Corrosion Behavior of Extruded AM60-AlN Metal Matrix Nanocomposite and AM60 Alloy Exposed to Simulated Acid Rain Environment

Abstract

The present work compared the initial stages of corrosion process development on the AM60-AlN metal matrix nanocomposite surface and on AM60, during their exposure for 30 days to simulated acid rain solution (SAR). The AlN nanoparticles were observed as “attached” to those of Mn-rich AlMn intermetallic particles, forming clusters. The introduction of 1.0 wt.% AlN (≈ 80 nm) in the AM60 alloy carried a slight grain refinement and favored the formation of a denser and more protective corrosion layer, suggested by the electrochemical impedance spectroscopy (EIS) values of higher charge transfer resistance (R2) and capacitance, characteristic of the double layer in the presence of corrosion products, and also suggested by Rn (EN) values, compared to those of the AM60 alloy. Thus, the concentration of the released Mg-ions from the composite surface was lower. Due to the increase in time of the SAR solution pH, Al de-alloying may occur, as well as Al(OH)3 formation, as confirmed by XPS analysis. Due to the presence of Cl-ions in SAR solution, localized corrosion was observed, suggested as fractional Gaussian noise of a stationary and persistent process in time, according to the PSD of the corrosion current fluctuations (EN).

AM60-AlN Nanocomposite and AM60 Alloy Corrosion Activity in Simulated Marine-Coastal Ambience

“…The aluminum nitride (AlN) nanoparticles (1.0 wt.%, average diameter of ≈80 nm) have been added under stirring (Tomsk State University, Russia) to the AM60 alloy. The characterization of the AlN nanoparticles has been reported [33,44,45]. The surface of the tested samples (10 mm of diameter and thickness of 2 mm) was polished (with SiC paper to 2000 grit), then sonicated in ethanol and dried at room temperature.…”

“…The real-field atmospheric testing may take several years, and the variety of different and specific environmental parameters makes it difficult to compare data. An alternative approach is to use accelerated tests that produce data in a shorter time, or model solutions, simulating the metal interface covered by a thin layer of 100% humidity [44,46]. The model solutions allow one to obtain comparative results and to control the parameters during electrochemical tests.…”

“…In our previous work [44], optical images of AM60-AlN and AM60 (longitudinal section, extrusion direction and cross-section) were reported. The introduction of the AlN nanoparticles resulted in a grain size reduction of 12% and in a slight 7% increase of the Vickers hardness of AM60 alloy.…”

“…Considering the effect of aggressivity of urban industrial atmospheres on the corrosion of metals, in our previous study [44], the AM60-AlN nanocomposite and AM60 alloy electrochemical activities have been characterized after exposure to an acid rain environment (SAR solution) for up to 30 days, which simulated the formation of aqueous layer at the metal surface at 100% air humidity. A denser and more efficient protective corrosion layer has grown on the composite alloy surface, ascribed to the AlN nanoparticles, which favored the slight grain size refinement of the nanocomposite.…”

Corrosion and Protection in Aeronautical Alloys

“…Chavez et al [3] conducted an investigation comparing the initial stages of corrosion process development on the AM60-AlN metal matrix nanocomposite surface and on AM60 during a 30-day exposure to simulated acid rain solution (SAR). The AlN nanoparticles were observed as "attached" to Mn-rich AlMn intermetallic particles, forming clusters.…”