Influence of temperature cycles on the microstructures and mechanical properties of the partially melted zone in the fusion welded joints of 2219 aluminum alloy

The partially melted zone (PMZ) is a weakness region in the fusion welded joints of 2219 aluminum alloy due to the microsegregation of brittle eutectics (α(Al)+θ(Al2Cu)). The influence factors on the microstructures and mechanical properties of the PMZ in the joint have not been well understood. In this study, the microstructures of the PMZ were simulated using Gleeble thermal simulator with different temperature cycles. The microsegregation extents in the simulated PMZs were quantitatively analyzed through measuring the lattice parameters of α phase using X-ray diffraction technique. The mechanical properties of the PMZ were measured by the tensile test. It was found that the peak temperature of the temperature cycle was the main influence factor on the microstructures and mechanical properties of the PMZ. With the peak temperature increasing from 550 to 630 °C, the amount of the microsegregated eutectics increased, the concentration of the solutionized Cu in the α phase decreased, and the mechanical properties of the PMZ decreased. The mechanical properties of the PMZs with different temperature cycles showed that the PMZ was solid solution strengthened by Cu. The true stress of the tensile tested PMZ at various strain levels increased linearly with the Cu concentration in the α phase matrix. In order to explain the influence of temperature cycle on the microsegregation of PMZ, a semi-analytical model that takes into account both the melting process and solidification process of the PMZ was derived basing on the Clyne-Kurz׳s model. The predicted results of the model partially agreed with the experimental results.