ARKONIK SMZ, Samara, Russia:

A. M. Drits, Business Development Director, e-mail: alexander.drits@arconic.com

Moscow Polytechnic University, Moscow, Russia:
V. V. Ovchinnikov, Professor

SESPEL Cheboksary Enterprise, Cheboksary, Russia:
V. A. Bakshaev, General Director

The authors of this paper determined what parameters would be optimum for friction stir welding (FSW) of 28 mm thick plates made from AD0 aluminium grade. The findings suggest that, in the friction stir welding of AD0 aluminium plates, quality joints can be obtained through double welding (i.e. alternate face and root welding). A comparasion mechanical test was performed which looked at plate joints produced by friction stir welding and by multiple pass hand TIG welding with an SvA5 filler wire. The impact toughness of the joint metal was tested at room and low (–60 ^oC) temperatures. It was established that the strength of the FSW joint is more than 95% of the strength of the base material, and it was the heat affected area of the base material that broke in the specimens. In the case of hand TIG welding, the strength of the weld joint was 80–85% of the strength of the base metal, and it was the joint that broke. It is shown that the impact toughness in all cases is higher at –60 ^oC than at 20 ^oC, and the FSW joint has a higher absolute impact toughness than the base metal, whereas the absolute impact toughness of the fusion weld is lower that of the base metal. In the case of friction stir welding, mainly fine grains (5–6 μm), as well as a small amount of coarser grains (20–25 μm), were observed in the joint area and in the thermomechanical impact area. The heat-affected area can be characterized with an equiaxial recrystallized structure with the grain size of 50–60 μm. A typical onion-like structure can be observed in the metal structure of the weld joint. A more thorough observation reveals rings arranged in two levels. In between the level 1 rings one can observe rings of the other level, which can be described as a substructure. The layered structure is probably caused by a competition between strain hardening and softening caused by frictional heating and deformationinduced heat. This produces a metal layer with the same degree of deformation, while the yield strength at the boundary between this layer and the material it rests on is minimal, which leads to shear. This process keeps repeating itself, and this is how a layered structure is produced. Friction stir welding was successfully applied to produce a 15-6901 welded tank car with a boiler made of the 28 mm thick AD0 aluminium, as well as for welding of blank elliptic bottoms, which are also cold worked after welding.

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