EFFECT OF T6 TREATMENT ON THE HARDNESS OF CARBON NANOTUBE REINFORCED AA6061 ALUMINIUM ALLOY MATRIX COMPOSITES

摘要

The development aluminum matrix composites, using carbon nanotubes as strengthening dispersion phase, is of great interest for the transport sector, that continuously demands high strength-low density materials for efficient structures. In the present work, multiwall carbon nanotubes (MWCNT) were used to reinforce the AA6061 aluminium alloy. 1 and 2% (in weight) of MWCNT were mixed to the alloy powder by high-energy ball-milling process. The blended powder was consolidated by hot extrusion. The obtained composite bars were solution heat treated and aged to T6 temper, and characterized by optical and scanning electron microscopy, and by hardening testing. A typical wrought microstructure free of defects was obtained. Hardness of the composites was substantially increased for 2% MWCNT addition, milled for 10 h. The better performance for the composites blended at a higher milling time was supposed to be due to a better MWCNT dispersion. The effect of aging on the composite hardness was evaluated, and it was found that no benefits for the composite hardness were obtained after solution heat treatment followed by T6 aging according to SAE AMS2772 specification, when comparing to the as-extruded hardness values. Possible reasons for such composites behavior are discussed.