Microstructure Analysis of Friction Stir Welding of Aluminum Alloy 6061 Coated with Copper Nanofilm

This work presents the effect of various input process parameters on grain size of aluminum alloy 6061 coated with copper nanofilm in friction stir welding. In this experiment, copper nanofilm is coated with thermal evaporation unit on the sides of aluminum alloy plates. Copper film is deposited inside the vacuum chamber at a pressure of 4  10 – 4 Torr and a deposition rate of 4-6 Å per sec. The substrate temperature is maintained at 40 to 45 C. The distance between the boat and the substrate is maintained at 10 cm. Copper nanofilms with a thickness of 300, 600 and 900 nm are fabricated on various aluminum alloy plates. Friction stir welding machine is used to perform the butt welding on aluminum alloy 6061 coated with copper nanofilm with different thickness. Welding speed, tool rotational speed and copper nanofilm coating thickness are considered as input process parameters, and grain size viz. grain area and grain perimeter as output parameters. Based on three input parameters, each at three levels, nine experiments are carried out using Taguchi L9 orthogonal array approach. Regression model is also developed to predict the grain size of the microstructure. Grain size of these samples is noted by using image analysis software with inverted metallurgical microscope at 200X magnification. It is observed that copper nanofilm coating has a significant impact on the grain area and grain perimeter. By increasing the nanofilm thickness from 600 to 1800 nm, the mean grain area decreases by 20.83 m2 and simultaneously the mean grain perimeter decreases by 8.57 m. Also, the copper nanofilm coating has the maximum effect on the grain size, followed by welding speed and tool rotational speed. By increasing the welding speed from 30 to 60 mm/min, the grain perimeter decreases by 6.47 m, whereas the rotational speed has a mixed response.