Through-thickness heterogeneity in creep properties of friction stir welding 7B50-T7451 aluminum alloy thick plate joint: Experiments and modeling

Abstract

Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding (FSW) joints was investigated. Creep tests for three slices of the FSW joint were conducted at the temperature of 150–200 °C and applied stress of 60–225 MPa. The theta projection method was used to predict creep curves and minimum creep rate. The results show that the minimum creep rate increases and creep rupture life decreases with the increase of creep temperature and applied stress. Creep properties of the FSW joint deteriorate along the thickness direction from the top to the bottom. The threshold stress of all three slices of the FSW joint decreases with the increase of creep temperature and even disappears at 200 °C for the bottom slice. Creep activation energy approaches the activation energy of the lattice self-diffusion of aluminum. The value of true stress exponent for different slices is approximately equal to three. The predominant creep mechanism of the FSW joint is dislocation viscous glide by lattice self-diffusion. What is more, a constitutive model is established based on the theta method to accurately describe creep behavior of different slices of the FSW joint.