Effect of milling time on microstructure and hardness of AA7075-15 wt% SiC-1 wt% MWCNT nanocomposite

Abstract

In this study, the effect of ball milling on microstructure and hardness of Al7075 - 15 wt% SiC - 1 wt% MWCNT nanocomposite was investigated as a function of milling time up to 20 h. Mechanically alloyed powders were consolidated by cold pressing followed by sintering at 560°C for 1 h in an argon atmosphere. The structural characterization of nanocomposites was conducted by a X-ray diffractometer (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and grain size analyses. The hardness of samples was measured by using Wolpert Wilson-400 micro-hardness testing equipment comprising of a Vickers indenter. The structural defects of pristine and milled MWCNTs were calculated by using defect and carbon intensity ratio (I_D/I_G) resulted from Raman spectroscopy. The results indicate that after ball milling, the grain size decreases depending on the milling time, the intermetallic Al₄C₃ phase is formed as a result of the reaction between the matrix and the MWCNT particles, and the MWCNT structure is destroyed. The finest grain size and highest hardness values were obtained as 483 nm and 134 HV, respectively, after 15 h of grinding.