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 di®erent times (30 and 90 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 modi¯cations are applied to overcome this de¯ciency. Among these, the micro-arc oxidation (MAO) method increases the corrosion resistance and attains excellent values in surface hardness. To better understand the RRA/MAOrelationship, heat-treated (RRA) samples with four di®erent 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 e®ect, the MAO process parameters are kept constant (anode voltage (Va): 500V, cathode voltage (Vk): 300 V, anode voltage open time (ta Þ: 300 s, cathode voltage open time (tk): 200 s, frequency: 160 coating with Hz, and process time: 20 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 -Al2O3. A coating layer of around 125 m was achieved with the growth rate of 6 m/min. Surface roughness was between 5.5 m and 8 m for di®erent 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.).