Abstract
PEO coatings were developed under voltage-controlled mode on a rheocast A356 aluminum alloy without and with pretreatment by conventional anodizing in sulphuric acid. Microstructure and composition of uncoated and coated materials were studied using SEM, EDS and XRD. The anodic precursor oxide layer preserves the microstructure of the alloy because of the presence of secondary phases having a different behavior relative to the matrix during conventional anodizing. After PEO treatment, the coatings consisted of a mixture of α-Al2O3, γ-Al2O3, SiO2 and mullite (3Al2O3·2SiO2). The effect of pre-anodizing on energy efficiency was investigated revealing considerable energy savings with the precursor porous films, because of the faster establishment of the so-called ‘soft sparking’ regime that promotes faster coating growth rate. The electrochemical corrosion properties were evaluated for uncoated and coated materials using electrochemical techniques (potentiodynamic curves and electrochemical impedance spectroscopy). PEO coated materials showed remarkably reduced susceptibility to corrosion.
DOI Link to Publication