Modeling and numerical study of the molten pool dynamics during scanning electron beam welding of aluminum alloys: Physical mechanism, prediction and parameter selection

•A three-dimensional molten pool model that involves an innovative heat source model is developed to reveal the physical mechanism in scanning electron beam welding.•A Gaussian process regression model trained with simulated data is developed to rapidly predict the weld dimensions.•The keyhole velocity, periodic length and stirring Reynolds number are proposed to quantify the molten pool stability.•A parameter selection method is proposed based on theoretical analysis to optimize and control the actual welding process.