Effect Of Temperature Field On Weld Formation And Joint Microstructure Of 5A06 Aluminum Alloy In FSW

Friction Stir Welding(FSW)is a new method of solid-state welding technology,which can effectively solve the problem such as heat crack,softening of the HAZ and transformation in the traditional melting welding,and provides a new method for the welding of aluminum alloy and other low-melting metal.The process of FSW is complicated,the temperature distribution of the joint can directly reflected by simulation of the welding temperature field,which will give guidance to learning welding mechanism,optimizing the welding parameters and avoiding joint defects.The heat input model of 5A06 aluminum alloy FSW process is established in this paper.The temperature field under different process parameters was simulated by using finite element analysis software ANSYS.The distribution of temperature field and the effect of rotating speed and welding speed on temperature field were researched during FSW;Compared with the result of thermal cycle in the welding process measured by the experimental method,the model was proved to be accurate;Weld surface formation,internal defects and microstructure of nugget zone were observed by using OM;the hardness of the joint cross-section was measured by hardness tester.The conclusions are as follows:The simulation result of temperature field shows that the temperature of the weld center is lower than the edge of shoulder,and the peak temperature decreases with the distance from the weld center increases,the temperature field is symmetrical on both sides of the weld.The rotational speed affects the peak temperature,but the welding speed affects residence time at the peak temperature,the rotational speed raise makes the highest temperature increases,the increase in welding speed tends to reduce the residence time at the highest temperature.The comparison between the experimental and the simulation results shows that the heat source model established in this paper can accurately simulate the distribution of temperature field during welding process.For 5A06 aluminum alloy with 12 mm thickness,the optimum welding parameters are ? = 220 r / min,v = 8 cm / min,the peak temperature of the weld reaches 377°C,the softening degree and the fluidity of the material is good,the weld without defect and with good surface morphology can be obtained.The hardness of 5A06 aluminum alloy joint is related to the grain size in it,the dynamic recrystallization occurred in the nugget zone which was transformed into a uniform fine equiaxed crystal,the hardness of this zone is reaches 84 HV which is about 15% higher than that of the base metal.The hardness of the weld cross section showed "n" type distribution,the grain size and hardness are not changed obviously in the thickness direction of the weld.The rotational speed increased tends to the decrease of grain growth tendency and hardness of the nugget zone,the welding speed has little effect on grain size and hardness.