A Numerical Simulation for Dissimilar Aluminum Alloys Joined by Friction Stir Welding

Dissimilar aluminum alloy sheets of 2017A-T451 and 7075-T651 were friction stir welded. A numerical simulation was developed to visualize the material flow and temperature distribution and to correlate the microstructure with hardness behavior. Due to the flow of surface material into the workpiece thickness, the weld nugget is composed of alternating layers of 7075 and 2017A. These layers have unique temperature histories depending on the material's initial position; therefore, they also have distinctive precipitate distributions. Supersaturated surface material flows into the process zone and forms a core in which GP zones re-precipitate upon cooling. Mid-plane and bottom-plane material flow toward the workpiece surface and encompass the surface material core. Within this region, the weld temperatures overage the equilibrium. phase in 2017A, decreasing the hardness, and at the same time dissolve the equilibrium eta/T phase in the 7075, leading to re-precipitation of GP zones upon cooling and a hardness recovery.