Analysis of AA2XXX/AA7XXX friction stir welds

Large ranges of fabrication parameters are investigated in the present study to obtain dissimilar friction stir welded joints made of AA2139-T8 and AA7020-T651 aluminum alloys for the design of high-performance hybrid aeronautical structures. Detailed microstructural and mechanical characterizations of the various joints are conducted in order to determine the influence of the welding parameters on the microstructure and mechanical properties. Comparable microstructures and mechanical properties are interestingly obtained for the different joints welded in the range 600-1000 rev.min-1 / 250-550 mm.min-1 as rotation and advance speeds, respectively. Joints exhibit tensile properties as good as 77% to 79% of the yield strength and 88% to 96% of the ultimate tensile strength of the AA7020 base material. Except for the high speed conditions that failed in the nugget, all joint variants failed in the heat affected zone (HAZ), which also demonstrates lower hardness properties. In addition, a critical temperature range that produces a decrease of hardness is defined from temperature measurement in the HAZ. Such a combination of dissimilar alloys offers conservative mechanical properties for a large range of welding parameters suitable for the assembly purpose of high-performance structural components.