Using molecular dynamics simulation we have investigated the melting properties of a 2-dimensional system of ions interacting through a screened Coulomb potential in the presence of a substrate. We focus on the role of the substrate potential in the melting transition. The physical system we study is the stage-2 graphite intercalation compound RbC24 and a related system RbC24.57 whose intercalant density differs from the former by a small amount. Our results reveal the nature of melting processes characteristic of periodic domain wall solids.