The structure of interface between the Mg alloy and titanium which is a risk zone for the explosion welded composition as a whole has been investigated. Experiments were carried out for two composites produced in a “soft” and “hard” welding mode. It is ascertained that the soft explosion welding secures the higher quality of the weld joint. Exploitation properties of composites investigated is found to be deteriorated as colloid Mg-Ti system is formed. The models for voids formation in Mg under explosion loading are considered.