Friction Stir Welding of Aluminum 7075 Alloys

Abstract

Abstract: Friction Stir Welding (FSW) is a solid-state welding method which was developed by The Welding Institute and patented in 1999. The process is solid state and relies on local forging of weld region to perform weld. New welding schedules are being continuously developed for materials that are traditionally difficult to join by fusion welding methods (e.g., TIG/MIG). These experiments are performed to find out the best possible parameters to smoothly weld the aluminium 7075 alloys. By using Taguchi robust design of experiment, we selected 3 parameters namely rotation speed and transverse speed and tool shoulder diameter against the optimization function of ultimate tensile strength. The tilt angle and the plunge depth are kept constant. The variation of tensile strength is mainly due to the change in tool shoulder diameter then with welding speed and then with rotation speed. The heat generated is modelled on ANSYS software by inserting the rotation speed, coefficient of friction , material properties , radius of pin etc. The model is validated by conducting the experiment through thermocouples. The model predicted a temperature of about 410 degrees Celsius and the experimental value is 380 degrees Celsius, showing that the welding temperature is about 80% of heat generation. The Taguchi experiment consist of 4 experiments with a range of rotation speeds of 900 and 1120 respectively and a welding speed of 64mm/min and 100 mm/min respectively. The tool shoulder diameter is kept 14mm and 17mm. the welds are cut in transverse direction in order to obtain the UTS test coupon. The best possible combination is found using Taguchi Analysis. This thesis is a collection of data and response variables that correctly informs at what conditions we should weld 7075 alloy. Appropriate SN ratio is calculated and high is the best is considered as our objective function is tensile strength. Some additional tests are also performed namely hardness and microstructure and heat generation in order to identify the behaviors of aluminium alloy. Hardness and heat generated are dependent on the tool shoulder diameter then on the welding speed. This conclusion is derived from Taguchi analysis. This study is useful for the selection of parameters for the further welding operations. However, a change in plunge depth can also be taken into consideration for future scope. As tunneling defect was observed in some runs thus plunge depth has to be varied. Also, the number of experiments can be increased in order to get more refined parameters. Also, the making of base material can also be taken into consideration because of the zinc precipitate distribution. Casted AA7075 has different properties, rolled AA 7075 can have different.