Mixing of carbon nanotubes (CNTs) and aluminum powder for powder metallurgy use

In recent years, carbon nanotubes (CNTs) reinforced aluminum matrix composites (AMCs) have attracted increasing attention. The quality of dispersion, however, is a crucial factor which determines the homogeneity and final mechanical properties of these composites. This work studied the mechanical mixing methods, viz. high energy and low energy ball millings, and compared them to a novel polyester binder-assisted (PBA) mixing method. Experimental results showed that the high energy and low energy ball-milled CNTs disintegrated and there were residual stresses, unlike the PBA-CNTs. The CNT dispersion conditions by these three methods were discussed. The Al-CNTs mixture was subsequently consolidated by powder metallurgy (PM) technique. Small addition of CNTs (0.5 wt.%) evidently improved the tensile strength and hardness of the composite by comparing with the pure matrix. Mechanical property enhancements of the Al-0.5CNT composites from PBA and high energy ball milling were superior to that mixed by low energy ball milling. This showed good dispersion effect in PBA and high energy ball milling technique.

Graphical AbstractThe PBA-CNTs were coated on the surface of Al powder. The high energy ball-milled CNTs were well dispersed, though not sufficiently distributed within Al powder. These high energy ball-milled CNTs disintegrated and there were residual stresses in the tubes. By comparison, the low energy ball-milled CNTs were intermediate between the above two, in terms of damage.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► The high energy ball-milled CNTs were well dispersed; there were residual stresses in the tubes. ► The PBA-CNTs were coated on the surface of Al powder; CNTs structure and morphology maintained in its original form. ► By comparison, the low energy ball-milled Al-CNTs were intermediate between the above two, in terms of dispersion and damage.