Modeling of microstructure formation with gas porosity growth during columnar dendritic solidification of aluminum alloys

Abstract

In this paper, microstructure formation with gas bubble growth during columnar dendritic solidification has been numerically investigated by using the coupled lattice Boltzmann-cellular automaton-finite difference (LB-CA-FD) model, which combines the physical mechanisms of the redistribution of hydrogen components at the solid–liquid interface and the transportation of hydrogen atoms in liquid. Hydrogen transportation, bubble nucleation and growth are computed by the LB method while the growth of columnar dendrite and the transport of solutes are described by the CA-FD model. Predicted results show that the bubbles begin to nucleate at the roots of primary dendritic trunk and secondary arms, and elongated irregular bubbles are sandwiched between neighboring dendrites after merging and moving during the growth stage. Columnar dendritic change from coarse and ordered to fine and disordered as the cooling rate is increased. Meanwhile, the cooling rate has a significant effect on the incubation time for gas bubbles and the maximum growth rate of porosity. It was found that the misorientation angle has limited effects on the solid fraction and porosity percentage but strongly influences on the morphologies of the columnar dendritic arrays, resulting in the different distributions of bubbles.