Assessment of Corrosion and Scratch Resistance of Plasma Electrolytic Oxidation and Hard Anodized Coatings Fabricated on AA7075-T6

• Published in: Transactions of the Indian Institute of Metals Vol. 74; no. 8; pp. 1991 - 2002
• Main Authors: Premchand, C., Hariprasad, S., Saikiran, A., Lokeshkumar, E., Manojkumar, P., Ravisankar, B., Venkataraman, B., Rameshbabu, N.
• Format: Journal Article
• Language: English
• Published: New Delhi Springer India 01.08.2021; Springer Nature B.V
• Subjects: Adhesive strength; Alternating current; Aluminum base alloys; Aluminum oxide; Aqueous electrolytes; Ceramic coatings; Chemistry and Materials Science; Corrosion; Corrosion and Coatings; Corrosion currents; Corrosion resistance; Corrosion tests; Current density; Electrolytes; Emission analysis; Field emission microscopy; High strength alloys; Materials Science; Metallic Materials; Original Article; Oxidation; Oxidation resistance; Oxide coatings; Phase composition; Potassium hydroxides; Power sources; Scratch resistance; Sodium silicates; Tribology; Corrosion resistance; Electrolyte composition; AA7075-T6; PEO; Type II hard anodization; Adhesion strength
• ISSN: 0972-2815; 0975-1645
• DOI: 10.1007/s12666-021-02289-4

Surface modification of high-strength aluminium alloy 7075-T6 by plasma electrolytic oxidation (PEO) and type II hard anodization (HA) is presented in the current work. PEO-based ceramic oxide coatings were fabricated by employing an alternating current (AC) power source with a current density of 300 mA/cm 2 . The concentration effect of electrolytes on the alumina coatings was investigated and optimized comprehensively. Three separate aqueous electrolytes with 1:3, 1:1 and 3:1 proportions of sodium silicate (Na 2 SiO 3 ) and potassium hydroxide (KOH) were utilized to evaluate optimum electrolyte concentration for obtaining desired AC-PEO coatings. X-ray diffraction (XRD) was utilized to investigate the phase composition of the coatings. Field emission scanning electron microscopy (FESEM) was employed to investigate the surface and cross-sectional characteristics of oxide coatings. Scratch testing was used to assess the oxide coatings' adhesion ability, and potentiodynamic polarization (PDP) was utilized to assess the coatings' corrosion behaviour in a 3.5 wt% aqueous NaCl solution. Among the AC-PEO and HA coatings, the AC-PEO specimen fabricated with equal ratios of sodium silicate and KOH concentration (Na 2 SiO 3 :KOH 1:1) showed excellent adhesion strength (critical load, L c  = 41.5 N) along with the remarkable corrosion resistance (corrosion current density, i corr  = 5.63 × 10 –6  mA/cm 2 ).