The Effect of TVAC Cycles on Physical Properties and Morphology of Alumina Coated AA7075 via Hard Anodization and Pulsed Laser Deposition: A Comparative Study for Space Applications

Abstract

Abstract. Aluminium alloys used in space structural applications are exposed to extreme environmental conditions. To preserve the integrity of structural materials in such environments, various surface treatments have been developed with the goal of forming thin films of hard oxides. Traditionally, the standard surface treatment for space applications has been hard anodization, which produces aluminium oxide layers through an electrochemical reaction between the substrate and an electrolyte. As an alternative to this well-established technique, thin film deposition via Pulsed Laser Deposition (PLD) has been explored. This study compares the traditional hard anodization method with PLD to evaluate their respective strengths and weaknesses and assess the potential of PLD as a viable alternative to coat AA7075-T6, a widely used alloy in the space industry. This work examines the effects of Low Earth Orbit (LEO) conditions on the morphology and on the interface between the aluminum substrate and the deposited alumina. The LEO environment experienced by the “6S CubeSat” of the PoliSpace project [1] is simulated through thermal cycling in a Thermal Vacuum Chamber (TVAC), in accordance with the “ECSS-E-ST-10-03C” standard. The samples underwent a tailored thermal cycle, in which the maximum and minimum temperatures represent limiting conditions selected to prevent damage to sensitive components, such as the structural batteries. A high vacuum level was ensured during each test to fully simulate the space environment. The physical and elastic properties of both coatings were evaluated employing Brillouin spectroscopy, offering insights into how the fabrication method influences the final characteristics of the deposited films. Visual tests confirmed the different nature of the two interfaces and the expected higher compactness of the PLD-deposited alumina with respect to the anodic one.