Surface characterisation of DC plasma electrolytic oxidation treated 6082 aluminium alloy Effect of current density and electrolyte concentration

Plasma electrolytic oxidation (PEO) is a specialised but well-developed process which has found applications in aerospace oil/gas textile chemical electrical and biomedical sectors A novel range of coatings having technologically attractive physical and chemical properties (e g wear- and corrosion-resistance) can be produced by suitable control of the electrolyte as well as electrical parameters of the PEO process Oxide ceramic films 3 to 40 mu m thick were produced on 6082 aluminium alloy by DC PEO using 5 to 20 A/dm(2) current density in KOH electrolyte with varied concentration (0 5 to 20 g/l) Phase analysis (composition and crystallite size) was carried out using X-ray diffraction and TEM techniques Residual stresses associated with the crystalline coating phase (alpha-Al2O3) were evaluated using the X-ray diffraction Sin(2)psi method Nanoindentation studies were conducted to evaluate the hardness and elastic modulus SEM SPM and TEM techniques were utilised to study surface as well as cross-sectional morphology and nano features of the PEO coatings Correlations between internal stress and coating thickness surface morphology and phase composition are discussed It was found that depending on the current density and electrolyte concentration used internal direct and shear stresses in DC PEO alumina coatings ranged from -302 +/- 19 MPa to -714 +/- 22 MPa and -25 +/- 12 MPa to -345 +/- 27 MPa respectively Regimes of PEO treatment favourable for the production of thicker coatings with minimal stress level dense morphology and relatively high content of alpha-Al2O3 phase are identified (C) 2010 Elsevier B V All rights reserved