| Increasing with people's demand for intelligent life,the research and development of robotics technology have been further developed.Lightweight aluminum-based alloys have great advantages as material choices of making robots,but there is an urgent need to improve their performance and quality.Therefore,the use of directional solidification process to prepare high-performance aluminum alloy castings for the optimization of the robot material is of great significance.In the course of directional solidification,the research group adopted the Bridgman type vacuum furnace and liquid metal cooling method(LMC)under different temperatures(700?,750? and 800?)and pulling speeds(20?m/s,50?m/s,100?m/s and 150?m/s)to conduct directional solidification experiments.6061 aluminum alloys are selected as the experimental material.The castings were tested by universal tensile tester and microhardness tester respectively.The microstructure was observed by scanning electron microscope.The effect of vacuum directional solidification parameters on the mechanical properties and microstructure of 6061 aluminum alloy was studied.The change of the temperature field can not be observed in the experiment.Therefore,Pro CAST software is used to simulate the temperature field of the directional solidification process,and the influence of the directional solidification process parameters on the forming quality of the castings is studied.Through the experimental research and numerical analysis,the following conclusions are concluded:(1)When the pulling speed is constant and the drawing temperature is different,the tensile strength and the total elongation of the casting increase first and then decrease slightly,the highest tensile strength is at the temperature of 750?,reached 182.51 MPa and the total elongation at break reached 33.68%.The microhardness of castings showed an overall upward trend with the increase of temperature,reaching the maximum of 56.77 HV at the drawing temperature of 800?.Observation of their microstructure can be found that as the drawing temperature increases,the casting of the grain gradually increased and the grain spacing decreases,the mechanical properties increased.However,when the temperature is extended to 800?,defects such as cracks in the castings cause a slight decrease in the tensile properties of the castings.(2)When the drawing temperatures are constant and the pulling speeds are different,the tensile strength of the casting is the best at the drawing speed of 50?m/s,up to 183.31 MPa.While the pulling speed is 150?m/s,the casting hardness is highest,reaching 67.66 HV.From the microscopic point of view,as the pulling speed increases,the grains gradually increase and the grain spacing decreases,for the reason of improving the mechanical properties.With the increase of the pulling speed,some compounds are too late to be cooled and surrounded by the solidified alloy structure.The degenerated heat can not fuse the dendrites around the part,resulting in a small number of defects and leading to the decrease of the mechanical properties.(3)Based on the numerical simulation of the process of remelting and solidification,the changes of temperature field and solidification process were analyzed.The influence of process parameters on the microstructure of directional solidification was also studied.When the drawing temperature is 750?,the solidification of castings is the best.If the temperature is too high or too low,the grain growth will be slow,unstable and the spacing of the grains will be too large.The higher the stretching temperature is,the more the shrinkage is formed and the stronger the tendency of shrinkage is.The defects of the castings in the experiment illustrate the practicability of numerical simulation in the casting process of aluminum-based alloys.Increasing with pulling speeds,the grains are getting finer and the grain spacing is more and more closer.And the growth rates of dendrite firstly increase with the increase of pulling speeds and then decrease. |
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