Quantifying the effects of hydrogen concentration and cooling rates on porosity formation in Al-Li alloys

The addition of Li to Al alloys produces such benefits as a 6% increase of modulus and a 3% weight reduction upon adding 1 wt.% Li, and yet it has led to difficulties for manufacturing due to the highly active Li and 25 times equilibrium [H] concentration in the liquid at elevated temperatures. In this study, the 3D porosity morphology was quantified using the X-ray computed tomography (X-CT) from both sand gravity and vacuum castings. A cellular automaton model has been adopted to predict porosity distribution as a function of equilibrium hydrogen concentration and thermal boundary conditions. Combining experimental and simulation results, it was found that the mechanical properties of vacuum casting Al-Li alloy have been improved significantly due to the reduction of hydrogen porosity. The prediction of porosity as a function of hydrogen levels and cooling conditions agrees well with experiments, and porosity has been found to decrease Young's modulus and initiating cracks in Al-Li alloys.