Abstract
This study investigates the mechanical properties of aluminium 2024 (Al-2024) and aluminium 7075 (Al-7075) cold-sprayed materials and coatings for repairs. It aims to determine the acceptable data needed to meet regulatory requirement when substantiating cold spray repairs. The study focuses on repairs of non-principal structural element (PSE) structures such as skin and panels that are prone to corrosion and wear. For cold spray repair of such components, the microstructure, tensile, peel, bearing, and bending strength from the repair process and powder materials of Al-2024 and Al-7075, were identified and investigated in accordance with MIL-STD-3021. Results show an average coating porosity of <1.2% for both materials. Average tensile strength was 247.1 MPa (with elongation of 0.76%) for Al-2024 and 264.0 MPa (with elongation of 0.87%) for Al-7075. Al-2024 has an average peel strength of 71.9 MPa, while Al-7075 is at 48.9 MPa. The Al-2024 bearing test specimens gave a maximum load strength before failure of 633.6 MPa, while the Al-7075 gave 762.7 MPa. The bending tests show good flexibility for coating thickness ranges of typical skin and panel parts. The results show that cold spray can be used to restore thickness and oversized hole diameters for Al-2024 and Al-7075 skin and panels. The bearing test conducted in this study has also demonstrated a new test method to determine the bearing load and yield strength of a cold spray-repaired hole in a plate.
Highlights
Cold spray is a spray deposition process which uses high-velocity gases to deposit metal powders from a “de Laval” nozzle with a converging-diverging internal geometry at velocities of more than Mach 1 [1,2]
This study investigated the mechanical properties of aluminium 2024 (Al-2024) and aluminium 7075 (Al-7075) cold-sprayed materials and coatings, with the intent to build up adequate understanding and data for cold spray repair, guided by the European Union Aviation Safety Agency’s (EASA) Part 21 requirements
Tensile strength was found to be of an average of 247 MPa for Al-2024 and 264 MPa for Al-7075
Summary
Cold spray is a spray deposition process which uses high-velocity gases (the commonly used gases are compressed air, nitrogen, and helium) to deposit metal powders from a “de Laval” nozzle with a converging-diverging internal geometry at velocities of more than Mach 1 [1,2]. With the release of USAF Structures Bulletin EZ-19-01 and the consideration of existing military standards (MIL-STD-1530D and JSSG-2006), a few applicability studies of Hartman-Schijve crack growth for cold spray repairs showed promising correlation with experimental data for durability and damage tolerance analysis (DADTA) [19,20,21]. These papers were for specific components and conducted with less than eight sample sizes in controlled environments. There is a lack of reliable cold spray material databases that can aid the in-field engineers with quick substantiation of their repair designs beyond dimension restoration
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