EFFECT OF FRICTION STIR WELDING PARAMETERS ON MICROSTRUCTURAL CHARACTERISTICS AND CORROSION BEHAVIOR OF AA7020-O BASED ON TAGUCHI DOE APPROACH

In the present study, Taguchi approach for experiment design was utilized, through an orthogonal array of L₉ (3³), to investigate the effect of friction stir welding (FSW) process parameters, and post weld heat treatment (PWHT) on the microstructural characteristics and corrosion behavior of the nugget zone (NZ) of the FS welded joints and the base metal (BM) samples of AA7020-O. Microstructural characteristics were investigated through grains size (GS) and aspect ratio (AR) of α-Al grains. Corrosion behavior was studied by potentiodynamic              polarization test and static immersion in 3.5 % NaCl solution at room temperature. Results of analysis of variance (ANOVA) revealed that, the GS at center of the NZ is directly statistically significant affected by increasing the tool rotational speed and by changing the PWHT state from the as weld (AW) state to T4 or T6 tempers, while, the AS is directly statistically significant affected by increasing the tool rotational speed, and, it is inversely statistically significant affected by increasing the welding speed. Moreover, the corrosion rate (CR) is found to be directly statistically significant affected by changing the PWHT state from the AW state to T4 or T6 tempers, while, it is inversely statistically significant affected by increasing the tool rotational speed. Nevertheless, As compared to BM samples, FSW has highly decreased the CR in the NZ, for T4 and T6 tempers, while it is of comparable values in AW state. The percentage contribution (P_C) of each factor is also determined.
Key words: FSW, Processing Parameters, PWHT, Taguchi, Microstructure, Corrosion Behavior, Potentiodynamic Polarization, Corrosion Rate.