Corrosion protection of aluminium metal–matrix composites by cerium conversion coatings

Abstract

Effect of cerium pretreatment on the corrosion inhibition characteristics of AA6061 T6 alloy-10% Al 2 O 3 metal-matrix composite was investigated in aerated 3.5% NaCl solution after different immersion times ranging between 1 and 60 days at room temperature. Series of specimens were prepared under the following conditions: as-polished; directly treated in CeCl 3 ; alkaline etching followed by CeCl 3 treatment; immersion in boiling water followed by CeCl 3 treatment; and alkaline etching followed by immersion in boiling water and then CeCl 3 treatment. Electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion behaviour of treated and untreated specimens. The EIS was measured by perturbing the free corrosion potential of the specimens with 10 mV a.c. with a frequency decreasing from 10 mHz to 65 kHz. Polarization tests were used to investigate the perfect passivity domain after corrosion. Optical microscopy and SEM were used to investigate the occurrence of localized corrosion due to chloride ion attack. Specimens untreated, directly treated in CeCl 3 and alkaline etched followed by CeCl 3 treatment suffered from pitting as well as crevice corrosion after 30 days of immersion in NaCl. Conversely, the specimens after alkaline etching followed by oxide thickening in boiling water before cerium treatment showed promising corrosion protection even after 60 days of immersion in NaCl. The degree of protection depends to a high extent on the specimen preparation prior to cerium pretreatment.

Evaluation of different sealing methods for anodized aluminum‐silicon carbide (Al/SiC) composites using EIS and SEM techniques

“…Lightweight aluminum alloys matrices reinforced with silicon carbide (SiC) particles possess higher tensile strength and ductility at 300-400 8C and lower coefficient thermal expansion, but the use of these materials has been limited partially because they suffer from localized corrosion in the form of pitting in solutions containing chloride [6][7][8][9]. Aluminum alloys are usually chromated, painted, oxidized, or anodized in chromic, phosphoric, or sulfuric acid solutions to improve their corrosion resistance under a variety of aggressive atmospheric conditions [10][11][12][13][14].…”

Electrosynthesis of Polyaniline Film on AA 7075 Alloy and Its Corrosion Protection Ability

“…Hamdy also reported that the direct treatment cerium solution does not provide good corrosion protection for aluminum alloys. 41 They also confirmed the presence of localized corrosion even after a long cerium treatment. The mechanism of corrosion inhibition due to cerium depends on the incorporation of cerium ions through the pores of the Al oxide layer to block the active surface sites ͑cathodic inhibitor͒.…”

“…The mechanism of corrosion inhibition due to cerium depends on the incorporation of cerium ions through the pores of the Al oxide layer to block the active surface sites ͑cathodic inhibitor͒. 41 Jakab and Scully established that the corrosion inhibition of AA 2024-T3 is possible with metal ions released from an amorphous Al-Co-Ce alloy located in close proximity to the defect. 42 They explained that protection of alloys exposed at coating defects is demonstrated by inhibitor ion release in addition to barrier function and sacrificial cathodic protection.…”

Effect of surface preparation prior to cerium pre-treatment on the corrosion protection performance of aluminum composites

“…The most probable source of silicon is the matrix, where silicon is mainly concentrated at the interface between the matrix and alumina particles. Another source is the dissolution of silicon from glass during the pickling process by KOH [22,23,25].…”

“…However, data reported to date suggest that conversion coatings based on cerium, have various disadvantages such as nonuniform distribution [16,[19][20][21]. In the first part of this work, Hamdy et al [22,23] studied the effect of cerium pre-treatments on the corrosion behavior of aluminum composites. Results showed that direct cerium pretreatment slightly improved the surface protection against localized corrosion.…”