Fabrication of MWCNT-reinforced Al composite local foams using friction stir processing route

The aim of the present research is the fabrication of MWCNT-reinforced Al composite foams on localized regions of metallic parts using a novel friction stir processing (FSP) route. This route consists of friction stir processing passes for the integration of the foaming and the stabilizing agents in the aluminum matrix (precursor specimens) and a separate foaming stage at a laboratory furnace. The precursor specimens were manufactured by mixing a blowing agent powder (0.4% w/w TiH2) and a stabilization agent nanopowder (2% w/w MWCNT) into the aluminum alloy matrix (AA5083-H111), using the intense stirring action of FSP. The porous aluminum obtained at the foaming stage has a medium porosity of 54% with a high circularity of pores. The microstructural investigation was performed by means of optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) technique. All of the above were correlated with microhardness distribution in both the precursor and the foamed specimens. The microstructure was found to be closely related to microhardness distribution perpendicular to the traversing direction of the FSP tool for both precursor and foamed specimens.