Thermal Stability and Microstructure of Nanometric 2024 Aluminum Alloy Powder Obtained by Cryogenic Milling and Spark Plasma Sintering
Metals and nanocrystalline alloy powders can be produced by high-energy milling and be consolidated by sintering techniques; the use of relatively low sintering temperatures maintains nanometric grains by avoiding grain growth. In the present study, 2024 aluminum alloy powders were produced by milling at cryogenic temperatures (cryomilling) and consolidation using spark plasma sintering (SPS). The thermal stability and microstructure of the nanometric 2024 Al alloy powder produced by cryomilling were analyzed. The milled powder was degassed to improve its sintering behavior and avoid the presence of pores in the final sintered piece. When the material was consolidated by SPS at a temperature of 525 ºC and under a pressure of 60 MPa, the resulting alloy density was 98% and an ultra-fine grained (100-300 nm)/micrometric microstructure. The hardness and microhardness of the milled degassed sintered samples showed values superior to atomized samples. The material also presented nanopores in the grain boundaries, very fine precipitates of AIN, rounded θ phases (Al2Cu), and elongated S phases (Al2CuMg).