X. Li, M. Liese, M. Sokoluk
University of California, Los Angeles,
Keywords: aluminum, 7075, 7050, 2024, 6061, high strength aluminum, WAAM, wire arc additive manufacturing, additive manufacturing, nanotechnology, nanotech metallurgy, aerospace, defense, metal revolution
Summary:Light materials are of paramount importance and tremendous industry interest can be found in order to reduce fuel consumption and emission. The key to success would be to reduce the weight of constructions or vehicles. For example, a 10% weight reduction results in a 6-8% increase in fuel economy for automobiles. Additive manufacturing with advantages in material, time and energy savings is very promising in order to achieve the aforementioned goals. Additionally, topology optimization and further weight reduction can be achieved with additive manufacturing. Especially in cooperation with high strength aluminum alloys as deposition material, enormous savings can be realized with only minor reduction in strength, compared to steel. Besides some applications in aerospace and military industry, high strength aluminum alloys like the 2000 and 7000-series were underrepresented in the manufacturing industry. Even though these alloys achieve superior strength-to-weight ratios, the restricted utilization of these high strength aluminum alloys is the result of extremely low weldability due to high strength aluminum alloys’ notorious susceptibility to hot cracking. A breakthrough happened with the incorporation of nanoparticles into the alloys and it enabled weldability and additive manufacturing of high strength aluminum alloys (Sokoluk et al., 2019). The achieved hot-crack resistance enabled by this novel technology opens new avenues for these high strength alloys for additive manufacturing. Every additive manufacturing process involves a fusion process and therefore metal additive manufacturing requires melting and solidifying of the used metal feedstock. Thus, metal additive manufacturing is restricted to non-crack-susceptible materials In this work, Wire Arc Additive Manufacturing (WAAM) was used to print high strength 2024 and 7075 aluminum components. The resulting parts were crack-free and showed exceptional grain morphology and supreme mechanical properties. In addition, hardness and tensile strength of the deposited demonstrators were tested, and supreme values for both characteristics could be discovered. Repeated heating cycles, that come with the WAAM process cause difficulties in terms of grain structure. Under these conditions it is very unusual that the grain size remains stable and constant from top to bottom throughout different layers, since the repeated heating cycles are prone to cause grain growth in the lower layers of the product. In contrast, micro- and nanostructure analysis of the deposited high strength aluminum parts showed continuous small grain sizes without grain growth throughout the different layers. The homogeneous grain structure and the exceptional mechanical properties achieved in this work demonstrate the potential that WAAM combined with Nanotech Metallurgy has to offer. Grain structure and solidification behavior of high strength aluminum alloys were successfully controlled in the WAAM process. With this in mind, nano-treated high strength aluminum alloys, like the AA2024and AA7075 alloys used in this work, have the potential to become conventionally adapted in order to manufacture high strength crack free parts with exceptional mechanical properties.