Uncovering the effects of local pressure and cooling rates on porosity formation in AA2060 Al-Li alloy

Abstract

The third generation of Al-Li alloys (e.g. AA2060) have been widely used in aerospace engineering. The formation of porosity during casting is a major obstacle for improving its mechanical properties due to the 10 times the equilibrium hydrogen concentration in the liquid than the traditional aluminum alloys. In this study, the effects of two fundamental parameters are investigated: cooling rate and pressure on the formation of porosity. The centrifugal casting process was used to apply external pressure during solidification and quantify the 3D porosity morphology as a function of the external parameters using X-ray computed tomography (X-CT). Subsequently, a Cellular Automata (CA) model was used to predict porosity as a function of pressure and thermal boundary conditions. It was found that the externally applied compressive pressure contributes to porosity closure within certain limits. In addition, the cooling rate not only refines the grain size but also minimizes porosity defects by increasing their number density, and the experimental results validated the predictions by the CA model. By increasing the solidification pressure and cooling rate, a high-performance AA2060 Al-Li alloy with a tensile strength of 490 MPa and an elongation of 6.1% was obtained.