Properties and structure of joints of alloy 1151 of the Al – Cu – Mg system, obtained by friction stir welding with forced cooling of the seam

Abstract

The mechanical and corrosion properties of butt welded joints of 5 mm thick sheets of alloy 1151 of the Al – Cu – Mg system in the T temper (Hardening and natural aging) obtained by friction stir welding in air and under water are studied. It is established that forced cooling of the welded joint with water helps to increase the strength of the weld, slightly changing the properties of the welded joint. The destruction of the welded joint in both cases occurs along the thermomechanical influence zone (ZTMV). The strength of the welded joint is 0.8 of the strength of the base metal. When friction stir welding with stirring under water, in comparison with welding in air in the mixing zone, an increase in microhardness by 20% and a decrease in grain size from 9.8 to 4.8 microns are observed. Friction stir welding with stirring under water halves the length of the heat affected zone and does not affect the grain size in this zone. Intergranular corrosion of the base metal is 0.05 mm and is the lowest of all structural zones of the butt joint. When welding in air, the zone of thermal influence (HAZ) is most susceptible to intergranular corrosion — 0.35 mm. To a slightly lesser extent, intergranular corrosion is manifested in the zone of thermomechanical action (0.28 mm). After the base metal, weld metal (ZP) of 0.18 mm has the greatest resistance to intergranular corrosion. Due to the higher cooling rate during forced cooling in water, the resistance to intergranular corrosion of all zones of the welded joint (except the base metal) decreases by about 1.4–2 times depending on the structural zone. The greatest decrease in corrosion resistance to intergranular corrosion is observed for the thermomechanical impact zone (0.14 mm instead of 0.28 mm).