Structure And Properties Of Friction Welding Of 6063-T6 Aluminum Alloy

Friction welding as a kind of solid phase connection technology,with its high quality,high efficiency,precision and the characteristics of energy saving,widely used in the fields such as aerospace,nuclear industry,ocean development and rail transportation,automobile manufacturing,oil drilling and machinery manufacturing industry sector,in the welding of aluminum and its alloy showed a huge advantage.For the connection of conductive aluminum alloy,it is necessary to consider both the strength and the conductivity,and the friction welding has a great advantage in the connection of conductive aluminum alloy.In this paper,the conductive aluminum 6063-T6 aluminum alloy was welded by using the rotating frictional welding,and the influence of friction pressure,friction time and pressure on welded joint properties were analyzed.The test results show that the nugget zone of the 6063-T6 aluminum alloy rotating friction welding is fine equiaxed grain.Secondary growth of grain in that heat affected zone was observed.The change of grain size in the thermo-mechanically affected zone is obvious,and the elongated grains formed by the large plastic deformation are clearly visible.When the friction pressure is kept between 40-60MPa,the friction time is 5-7s,and the top forging pressure is 60-90MPa,the welding joint with good surface forming and uniform flying edge can be obtained.TEM observation results show that equilibrium phase β phase and Si can be observed in the nugget zone when the heat input is low,no β",β’ precipitate phase.This means that the original strength phase in nugget zone is transformed equilibrium phase.With the increasing of friction heat,the β phase in the nugget zone resolves into the aluminum matrix again and form a saturated solid solution.Fine equiaxial crystals are formed by dynamic recrystallization in the nugget zone.The main strengthening phase of 6063 aluminum alloy is basically disappeared.The main strengthening method is fine grain strengthening,solid solution strengthening,and so on.The grain size is mainly affected by the friction pressure and time.The fracture position of the welded joint occurred at the lowest hardness of the thermal influence zone,and the welding joint had a sharp necking at the fracture position.The fracture of the welded joint was relatively flat,which was a mixed fracture with the main fracture of ductile fracture.When the upset forging pressure is 90MPa,the friction pressure is 60MPa and the friction time is 7s,the strength of joint is 165.7MPa and up to 74.4%of the base material.The electrical conductivity of welded joint is superior to that of the base material,because the precipitation of solid solution elements,which reduces the influence of lattice distortion on electron scattering,and improves the conductive performance of the joint.When the forging pressure is 120MPa,friction pressure of 60MPa,and the friction time of 7s,the welding joint with the highest electrical conductivity was obtained,and the conductivity was 50.64%IACS.The hardness is lowest near the heat affected zone.The hardness of the nugget zone is higher but still lower than that of the base material.The corrosion resistance test showed that in the 3.5%NaCl solution at room temperature and free oxygen,there was no passivation in the nugget zone.The corrosion resistance of welding joint with 30MPa friction pressure is the best compared with other friction pressure.The corrosion resistance of samples with different friction time is 5S is the best and 7S is the worst.The welding joint with 120MP has the best corrosion resistance than that of different forging pressure.