Plastic joining of open-cell nickel foam and polymethyl methacrylate (PMMA) sheet by friction stir incremental forming

Friction stir incremental forming (FSIF) process was applied to join a commercial open-cell type nickel foam with a polymethyl methacrylate (PMMA) sheet for fabrication of porous metal–nonporous resin composite. In this process, a rotating rod-shaped tool was vertically pushed and horizontally fed against the sheet on the foam. The sheet was frictionally heated and incrementally deformed by the rotating tool, while the cellular matrix of the foam was not plastically deformed. The sheet with a thickness of 1.0 mm was joined with the foam under FSIF conditions of rotation rate faster than 2000 rpm and feed rate slower than 60 mm/min. The joining strength between the foam and the sheet was investigated by performing tensile test. The joining strength was obtained over the fracture strength of the foam. The joining mechanism of the foam and the sheet was discussed from the microscopic observation of the foam–sheet interface and the temperature change in the sheet. It is concluded that the sheet was mechanically interlocked (anchored) to the porous structure of the foam by the plastic flow of the heated and softened PMMA into the surface pores of the foam.