Aluminum powder with different C and C–Cu mixtures powders were fabricated by powder metallurgy, using high-energy mechanical milling as a pre-treatment of powders. To evaluate the combined effect of the C–Cu mixture and the process conditions, such as sintering temperature/time and milling time, on the yield stress and hardness, two experimental designs were carried out. The results were analyzed with Minitab Statistical Software using contour plots. From the results, better mechanical properties were found at a Cu/C ratio of 0.33 and samples with high C content (3 wt. %). In samples subject to long sintering time (3 h), the mechanism of precipitation of the second phase was mainly present, resulting in an improvement in mechanical properties. From the difference found between the elastic limit and the microhardness tests, it was found that there was an inefficient sintering process affecting the elastic limit test results. Additionally, X-ray analyses using the Rietveld program, were used for microstructural characterization and mechanical parameters of yield strength and ultimate tensile strength.

By superposition, the individual strengthening mechanisms via hardness analyses and the particle dispersion contribution to strengthening were estimated for Al–C and Al–C–Cu composites and pure Al. An evident contribution to hardening due to the density of dislocations was observed for all samples; the presence of relatively high-density values was the result of the difference in the coefficients of thermal expansion (CTE) between the matrix and the reinforced particles when the composites were subjected to the sintering process. However, for the Al–C–Cu composites, the dispersion of the particles had an important effect on the strengthening. For the Al–C–Cu composites, the maximum increase in microhardness was ~210% compared to the pure Al sample processed under the same conditions. The crystallite size and dislocation density contribution to strengthening were calculated using the Langford–Cohen and Taylor equations from the microstructural analysis, respectively. The estimated microhardness values had a good correlation with the experimental. According to the results, the Cu content is responsible for integrating and dispersing the Al4C3 phase. The proposed mathematical equation includes the combined effect of the content of C and Cu (in weight percent). The composites were fabricated following a powder metallurgical route complemented with the mechanical alloying (MA) process. Microstructural analyses were carried out through X-ray analyses coupled with a convolutional multiple whole profile (CMWP) fitting program to determine the crystallite size and dislocation density.

High-energy ball milling is a process suitable for producing composite powders whose achieved microstructure can be controlled by the processing parameters. Through this technique, it is possible to obtain a homogeneous distribution of reinforced material into a ductile metal matrix. In this work, some Al/CGNs nanocomposites were fabricated through a high-energy ball mill to disperse nanostructured graphite reinforcements produced in situ in the Al matrix. To retain the dispersed CGNs in the Al matrix, avoiding the precipitation of the Al4C3 phase during sintering, the high-frequency induction sintering (HFIS) method was used, which allows rapid heating rates. For comparative purposes, samples in the green and sintered state processed in a conventional electric furnace (CFS) were used. Microhardness testing was used to evaluate the effectiveness of the reinforcement in samples under different processing conditions. Structural analyses were carried out through an X-ray diffractometer coupled with a convolutional multiple whole profile (CMWP) fitting program to determine the crystallite size and dislocation density; both strengthening contributions were calculated using the Langford–Cohen and Taylor equations. According to the results, the CGNs dispersed in the Al matrix played an important role in the reinforcement of the Al matrix, promoting the increase in the dislocation density during the milling process. The strengthening contribution of the dislocation density was ~50% of the total hardening value, while the contribution by dispersion of CGNs was ~22% in samples with 3 wt. % C and sintered by the HFIS method. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to analyze the morphology, size, and distribution of phases present in the Al matrix. From the analyses carried out in AFM (topography and phase images), the CGNs are located mainly around crystallites and present height profiles of 1.6 to 2 nm.