Fatigue analysis of the friction stir welded AA6061-T6 aluminum alloy

Abstract

Investigation of mechanical and fatigue behavior is necessary to find out the long-term durability of the welded joints. The current work focuses on the mechanical and fatigue behavior of the joint formed when AA6061-T6 alloy plates were friction stir welded (FSWed) then joint was also analyzed as compared with parent material. The tensile strength and microhardness profile were obtained by the uniaxial tensile test and Vickers hardness test respectively. The maximum yield strength and ultimate tensile strength of the FSWed specimens were found to be 207.2 N mm−2 and 264 N mm−2 which are 72.2% and 80.3% of the parent metal respectively. The minimum value of hardness in FSWed specimen was equivalent to 63% of the parent material. The fatigue tests were carried out in a constant amplitude loading condition at a positive load ratio (R = 0.1). The limit of maximum stress applied during the fatigue tests was determined based on the results of the tensile tests. Microstructural and scanning electron microscope (SEM) examination of welded specimens was also carried out to understand the effect of FSW on microstructural development, commence of fatigue crack, and the way the crack spreads. The outcomes show the formation of a fine-grained microstructure in the center of the weldment. Results of the fatigue tests show that the fatigue strength of both types of configurations i.e. FSWed and parent material were almost the same at the low-stress level. At high-stress level, parent material exhibits superior fatigue strength than FSWed specimens. An effort has also been made to relate the fatigue resistance to the microstructural observations of the welded specimens.