Study on effects of hot isostatic pressing process on microstructure and properties of CNTs/Al2009 composites

The CNTs/Al2009 composite powders were prepared by cryogenic milling method and then the CNTs/Al2009 matrix composites were fabricated by hot extrusion process or hot isostatic pressing (HIP)/hot extrusion process. The effects of HIP process on microstructure and interface structure of CNTs/Al2009 composites were studied by X-ray diffraction, raman spectroscopy, scanning electron microscopy and transmission electron microscope. Finally, the effects of HIP process on the CNTs/2009Al composites were characterized by tensile strength at room temperature. The results showed that the cryogenic milling process could disperse 1.0 wt. % of CNTs into the aluminum matrix, and the composites prepared by HIP and hot extrusion process had uniform microstructure and excellent tensile properties at room temperature. The tensile strength, yield strength and elongation of the 1.0 wt.% CNTs/Al2009 composites prepared by HIP and hot extrusion process were 560 MPa, 443.3 MPa and 10.2%, respectively. Hot isostatic pressing process had an important influence on the interfacial bonding strength of CNTs/Al2009 composites. The strength of the composite prepared by HIP and hot extrusion process was 20 MPa higher than that of direct hot extrusion process, and the elongation was basically the same. The main reason was that the high temperature and high pressure conditions of hot isostatic pressing process could promote the reaction of carbon and aluminum at the interface between CNTs and aluminum matrix, so that a few CNTs with severe damage and defects in some CNTs formed Al4C3 phase with aluminum, thereby improving two compatibility, and enhanced interface bonding.