Microstructure, Tensile, and Corrosion Characteristics of Similar and Dissimilar Joints of FSW AA5086-H32 and AA6061-T6511 from Various Atmospheric Environments

Abstract

Corrosion behavior, tensile properties, and microstructure of similar and dissimilar Friction Stir Welded (FSW) butt-joints between AA5086 and AA6061 exposed to five atmospheric environments—acidic, rainforest, mild marine, harsh marine, and arid— for three exposure periods—6-month, 1-year, and 2-year—were investigated. Weight loss test via the ISO 8407:1991 (E) C.1.1, tensile test via the Instron-5500R testing machine, and microstructure characterization via the Scanning Electron Microscope (SEM) equipped with an Oxford Instrument energy dispersive X-Ray analyzer (EDXA) were conducted. Results show that AA5086 similar welds had best corrosion resistance in the most severe case, 2-year at acidic test site. Yield strength changes were insignificant over time and between test sites. AA5086 similar welds had the highest ultimate tensile strength (UTS), but also had the highest degradation; further investigation showed premature fractures. AA6061 similar welds and AA6061-AA5086 dissimilar welds shared same UTS with the latter being slightly lower. AA5086 similar welds had the highest elongation percentage. AA6061-AA5086 dissimilar weld samples exposed in the most severe test scenario exhibited marked changes in elemental composition and surface features at the parent material zone (PM), heat affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and nugget zone (NZ) when compared to an unexposed sample. The microstructure of 2-year samples exposed at the three most corrosive sites was also discussed. This study provides better understanding of similar and dissimilar FSW butt-joints of AA6061 and AA5086 for potentially greater application in shipping and aerospace industries.