineering, Chennai, Indiaa.

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Published Online: 2015-08-31

Published in Print: 2015-09-01

Mechanical and corrosion properties of friction stir welded joints of Al-Cu alloy 2219-T87

Abstract

Kurzfassung

References

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