Pan Qinglin

Microstructure and Properties of Friction Stir Welded Joints of Al-Mg-Sc Alloy Plates

Abstract The hot rolled and cold rolled-annealed plates of Al-Mg-Sc alloys were welded by friction stir welding. The hardness distribution and the tensile properties of welded joints were measured; the relationships between the microstructure and the properties of the welded joints were studied by means of optical microscopy and transmission electron microscopy. The results show that the welding coefficients of two plates are as high as 92%, the hardness and strength of their weld nugget zones are the lowest, and the fracture of their welded joints happens at weld nugget zones during tensile testing. The decrease of the substructure strengthening caused by the partial recrystallization and the loss of precipitation strengthening from Al3(Sc, Zr) particles result in the decline of hardness and strength of Al-Mg-Sc alloy welded joints.

Research on the Hot Deformation Behavior and Processing Map of 2124 Aluminum Alloy Hot-Rolled Sheet

The hot deformation behavior of 2124 aluminum alloy hot-rolled sheet was investigated by means of hot compression test using Gleeble thermal simulation machine within the temperature range of 340-500° and strain rate range of 0.01-10s-1 with the maximum deformation degree set to 60%. The microstructure evolution during hot deformation was observed by optical microscope and transmission electron microscope. And its processing map was constructed based on dynamic material model to evaluate the optimum hot processing conditions and reveal the instability regions. The results showed the hot deformation activation energy is 170.13kJ/mol, and the softening mechanism of this alloy transform from dynamic recovery into dynamic recrystallization with the increase of deformation temperature or decrease of strain rate. The optimum processing parameters for the studied alloy is with deformation temperature at 460~480°C and strain rate of 0.01 ~ 0.1 s-1.