The overarching objective of this limited scope project was to attain a fundamental understanding of the microstructural evolution and inherent material characteristics associated with aluminum alloys used in aircraft components and structural members repaired using the Wire Arc Additive Manufacturing (WAAM) process. Solidification and heat transfer models that form the basis for the development and demonstration of effective repair processes for aircraft components were sought to be developed. A foundation for future efforts to expand the models for the entire process and eventual incorporation of machine learning was provided by the initial modeling work. Alloy selection was based on available weld wire, weldability and the components obtained to be repaired. Development of process parameters for WAAM has been performed on 2xxx, 5xxx and 7xxx alloys, but not 6xxx series.

In this project, an ideal approach to developing an additive repair process by using a design of experiments that addressed performance, repeatability and reliability was implemented. The project team used a “Materials by Design” approach, to develop an understanding of the fundamental principles associated with the WAAM process through thermal and solidification models in combination with an aggressive materials characterization plan. Emphasis was placed on the development of the thermal and solidification models applied over a range of heat inputs using constant voltage, cold metal transfer arc welding, as well as low heat pulsed or synergic arc welding processes. The models determined the effects of composition, solidification conditions, and heat treating techniques on the microstructure and resulting mechanical properties of the WAAM material, substrate, and the demonstration of WAAM for repair of aircraft components. This systematic approach was verified by empirical data, alleviating the number of deposition trials and discovery by trial and error.

The project team successfully enabled the repair of a super hornet A356 oil pump casting that will greatly extend its life cycle and operational performance by implementing a hybrid modeling approach that leveraged both physical models and experimental data. The development of solidification and heat transfer models formed the basis for the development of an effective repair processes for aircraft components. A more fundamental understanding of the microstructural evolution resulting from the WAAM process specific to repair of aluminum aerospace alloys was determined by physics-based modeling substantiated by experimental data.

This work will advance the state-of-the-art for WAAM alloys by providing a better understanding of the microstructural evolution of aluminum alloys used in aircraft components. Significant energy, material, time and cost savings can be realized by implementing the WAAM process. The total cost savings of this approach is estimated to be at least $15 million dollars per year based upon the manufacturing data from the Department of Defense. This approach will form the foundation for additional development needed to repair a wide range of components. An additional benefit of WAAM is the ability to fabricate obsolete components or components that cannot be repaired. The use of WAAM to fabricate new components could allow the use of lower cost or higher performance materials in new aircraft.