Effect of graphite additives on microstructure and mechanical properties of Al-Cu composites prepared by mechanical alloying and sintering

Al-Cu matrix composites with 5 wt% of graphite nanoplatelets additives were prepared using mechanical alloying (MA) of elemental Al-Cu-C powder mixtures followed by hot pressing at 480-510 degrees C and 30 MPa. The obtained powders and sintered samples were studied using scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and Raman spectroscopy. MA of Al-Cu powders during 8 h with and without graphite additives resulted in formation of approximately the same final phase composition: Cu9Al4 + CuAl2 + Al(Cu), but Al-Cu-C powders contained a larger volume fraction of highly refined particles. The crystalline structure of the graphite additives was shown to transform into amorphous one during MA and into Al4C3 phase during the consequent sintering. The influence of graphite additives on microstructure and mechanical properties of sintered Al-Cu composites is considered. Possible strengthening mechanisms for Al-Cu and Al-Cu/C composites are discussed.