Corrosion Resistance Of Aluminium Alloy Thick Plate Friction Stir Welded Joints And The Effect Of Electron Beam Treatment

As an advanced solid phase bonding technology,Friction stir welding(FSW)was especially suitable for the low-melting light metals' welding.As the FSW joint's microstructures and stress conditions are different,it will show different corrosion behaviorIn this paper,the double-sided processes of friction stir welding were used on 6061 and 7075 aluminium alloy in the thickness of 30 mm,and the microstructure,microhardness and corrosion resistance along the thickness of the welded joints were studied.Electron beam surface modification technology was used to treat aluminium alloy FSW joints,and the corrosion resistance of the joints before and after electron beam treatment was compared.The main contents were as follows:The friction stir welding of 6061 and 7075 aluminium alloy thick plates were carried out by using the welding parameters with the stirring speed of 360r/min and the welding speed of 120mm/min,and got good shape of the welding samples.The FSW joint was divided into four zones: base metal zone,heat affected zone,thermal mechanical affected zone and weld nugget zone.There was an obvious boundary between the advancing side thermal mechanical affected zone and base metal in these two kinds of joints,the back boundary was blurred,the base metal was a typical rolled structure,the heat affected zone had undergone a slight coarsening,the grains of thermal mechanical affected zone was elongated and refined along the interface near the weld nugget zone,the grains in weld nugget zone were fine equiaxed crystal,the microstructure of the bottom weld nugget zone of the double-side welded was more uniform and fine equiaxed grains.The microhardness of 6061 and 7075 aluminium alloy FSW joints distributed as "W" shape,the microhardness of the upper part of the joint was higher than the bottom,the minimum of the microhardness appeared in the heat affected zone of advancing side,indicating that the heat affected zone of the advancing side was a weak link in the FSW joint.The electrochemical corrosion experiments were carried out on the joints,the corrosion current was larger in the overlapping zone of 6061 aluminium alloy double-side welded joint,once the corrosion was started,the corrosion speed was very fast,and the corrosion resistance was relatively poor,the corrosion resistance of the front side welding was slightly better than that of back side welding.Experimental result of corrosion of 7075 aluminium alloy thick plate FSW joint showed that the corrosion resistance of the base metal was the best,the weld nugget zone was the second,and the mixing zone,which including the weld nugget zone,the thermal mechanical zone and the heat affected zone was the worst,and the corrosion resistance of the front side welding was better than that of the back side welding.The electron beam pulse processing of the surface of 6061 and 7075 aluminium alloy FSW joints was carried out by electron beam surface modification technique.The electrochemical corrosion of the samples after the electron beam treatment were carried out,the results showed that the self-corrosion current density and self-corrosion rate of 6061 and 7075 aluminium alloy FSW joints decreased after pulse treatment.It can be seen that the electron beam pulse treatment had a positive effect on the long-term corrosion for the joints,the corrosion resistance of the joint can be improved effectively by electron beam pulse treatment...