Application of ball milling in the synthesis of Al7075 composites containing carbon nanotubes.

Abstract

Through powder metallurgy techniques, it is intended to obtain a metal matrix composite (MMC) of 7075 aluminum alloy reinforced with 1% of multiple wall carbon nanotubes (MWCNTs), which after hot extrusion present mechanical properties similar or even superior to the conventional AA7075 alloy in condition T6. This MMC should be able to be welded by friction stir welding (FSW), thus avoiding the disadvantages presented by the hardenable alloys by precipitation in the welding process. This work focuses on the optimization of the dispersion stage of the MWCNTs in the prealloyed powders of the matrix. For this, three mechanical ball milling strategies are compared. In the first, the pre-alloyed powders and MWCNTs are milled together following a cycle of variation of low energy rotation speeds (LE) (300-200rpm). The second also performs the milling of the mix of powders and nanotubes  by varying the rotation speed in a high energy cycle (HE) (1300-1200rpm). In the third one (H + LE), powders of 7075 are initially milled at high folowing a cycle of high rotation speed (high energy), followed by a low rotation speed stage (low energy) in which the MWCNTs are mixed. From the morphological characterization by SEM and determination of the crystallite size of the powders (XRD), a complete discussion of each of said pathways is carried out.