International audienceFriction stir welding of dissimilar heat treatable 2139-T8 and 7020-T651 aluminum alloys was investigated in a large operating window of industrials welding parameters. Detailed microstructural and local mechanical characterizations have shown that despite consistency in the macroscopic tensile behavior of the different processed joints, local discrepancies in hardness highlighted the sensitivity of the two aluminum alloys to the welding process parameters. For this reason, a local characterization of the joint was undertaken. The local tensile behavior of the joints was investigated at the microstructure scale thanks to the use of an optical high-resolution digital image correlation (OHR-DIC) technique. The aim of this in-situ microtensile technique was to accurately calculate the local strain fields in the cross-weld section from kinematic field measurements. OHR-DIC micro-mechanical analysis demonstrated that strain localization first appears in the nugget region, then in the HAZ leading to fracture in this latter region. This study gives the opportunity to get an overall view of the welding parameters influence on the microstructural and mechanical characteristics of the welded joints and thus, make the right industrial choice according to the application. Keywords: FSWed dissimilar aluminum joint, Hybrid lightweight design, Digital image correlation, Tensile behavior Introduction Currently, reducing the weight of transport structure is an important challenge. The aluminum alloys (AA) 7020 comply with this constraint. AA7020 is a medium strength Al-Zn-Mg alloy well known for its good mechanical performance [1]. However, Al-Cu-Mg alloys, such as AA2139, will progressively replace 7XXX alloys because of the conjunction of higher mechanical strength and lower density [2]. Unfortunately, the intensive use of AA2139 is limited due to the production cost. Building hybrid structure by assembling medium-performance and high-performance aluminum alloys as a function of the local stresses in the structure is an attractive solution for cost-effective design strategies. In order to assemble these dissimilar alloys, Friction Stir Welding (FSW) is particularly suitable. Several process parameters, such as speeds [3], axial force [4], plates position [5], were reported to influence both the material flow of the weld and the mechanical behavior. In the present study, various dissimilar joints AA2139-T8/AA7020-T651 were produced with a large range of industrial welding parameters in order to correlate these parameters with the local mechanical behavior
