Microstructure characterization, mechanical properties, and corrosion behaviors of friction stir welded Aa5086 and Aa6061

Abstract

The objective of this research was to study microstructure characterization, mechanical properties, and corrosion behavior of friction stir welding AA5086 and AA6061. The microstructure of six distinct zones (NZ, TMAZ, HAZ, BM, downside, and cross-section) of friction stir welding AA5086-AA5086, AA5086-AA6061, and AA6061-AA6061 were investigated using etching technology and optical microscope. The hardness of friction stir welding AA5086-AA5086, AA5086-AA6061, and AA6061-AA6061 was measured by Wilson Rockwell Vickers Micro-hardness Tester to study how distinct regions affect mechanical properties. Tensile tests were conducted to study tensile and yield strength of friction stir welding AA5086-AA5086, AA5086-AA6061, and AA6061-AA6061. The results indicate that the fracture occurred in the relatively weaker TMAZ/HAZ. In this study, two major corrosion evaluation methods were used: the polarization test and the immersion test. Polarization experiments of critical regions of friction stir welding AA5086-AA5086, AA5086-AA6061, and AA6061-AA6061 were conducted in deaerated 3.15 wt% NaCl to study the governing corrosion mechanisms. Cathodic polarization of critical zones of friction stir welding AA5086-AA5086, AA5086-AA6061, and AA6061-AA6061 were conducted in aerated 3.15 wt% NaCl and 0.5 M Na2SO4 solutions. These results show that friction stir welding improves the corrosion resistance of AA5086 and AA6061 and that the HAZ and downside regions have better corrosion resistance than other regions. The immersion experiments were conducted to study corrosion properties of friction stir welding AA5086-AA5086, AA5086-AA6061, and AA6061-AA6061. Specimens of friction stir welding AA5086-AA5086, AA5086-AA6061, and AA6061-AA6061 were soaked in 3.15 wt% NaCl, 0.5 M Na2SO4 and American Society for Testing and Materials (ASTM) seawater for 90 days and 120 days at 30°C. The X-Ray Diffraction (XRD) and Raman spectroscopy were used to characterize the immersion samples and revealed that aluminum hydroxide was the main corrosion product. Intergranular attack was observed in the NZ and downside by scanning electron microscopy (SEM).