Abstract
In the present work, the electrochemical behavior of WC-CoCr coatings with 10 (W10), 15 (W15) and 20 (W20) torch passes sprayed by High Velocity Oxygen-Fuel (HVOF) flame on AA7050 aluminum alloy substrate, evaluated in 3.5% NaCl solution, were compared using open-circuit potential (E OC) measurements, electrochemical impedance spectroscopy (EIS) and polarization curves. The coating surfaces and their cross sections were characterized by X ray diffraction and the Rockwell-C hardness test, and also by optical (OM) and scanning electron microscopy (SEM) before and after the corrosion tests. The electrochemical data showed that sample W10 presented higher corrosion resistance than the others in chloride solutions. In some tests, aluminum salts on the coating surface were identified by EDS, indicating the corrosion of the substrate. And using aluminon, aluminum ions were detected and analyzing the surface via stereomicroscopy, hydrogen bubbles were observed, both showing that the electrolyte reached the substrate and galvanic corrosion possibly occurred. The physical characterization showed that sample W10 presented a lower number of cracks and pores, justifying its higher corrosion resistance.
Highlights
Aluminum alloys have been chosen for the production of structural components of aircraft since about 1930
The WC-CoCr coatings were obtained via High Velocity Oxygen-Fuel (HVOF) spraying (CPT-Universitat de Barcelona) using a DJH 2700 gun, applying 10 (W10), 15 (W15) and 20 (W20) torch passes, using an oxygen (253 L/min) and propylene (69 L/min) mixture to partially melt the powder particles and spray them onto the aluminum alloy substrate
The number of torch passes influences the electrochemical behavior in 3.5% NaCl solution for coatings sprayed via HVOF on AA7050 aluminum alloy substrate
Summary
Aluminum alloys have been chosen for the production of structural components of aircraft since about 1930. Polymer matrix composites are being used extensively in high-performance military aircraft and specified for some applications in modern commercial aircraft, AA7050 aluminum alloys are the overwhelming choice for the plate, extrusions, hand and die forgings of aircraft structural parts. All structural materials are susceptible to some degradation from the environment, and aluminum alloy products used in aircraft are not an exception. Aluminum alloy products corrode in a localized manner either by pitting, intergranular attack or exfoliation[2,3,4]. It is well known that pitting corrosion in the AA7050 aluminum alloys is usually associated to constituent particles, and pitting may have a marked effect on the fatigue properties of these materials. Light metals in general exhibit very poor tribological properties resulting in severe superficial wear[5]
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