Abstract
AA7075-T651 plates were friction stir welded using in-process cooling with the intention of investigating variations in microstructure and hardness across the joint in through thickness direction. The variations were studied using optical microscopy, transmission electron microscopy (TEM) and hardness tests. Water cooled welds exhibit better performance in terms of hardness compared to air cooled welds. However, both welds were found to display considerable reduction in the hardness in the heat-affected zone (HAZ). Furthermore, hardness across the joint enhances as the survey proceeds away from the surface of the specimen to the root of the weld. The weld nuggets in both welds reveal fine recrystallized grains and the grain size was found to dwindle from surface to root of the joint along the thickness of the weld. TEM studies disclose that the weld nugget suffers from dissolution of precipitates and the HAZ consists of precipitate-free zones, which are considered accountable for lower hardness in the HAZ. It is concluded that defect-free welds can be made with thick plates of AA7075-T651 using in-process cooling and furthermore, water cooled welds exhibit better hardness values.
Kurzfassung
Für den vorliegenden Beitrag wurden Bleche der Aluminiumlegierung 7075-T651 rührreibgeschweißt, wobei diese aus dem Prozess heraus unterschiedlich abgekühlt wurden und zwar mit der Intention, die Veränderungen der Mikrostruktur und der Härte in Dickenrichtung zu untersuchen. Die Veränderungen wurden mittels Lichtmikroskopie, Transmissionselektronenmikroskopie (TEM) und Härtetests untersucht. Schweißungen, die in Wasser abgekühlt wurden, zeigten bessere Härtewerte als diejenigen, die an Luft abgekühlt wurden. Dennoch stellte sich heraus, dass beide Schweißungen eine beachtliche Reduktion der Härte in der Wärmeeinflusszone (WEZ) aufwiesen. Darüber hinaus verbesserte sich die Härte mit größerer Entfernung von der Oberfläche in Richtung der Wurzel der Schweißungen. Beide Schweißungen wiesen feine rekristallisierte Körner auf und es stellte sich heraus, dass die Korngröße von der Oberfläche zur Wurzel über die Dicke der Schweißungen abnahm. Mit den TEM-Studien ließ sich nachweisen, dass die Schweißungen eine Auflösung der Ausscheidungen erfuhren und dass die WEZ aus einer ausscheidungsfreien Zone bestand, was sich bezüglich einer niedrigeren Härte in der WEZ als vorteilhaft erwies. Außerdem zeigte sich, dass defektfreie Schweißungen von dicken Blechen der Aluminiumlegierung AA7075-T651 erzeugt werden können, indem die Abkühlung direkt aus dem Prozess heraus vorgenommen wird, und dass die wassergekühlten Schweißungen bessere Härtewerte aufweisen.
References
1 M.Kleiner, M.Geiger, A.Klaus: Manufacturing of lightweight components by metal forming, CIRP52 (2003), pp. 521–54210.1016/S0007-8506(07)60202-9Search in Google Scholar
2 N. N.: Metals Handbook, 9th Edition, ASM, Metals Park, Ohio, USA, Vol. 6 (1983)Search in Google Scholar
3 J. Q.Sua, T. W.Nelson, C. J.Sterling: Microstructure evolution during FSW/FSP of high strength aluminum alloys, Materials Science and Engineering A405 (2005), pp. 277–28610.1016/j.msea.2005.06.009Search in Google Scholar
4 H.Fujii, L.Cui, M.Maeda, K.Nogi: Effect of tool shape on mechanical properties and microstructure of friction stir welded aluminum alloys, Materials Science and Engineering A419 (2006), pp. 25–3110.1016/j.msea.2005.11.045Search in Google Scholar
5 Y.Chena, H.Liu, J.Feng: Friction stir welding characteristics of different heat-treated-state 2219 aluminum alloy plates, Materials Science and Engineering A420 (2006), pp. 21–2510.1016/j.msea.2006.01.029Search in Google Scholar
6 P.Cavaliere, G.Campanile, F.Panella, A.Squillace: Effect of welding parameters on mechanical and microstructural properties of AA6056 joints produced by friction stir welding, Journal of Materials Processing Technology180 (2006), pp. 263–27010.1016/j.jmatprotec.2006.06.015Search in Google Scholar
7 H. B.Chen, K.Yan, T.Lin, S. B.Chen, C. Y.Jiang, Y.Zhao: The investigation of typical welding defects for 5456 aluminum alloy friction stir welds, Materials Science and Engineering A433 (2006), pp. 64–6910.1016/j.msea.2006.06.056Search in Google Scholar
8 R. S.Mishra, Z. Y.Ma: Friction stir welding and processing, Materials Science and Engineering R50 (2005), pp. 1–7810.1016/j.mser.2005.07.001Search in Google Scholar
9 W. M.Thomas, E. D.Nicholas, J. C.Needham, M. G.Murch, P.Temple-Smith, C. J.Dawes: Friction Stir Butt Welding: GB Patent, 9125978.8, 06-12-1991Search in Google Scholar
10 K. A. A.Hassan, P. B.Prangnell, A. F.Norman, D. A.Price, S. W.Williams: Effect of welding parameters on nugget zone microstructure and properties in high strength aluminum alloy friction stir welds, Science and Technology of Welding and Joining8 (2003), pp. 257–26810.1179/136217103225005480Search in Google Scholar
11 J. Q.Sua, T. W.Nelson, R.Mishra, M.Mahoney: Microstructural investigation of friction stir welded 7050-T651 aluminium, Acta Materialia51 (2003), pp. 713–72910.1016/S1359-6454(02)00449-4Search in Google Scholar
12 C. G.Rhodes, M. W.Mahoney, W. H.Bingel, R. A.Spurling, C. C.Bampton: Effects of friction stir welding on microstructure of 7075 aluminum, Scripta Materialia36 (1997), pp. 69–7510.1016/S1359-6462(96)00344-2Search in Google Scholar
13 K. V.Jata, K. K.Sankaran, J. J.Ruschau: Friction-stir welding effects on microstructure and fatigue of aluminum alloy 7050-T7451, Metallurgical and Materials Transactions A31A (2000), pp. 2181–219210.1007/s11661-000-0136-9Search in Google Scholar
14 M. W.Mahoney, C. G.Rhodes, J. G.Flintoff, R. A.Spurling, W. H.Bingel: Properties of friction-stir-welded 7075 T651 aluminum, Metallurgical and Materials Transactions A29A (1998), pp. 1955–196410.1007/s11661-998-0021-5Search in Google Scholar
15 M.Peel, A.Steuwer, M.Preuss, P. J.Withers: Microstructure, mechanical properties and residual stresses as a function of welding speed in aluminum AA5083 friction stir welds, Acta Materialia51 (2003), pp. 4791–480110.1016/S1359-6454(03)00319-7Search in Google Scholar
16 H. J.Liu, H.Fujii, M.Maeda, K.Nogi: Tensile properties and fracture locations of friction-stir-welded joints of 2017–T351 aluminum alloy, Journal of Materials Processing Technology142 (2003), pp. 692–69610.1016/S0924-0136(03)00806-9Search in Google Scholar
17 K. A. A.Hassan, A. F.Norman, D. A.Price, P. B.Prangnell: Stability of nugget zone grain structures in high strength Al alloy friction stir welds during solution treatment, Acta Materialia51 (2003), pp. 1923–193610.1016/S1359-6454(02)00598-0Search in Google Scholar
18 T. SrinivasaRao, G. MadhusudhanReddy, S. R. KoteswaraRao: Microstructure and mechanical properties of friction stir welded AA7075–T651 aluminum alloy thick plates, Transactions of Nonferrous Metals Society of China25 (2015), pp. 1170–117810.1016/S1003-6326(15)63782-7Search in Google Scholar
19 T. SrinivasaRao, G. MadhusudhanReddy, G. SrinivasaRao, S. R. KoteswaraRao: Studies on salt fog corrosion behavior of friction stir welded AA7075–T651 aluminum alloy, International Journal of Materials Research105 (2014), pp. 375–38510.3139/146.111033Search in Google Scholar
20 S.Benavides, Y.Li, L. E.Murr, D.Brown, J. C.McClure: Low-temperature friction-stir welding of 2024 aluminum, Scripta Materialia41 (1999), pp. 809–81510.1016/S1359-6462(99)00226-2Search in Google Scholar
21 J. Q.Su, T. W.Nelson, C. J.Sterling: A new route to bulk nanocrystalline materials, Journal of Materials Research18 (2003), No. 8, pp. 1757–176010.1557/JMR.2003.0243Search in Google Scholar
22 T. W.Nelson, R. J.Steel, W. J.Arbegast: In situ thermal studies and post-weld mechanical properties of friction stir welds in age hardenable aluminium alloys, Science and Technology of Welding and Joining8 (2003), No. 4, pp. 283–28810.1179/136217103225011005Search in Google Scholar
23 T. SrinivasaRao, G. MadhusudhanReddy, S. R. KoteswaraRao: Studies on variations in microstructure and hardness of AA7075-T651 aluminum alloy friction stir welds, La Metallurgia Italiana1 (2016), pp. 29–35Search in Google Scholar
24 S.Rajkumar, C.Muralidharan, V.Balasubramanian: Influence of friction stir welding process and tool parameters on strength properties of AA7075–T6 aluminum alloys joints, Materials and Design32 (2011), pp. 535–54910.1016/j.matdes.2010.08.025Search in Google Scholar
25 J. A.Wert: Identification of precipitates in 7075 Al after high-temperature aging, Scripta Materialia15 (1981), pp. 445–44710.1016/0036-9748(81)90228-3Search in Google Scholar
26 G. W.Lorimer: Precipitation in aluminum alloys, K. C.Russell, H. I.Aaronson (Eds.): Precipitation Processes in Solids, Metallurgical Society of AIME, Warrendale, PA, USA (1978), pp. 87–119Search in Google Scholar
© 2017, Carl Hanser Verlag, München
