PM Synthesis and Characterization of Nano-SiC Reinforced Al 2124 and Al 6061 Aluminum Alloys

Abstract

Metal matrix composites (MMCs) have received an appreciable attention due their unique properties over conventional materials. The advantages of MMC have positioned them as suitable materials for multiple structural- and thermal management-applications in addition to wear service benefits. The most used metals as a matrix in research and development and in industries are aluminum and its alloys. This global recognition, embraced by the wide-range application, is due to aluminum light weight, excellent corrosion resistance and low cost. Silicon carbide (SiC), on the other hand, becomes the main type used as filler for aluminum and its alloys due to its exceptional mechanical and physical-chemical characteristics. As a ceramic reinforcement, it enjoys the remarkable hardness, yield strength, low density and thermal expansion. This useful combination yields to compromised values of the toughness of the matrix and hardness, strength, wear resistance and stiffness of the hard particles. Nevertheless, the current methodologies for fabricating Al/SiC composites face challenges, which include homogenous distribution of SiC in the Al matrix. Therefore, mechanical milling is utilized in this research to develop Al 2124 and Al 6061 nanocomposites reinforced with nano-sized SiC. It has been proven that after 5 hour of milling, a comparable homogenous distribution is attained with crystallite sizes in the range of 20 nm by using XRD and SEM. Consolidation of the developed nanocomposites was carried on using non-conventional technique; i.e. spark plasma sintering (SPS) versus a conventional hot isostatic pressing (HIP). Values of micro-hardness were improved with increasing nano-SiC content from 0,5,10 and 15 (117, 188, 241 and 256 Hv, respectively) for Al 2124 composites sintered at 500 °C using SPS. Densification, also, was found to increase with increasing sintering temperature from 400 °C to 500 °C and to decrease with nano-SiC content. However, sintering at 450 and 500 °C showed higher densification with increasing the content of nano-SiC as opposed to 400 °C. SPS, in general, gave improved densification and hardness values due to the different mechanism of heating. The maximum densification by SPS reached 98% for Al 6061/ 15% SiC and hardness value (211 Hv) sintered at 500 °C, while HIP only achieved 85% and (145 Hv) for the same alloy.