Despite studies regarding mechanical and corrosion properties of Al 6061 alloyweldment, there is not sufficient information about fusion welding of nanostructured and bimodal (nano/micro) grained aluminum. The nonostructured material have attracted great interest due to their excellent physical and mechanical properties. Therefore, it is important to evaluate the mechanical and corrosion properties of their joints. Although nanocrystalline materials exhibit high strength, they display low ductility. One efficient approach to compensate this defect is to develop bimodal microstructures. For this purpose, in this resurch, samples were solution treated at 530 ?C for 3 hours and subsequently cryorolled up to 90% reduction in thickness. For obtaining simultaneous strength and ductility, the cryorolled alloy was then subjected to aging treatment at 130 ?C for 25 hours. A bimodal microstructure consist of nano-sized and micron-sized grains along with nano-sized (50-150 nm) stregthening precipittes was obtained after cryorolling and aging treatment. Transmission electron microscopy (TEM) was used for microstructural characterization of cryorolled samples. The average size of fine grains in aged sample was estimated about 60 nm. Improved ultimate tensile strength of 365 MPa, hardness of 140 HV, and ductility of 12 % was obtained for the produced aluminum sheets. The samples in as rolled (AR) and peak aged (PA) condition and also the 6061-T6 Al alloy sheets (witness samples) were then resistance spot welded with welding current of 40-100 kA, electrode force of 3 kN, and welding time of 0.1 s. Mechanial tests reaveld that the highest peak load of weld spot of nanostructured samples was about 5700 N, obtained through weldig current of 95 kA. All welded specimens failed in an interfacial fracture mode. At constant welding parameters microhardness of weld metal was similar for nanostructured samples and conventional grained samples owing to similar microstructure and grain size. According to the results of phase analysis of weld nugget, dissolution of Mg 2 Si precipitates in fusion zone occured during welding process which led to decrease of microhardness in this region. Similar corrosion behaviour of weld zone was observed for nanostructured and conventional grained samples in tafel polarization tests. For all specimens, corrosion potential of weld metal was lower than base metal due to dendritic microstructure of the weld metal. Keywords : Bimodal microstructure, Cryorolling, Resistance Spot Welding, Mechanical properties, Corrosion.
