INVESTIGATION OF THE EFFECTS OF DIFFERENT RETROGRESSION AND RE-AGING PARAMETERS APPLIED TO THE 7075 ALLOY ON THE MICRO-ARC OXIDATION PROCESS

Abstract

In this paper, retrogression and re-aging (RRA) heat treatment was applied to 7075 aluminum alloy in T6 condition at different times (30 and 90[Formula: see text]min) and temperatures (180∘C and 240∘C). While RRA heat treatments increase the corrosion resistance of the material, it does not harm its mechanical properties. On the other hand, the surface resistance of aluminum is low. Surface modifications are applied to overcome this deficiency. Among these, the micro-arc oxidation (MAO) method increases the corrosion resistance and attains excellent values in surface hardness. To better understand the RRA/MAO relationship, heat-treated (RRA) samples with four different parameters were coated with the MAO method. In this way, a ceramic oxide coating layer was created on the material surfaces. In order to determine the RRA parameter effect, the MAO process parameters are kept constant (anode voltage ([Formula: see text]): 500[Formula: see text]V, cathode voltage ([Formula: see text]): 300[Formula: see text]V, anode voltage open time ([Formula: see text]: 300[Formula: see text][Formula: see text]s, cathode voltage open time ([Formula: see text]): 200[Formula: see text][Formula: see text]s, frequency: 160 coating with Hz, and process time: 20[Formula: see text]min). Surface properties (coating thickness, surface roughness, surface arc duct’s structure, etc.), phase analysis (X-ray diffraction (XRD)) and microstructures (coating cross-section studies: distance-dependent hardness, coating/backing material interface character, coating porosity ratio) were examined. XRD analysis showed that the main phase of the coatings is [Formula: see text]-Al2O3. A coating layer of around 125[Formula: see text][Formula: see text]m was achieved with the growth rate of 6[Formula: see text][Formula: see text]m/min. Surface roughness was between 5.5[Formula: see text][Formula: see text]m and 8[Formula: see text][Formula: see text]m for different RRA parameters. RRA/MAO relation with the characterization made was detailed, and predictions were made for the surface properties of the material (hardness, corrosion resistance, wear, etc.).