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.

本研究针对AA2139-T8与AA7020-T651铝合金异种搅拌摩擦焊接接头，系统探究了大范围的焊接工艺参数，旨在为高性能混合航空结构的设计提供支撑。为明确焊接参数对接头显微组织与力学性能的影响规律，本研究对各类接头开展了细致的显微组织与力学性能表征工作。值得注意的是，当焊接转速区间为600~1000 r·min⁻¹、前进速度区间为250~550 mm·min⁻¹时，所制备的不同接头可获得相近的显微组织与力学性能。接头的拉伸性能可达AA7020母材屈服强度的77%~79%、抗拉强度的88%~96%。除高速工艺条件下接头于焊核处失效外，其余所有接头试样均在热影响区（heat affected zone，HAZ）发生断裂，该区域同样表现出更低的硬度特性。此外，通过对热影响区的温度检测，本研究明确了导致硬度下降的临界温度区间。此种异种铝合金组合在宽泛的焊接参数范围内均可展现出满足应用需求的稳健力学性能，适用于高性能结构构件的装配制造。