Aging of medium strength aluminum alloy friction stir welds produced by different process parameter after tensile strain hardening Emanuela Cerri * , Paola Leo Dept. of Innovation Engineering, University of Salento, via per Arnesano, 73100 Lecce, Italy highlights  FSW joints have been investigated after tensile deformation and aging.  Tensile strain hardening induces a 20e25% HV increment in the stirred zone.  Subsequent aging at 200  C did not substantially modify hardness profiles.  After aging at 300  C, HV values were uniform and lower than HV minimum. article info Article history: Received 10 May 2013 Received in revised form 11 June 2014 Accepted 29 June 2014 Available online 14 July 2014 Keywords: A. Metals B. Welding C. Hardness D. Mechanical properties abstract Effect of tool rotation rate and travel speed on aging of 6082T6 friction stir welds after tensile strain hardening were investigated using Vickers microhardness (HV) measurements and precipitation hard- ening concepts. Tensile tests were performed at constant strain rate up to natural fracture followed by aging at low and medium temperatures. The results showed that HV measured on strain hardened FSW joints was not very sensitive to travel speeds experienced during FSW process, at constant rotation rate; anyway, strain hardening was very effective on hardness and induce an average increase by 20e25% in the stirred zone (SZ). Strain hardening was also very effective on aging at 200  C, while it was not at 300  C. At this temperature, HV assumed uniform values along joint cross section. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Many processing routes utilize severe plastic deformation to refine metallic material structures. The friction stir welding (FSW) technique is a potential and attractive joining technology that has been extensively applied on aluminum alloys. FSW is an effective means of refining grain size of cast or wrought aluminum or magnesium based alloys via dynamic recrystallization. In FSW, the work piece does not reach the melting point, and the mechanical properties such as ductility and strength of the welded zone are much higher compared with the traditional welding techniques [1]. The attractive mechanical properties are principally a result of the strong grain refining effect of the pro- cess. The data available in the literature suggest that the mean grain size resulting from the FSW process is at least ten times smaller than that measured in the undeformed parent material [2,3]. Thus, the results of these previous studies suggest that FSW can cause grain refinement through severe plastic defor- mation. In particular, a single pass of FSW produces an estimated effective strain >40 [4] resulting in a mean size of 0.5e10 mm. From this point of view, some authors have suggested that the microstructure in the weld zone evolves through a continuous dynamic recrystallization process. Actually, this is a core demand of aircraft and car industries to substitute the traditional joining technologies with low-cost and high-efficiency technologies such as FSW in the future advanced design. Recent literature re- ports examples of FSW of dissimilar aluminum alloys [5e7] as well as aluminum-steel [8e9], aluminumemagnesium [10] and aluminumesilver [11]. As the need for strong, lightweight, high corrosion resistance, high thermal and electrical conductivity, hot and warm formability materials has steadily been increasing, there has also been a growing interest in Aluminum Alloys which possess such proper- ties like that found in age-hardenable AleMgeSi alloy. The 6xxx- group of Aluminum Alloys (AA) contains magnesium and silicon as the major alloying elements. AleMgeSi alloys have recently been * Corresponding author. Present address: Dept. of Industrial Engineering, Uni- versity of Parma, v. G. Usberti 181/A, 43124 Parma, Italy. E-mail address: emanuela.cerri@unipr.it (E. Cerri). Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys http://dx.doi.org/10.1016/j.matchemphys.2014.06.068 0254-0584/© 2014 Elsevier B.V. All rights reserved. Materials Chemistry and Physics 147 (2014) 1123e1133