Grain Boundary Pinning Approach for Manufacturing High-Strength Nanocrystalline Aluminum Alloys

Abstract

Nanostructuring is a commonly employed method to improve the mechanical properties of metals and alloys, but its usage is limited due to the instability of nanocrystalline (NC) materials. To address this challenge, the current study employs doping techniques to obtain a stable NC structure. In the present work, commercially pure aluminum (Al) powders were milled at cryogenic temperatures (a) without magnesium (Mg) and (b) with 5 wt.% of Mg powders for different durations. The unmilled and cryomilled powders were characterized to determine the changes in particle morphology, elemental composition, and crystallite size. The results showed changes in the morphology of powders and a reduction in crystallite size with the increase in cryomilling duration. Thereafter, the bulk samples using cryomilled powders were manufactured using two different methods (a) spark plasma sintering and (b) cold spray processes. The mechanical properties of the bulk samples were assessed by conducting Vickers microhardness, tensile, and fatigue tests. The tests were performed both at the University's laboratory and at an independent testing facility. The test results from both testing sources showed a significant improvement in mechanical properties for the Al-Mg bulk samples as compared to pure Al. The mechanism for the enhancement in mechanical properties as a result of crystallite size reduction and grain boundary strengthening by the addition of Mg dopant is discussed. The current study also examined the total energy consumption and manufacturing costs involved in the production process. The cost analysis revealed that manufacturing a kilogram of nanocrystalline aluminum alloy costs less than $90 inclusive of the energy costs.