Modelling of carbon nanotube dispersion and strengthening mechanisms in Al matrix composites prepared by high energy ball milling-powder metallurgy method

Carbon nanotube (CNT) reinforced Al-5Mg composites were prepared by combining ball milling, hot-pressing and subsequent hot extrusion. CNT distribution during milling and strengthening mechanism of the composites were investigated. A model based on the ratio of minimum necessary time for uniformly dispersing CNT to flattening time of composite powders was proposed to analyze the effect of milling rotation rate on CNT distribution, and it indicated that both low and high milling rotation rates are not beneficial to CNT distribution, due to small deformation ratio and severe cold-welding, respectively. Under a milling rotation rate of 400 rpm, CNTs could be uniformly dispersed after 8 h of milling and aligned along the extruding direction after extrusion. Elastic moduli and strengths of the composites were significantly increased. Load transfer, grain refinement, and mismatch dislocation mechanisms were determined to contribute to the strength increase of CNT/Al-5Mg composites.