Magnetic pulse welding is a solid state impact welding process, similar to explosive welding, which produces metallurgical bond by oblique high-speed impact between two metal bodies. This violent impact removes the metal surface oxide layers and then joins the two atomic level clean metal surfaces together by the incidental compression pressure. The impact velocity is at 200-400 m/s and the being welded metal surface undergoes severe plastic deformation with strain rate in the order of 10(6)-10(7) s(-1). The ultrafine-grained structure was observed on the welded interface. This article studied two types of similar material lap joint interfaces and the base metals were aluminum alloy 6061 and copper alloy 110. Nano-indentation testing shows that the welded interfaces have significantly greater hardness than the base metals. The interface microstructure was studied by optical microscopy, electron backscatter diffraction microscopy, and transmission electron microscopy. The welded aluminum alloy 6061 interface exhibits extremely fine grains and an extremely high dislocation density. The impact welded copper alloy 110 interface presents nano-scale lamellar band structure and deformation twins. The interface hardness increasing was attributed to this impact-induced microstructural refinement.