Effect of solid solution treatment on the kinetics of hydrogen porosity evolution and mechanical properties in Al–Cu–Li alloys

Abstract

The evolution kinetics of hydrogen porosity during solid solution treatment (SST) of vacuum-cast Al–Cu–Li alloys and the effect of porosity defects on the mechanical properties of the alloys were investigated. It has been found that porosity at 6h SST was dominated by nucleation and its evoluton of fractions has a linear correlation with time, APS = (0.05 ± 0.06)＋(0.11 ± 0.01) t. However, the growth of porosity at 12 h is evidenced by a decrease in the number of pores and an increase in the size of large pores, expanding inter-porosity distance due to Ostwald ripening. Three dimensional quasi-in situ X-ray CT quantification of porosity demonstrate that the hydrogen concentration at the interface in the early stages of the solid solution was not adequate to balance its surface tension and vacancies were created by cross-diffusion, reducing the interficial energy for porosity nucleation. The effects of porosity on the tensile strength satisfies lnσ-lnσ0 = αlnfp, and those detrimental hydrogen porosities can be predicted by a multi-scale model which take into account hdyrogen diffusion during vacuum solution treatment.