Corrosion Protection of Friction Stir Welded Al 7075 Panel for use in Aerospace Applications using Cold Gas Dynamic Spray

Title: Corrosion Protection of Friction Stir Welded Al 7075 Panel for use in Aerospace Applications using Cold Gas Dynamic Spray
Authors: Trahan, Patrick
Date: 2014-02-21
Abstract: The aerospace industry is constantly looking for methods to reduce the cost of flying their airplanes. These savings can come in many forms, one of them being cost savings attributed to fuel savings by either reducing the weight of the airplane or reducing the drag. Friction stir welding (FSW) was introduced as a means of joining previously unweldable Al 7075, a high-strength aluminum alloy commonly used in aerospace for its high specific strength. This eliminated the need for costly and time consuming rivets to be installed, firstly reducing the production cost of the airplane and secondly reducing the overall weight of the airplane therefore improving fuel consumption. There are many factors at play in the process of producing FSW Al 7075, but the result of this process creates a weld joint that is more susceptible to corrosion than the rest of the panel. For this reason, FSW Al 7075 panel fail prematurely and must be replaced too often. The main goal of this project is, using cold gas dynamic spray, to create a metallic layer on top of an Al 7075 FSW joint to protect it against corrosion. A series of 3 corrosion tests indicated that pure Al, among coatings of pure Al, Al 5038 and Al 7075, offered the best protection against corrosion. Al 5083 would also be a suitable material and should be used in applications where high bond strengths are required. Al 7075, although of the same alloy as the parent material, is not recommended for corrosion protection as it offered little advantage over the parent material. In order to better understand the interaction of creating a coating after a hot welding process, several analyses were performed. These included deposition at multiple substrate temperatures as well as hardness and velocity measurements. Results indicate that some aluminum alloys are very sensitive to temperature, yielding better coatings at high substrate temperatures. Individual particle deposition tests reveal that these improvements do not occur at the substrate-coating interface. Another portion of this project was dedicated to creating tensile specimens composed entirely of pure Al cold sprayed coatings. Several sets of samples were produced. Results indicate that pulling in the direction of nozzle travel direction yields UTS values 50% higher than pulling in the direction perpendicular to the direction of nozzle travel during coating deposition. Results after annealing seem to converge towards the same value. Finally, a new nozzle design was performed which should create a more efficient spraying process, resulting in cost savings for the industry.
CollectionThèses, 2011 - // Theses, 2011 -