| Cu-Cr-Zr alloy with excellent strength and conductivity performance, has become the preferred material for motor rotor bar and end ring for a new generation of ship. Currently, the weld of Cu-Cr-Zr alloy prone pores, not welded together and cracks, also a serious decline of mechanical and electrical properties by the conventional welding methods. Based on the superiorities of the friction stir welding (FSW) technology, this paper studied the friction stir welding process of Cu-Cr-Zr alloy and post weld heat treatment for improving the performance of the weld.Firstly, a three dimensional Cu-Cr-Zr alloy FSW steady heat transfer finite element model is simulated by ANSYS13.0. The simulation results showed that high temperature zone was distributed around the stir tool and the maximum temperature reached1220K. The temperature of advancing side was observed to be higher than that retreating side, also,the behind of the tools higher than the ahead. Compared with the model of water cooling process of FSW, the results showed that adding water cooling can effectively control the welding temperature and reduce the high-temperature zone, thus achieved the purpose to reduce the high-temperature’s effect of softening to the weld and base material.Secondly, the water cooling process of FSW carried on Cu-Cr-Zr alloy, and the microstructure and properties of welds are analysised. The results show that the properties of joints declined seriously:the tensile strength was264.3MPa which was59%of the base metals, the yield strength was130.45MPa which was only59%of the base metals, the hardness was71HV, only50%of the parent material; the electrical conductivity was40%IACS which reduces to67%of the parent material. Under the high welding temperature, a large number of strengthened precipitated phases disappear and solution back to the Cu matrix, which leads to the welded joints performance fell sharply.Lastly, the post welding heat treatment of Cu-Cr-Zr alloy friction-stir-welded joints at five groups of temperature, they are425℃, 450℃,475℃,500℃and525℃, respectively. The results indicate that the best post welding heat treatment of temperature is475℃. After heat treatment, the properties of Cu-Cr-Zr alloy friction-stir-welded joints are increased greatly:the tensile strength can reach to3O3.8MPa, an increase of15%, the yield strength is190.55MPa, an increase of46%, the micro-hardness can reach to110-120HV, an increase of70%, the conductivity from the mean value of40%IACS increased to60-70%IACS. In the matrix, the dispersion and distribution of precipitation phases precipitated from the supersaturated solid solution, can effectively improve organizational performance. To sum up, the post welding heat treatment can substantially improved the properties of Cu-Cr-Zr alloy friction-stir-welded joints. So the friction stir welding of Cu-Cr-Zr alloy and post welding heat treatment are feasible and effective, which can play an important role to develop a reasonable guiding for the ship motor rotor welding process. |
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