Effect of additional cooling during friction stir welding on structure and properties of aluminum alloy joints

Abstract

The mechanical and corrosion properties of welded joints of sheets with a thickness of 5 mm made of the Al–Cu– Mg system alloy in the T state (hardening and natural ageing) and the 1565сhN116 alloy with a thickness of 3 mm, obtained by friction stir welding (FSW) in air and in water, are studied. It is established that additional cooling of the welded joint by water helps to increase the ultimate strength of the weld, slightly changing the properties of the welded joint. The destruction of the welded joint in both cases occurs along the thermo-mechanical affected zone. The strength of the welded joint of the Al–Cu–Mg system alloy and the 1565chN116 alloy is 0.8 and 0.95...0.99 of the strength of the base metal, respectively. When FSW of the Al–Cu–Mg system alloy in the T state in water, in comparison with welding in air, there is an increase in the microhardness of the mixing zone by 20 % and a decrease in the grain size in it from 9.8 to 4.8 μm. For the 1565chN116 alloy under the same conditions, an increase in the microhardness of the metal of the thermo-mechanical affected zone and the mixing zone by about 12 % and reduction of grain size in the mixing zone from 6 .8 to 4.5 μm is detected. At the same time, both for the Al–Cu–Mg system alloy in the T state and the 1565chN116 alloy during FSW in water, the length of the heat-affected zone decreases by about 1.6—2.2 times compared to FSW in air. For both alloys, an increase in the cooling rate during FSW leads to an increase in resistance against intercrystalline corrosion of all zones of the welded joint by about 1.5—2 times.