Effect of temperature and friction on necking and thickening for 5A02 aluminum alloy thin-walled tube in differential temperature extrusion

Necking technology was widely used in the airplane pull rod parts. The tube end of airplane pull rod parts made by the traditional technology (such as spinning) was insufficient to thread directly, and it needed to rivet the threaded sleeve, which result in the low joint strength of airplane pull rod parts. Alternatively, a method of necking and thickening for a thin-walled tube using differential temperature extrusion was proposed for the purpose of threading directly. In this work, the effects of temperature and friction during the process of necking and thickening for 5A02 aluminum alloy thin-walled tube were conducted by finite element (FE) simulations and experiments. The simulation results showed that the higher the temperature was and the lower the friction coefficient was, the bigger the thickness of thickening area in the tube end was, which benefited to thread directly. Then, FE simulation was verified to be reliable by experiments. Subsequently, the effect of temperature on the microstructure in the thickening area of the formed workpiece was investigated by the optical microscopy. The microstructural morphology showed the grain size of the thickening area in the formed workpiece coarsened in comparison with the unformed tube when the material was heated at high temperature during the process of necking and thickening of tube. And the higher temperature was, the coarser the grain in the thickening area was. Finally, the reasonable forming temperature and friction was proposed for improving the micro and macro forming quality of the airplane pull rod parts under the necking and thickening process for thin-walled tube.