Abstract: Metal matrix composites face the trade-off dilemma of strength and ductility because of the aggregation tendency of reinforcements at powder or grain boundaries. Ball milling is an efficient method of dispersing reinforcements in metals; however, the homogeneity and content of dispersed reinforcements were limited by the intrinsic cold-welding tendency of deformed composite powders. In this study, a repeating deformation ball milling (RDBM) process was designed to prevent the cold-welding phenomenon of aluminum (Al) matrix composite powders and restart the plastic deformation process to acquire homogeneously intragranular dispersion of carbon nanotubes (CNTs). Results showed that intragranular CNT content increased by 41.6 % in the RDBM composite powders than that of conventional ball-milled composite powders. Consequently, an extraordinary increase in both tensile strength and ductility was observed in the RDBMed composite, compared with conventional ball-milled composites. Thorough microstructural characterizations, theoretical strength calculation, and loading-unloading-reloading experiments were conducted to understand the excellent mechanical properties. The RDBM process proposed in this study provides a new strategy to improve the dispersion of nano reinforcements and high performance in metal matrix composites.

Key words: Aluminum matrix composites (AMCs), Carbon nanotubes (CNTs), Intragranular reinforcement, Mechanical property