Peculiarities of Solidification Structure of Aluminum-lithium Alloy Welds

A kind of fine equiaxed smooth grains,which is different from equiaxed dendrites in both morphology and formation mechamism,was observed in 8090 Al-Li alloy welds.The fine equiaxed smooth grains mainly existed near the fusion boundaries and grew into a band along the solidification-pause lines in the welds.It was found that the existence of a particular solidification condition(i.e. smaller constitutional undercooling degree) as well as the elements of zirconium and lithium was necessary for the fine equiaxed smooth grains to form. Fractures which pass through the fine grain zone are predominately intergranular,since there is a larger amount of second phase along the grain boundaries of this zone.