| Magnesium alloy is a green engineering material,which is of great significance for lightweight application in automotive field,3C electronics industry and aerospace field.Magnesium alloy Mg-4.5Al-1.2Sn-0.7Zn(ATZ511)is a magnesium-aluminium-zinc alloy with the addition of tin,manganese and other elements,which can improve the structure of the alloy and achieve the effect of grain refinement,thus increasing the strength and plasticity as well as the corrosion resistance.This series of magnesium alloys is still in the research and development stage,and has broad application prospects in the future industry.Therefore,the process,microstructure and properties of friction stir welding of ATZ511 magnesium alloy have been studied in this paper.In this paper,based on ABAQUS software and ALE model,a thermo-mechanical coupling three-dimensional model of the whole friction stir welding process is established,and the reliability of the model is verified by comparing with the test.It is found that the high temperature zone of plate appears in and around the stirring holes during friction stir welding,and the temperature field distribution is not symmetrical.The temperature in front of the stirring head is lower than that in back,but the temperature change is greater than that in back.By comparing the simulated and actual temperature change curves at 4 mm away from the weld,it is found that although there is a temperature difference,the temperature change trend is consistent and the model is basically accurate.A series of tests were carried out on ATZ511 magnesium alloy,including: Friction stir welding process exploration test,temperature measurement test,metallographic test,hardness test,mechanical tensile test.It is found that when the welding speed is constant at 75 mm / min,a good weld surface can be formed within the research range.The grain size formed at 1000-1500 rpm is small,and with the increase of the welding speed,the maximum welding temperature first rises and then tends to be stable;when the welding speed is constant at 1500 rpm,the low welding speed will produce serious flash,and for the microstructure,with the increase of the welding speed,the grain size gradually shrinks,and under different welding speeds the results show that the welding speed has little effect on the temperature of the whole welding process in a certain range,and the material can be plasticized.The microhardness curve of the joint presents "W" shape,and the hardness peak appears in the weld center.Two hardness valleys appear on both sides with the increase of the distance from the weld center,and then the hardness increases to the base metal level.When the rotation speed is constant at 1500 rpm,the higher the welding speed is,the higher the hardness peak value of the weld center is.When the welding speed is constant at75 mm / min,the hardness decreases with the increase of welding speed.For the mechanical properties of the joint,the maximum tensile strength and elongation of the joint are less than that of the base metal,but the decrease is not much,which can reach more than 90% of the base metal.The fracture position is at the base plane which is 45 ° to the tensile direction.Fracture morphology belongs to brittle fracture. |
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