Influence of High-Energy Ball Milling on the Microstructure, Phase Composition, and Microhardness of the Al–Mn–Cu Alloy

The influence of the treatment time in a planetary ball mill on the morphology, phase composition, and microstructure of the Al–Mn–Cu-based alloy and the same alloy with nanodiamond particles is studied by X-ray diffraction and scanning electron microscopy. The phase composition of the alloy is determined by X-ray diffraction after casting and milling for 5–20 h. It is shown that nanodiamond particles contribute to the coarsening of granules. The effect was intensified with an increase in the milling time to 20 h. The granular size weakly depends on the processing time for the initial alloy. The Cu-bearing phases of solidification origin are dissolved during milling. The lattice parameter of the aluminum solid solution decreases after five hours of treatment to 0.4028–0.4030 nm, and it increases with further increase in milling time. Exothermic peaks associated with the precipitation of secondary phases are revealed for mechanically alloyed granules during heating. An increase in the milling time reduces the intensity of peaks. The solidus temperature of the alloys decreases after mechanical alloying. For the nanodiamond-bearing sample, a high-temperature exothermic effect, which can be associated to the formation of aluminum carbides or oxidation reactions in nanodiamond particles, is observed. The maximum microhardness is achieved after 5–10 h of milling, and the nanodiamond particles slightly increase the maximum microhardness from 316 to 330 HV. The results indicate the dissolution of copper and manganese in the aluminum solid solution during milling for 5 h and their precipitation with increasing milling time. Nanodiamond particles do not influence the dissolution of elements but accelerate the solid solution decomposition with increasing milling time.