Effect of strain and dispersoids on abnormal grain growth, precipitation behavior and mechanical properties at longitudinal weld in Al-Li alloy profile

Abstract

The grains at the longitudinal weld in porthole extrusion profiles are more prone to abnormal growth during solid solution treatment, leading to a decline in mechanical properties. To improve the microstructure and enhance the mechanical properties at the longitudinal weld in profile, the precipitation behavior of the dispersoid in 2195 Al-Li alloy with different homogenization heating rates was studied. The impact of dispersoid morphology and distribution on grain structure and mechanical properties at the longitudinal weld was elucidated. The results indicated that the ramp heating homogenization treatment significantly promoted the precipitation of fine Al3Zr dispersoids, which effectively hindered the abnormal growth of grains within the low plastic deformation zone at the longitudinal weld and reduced the width of the coarse grain zone. The tensile strength and elongation of the ramp heating homogenized (RH) profiles after water quenching and aging were higher than those of the fast heating homogenized (FH) profiles. It was also found that the incoherent Al3Zr dispersoid within the recrystallized grains of the profile was prone to induce the precipitation of quench-induced phases. Due to the reduction of recrystallization fraction at the longitudinal weld in RH profile, the precipitation of quench-induced phases was inhibited. The strength of the air-quenched and aged RH profile was higher than that of the FH profile. It can be concluded that the extrusion process using the RH billet can improve the microstructure and mechanical properties at the longitudinal weld in 2195 Al-Li alloy profile.