Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

Abstract

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.40.1 Adm 2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 μm. Residual stresses attributed to γ-Al 2 O 3 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin 2 ψ method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 66720 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.

A review of recent work on discharge characteristics during plasma electrolytic oxidation of various metals

“…In fact, there have been several reports [102][103][104][105][106] of high measured residual stress levels (>∼400 MPa) in PEO coatings, although there are also very wide variations in the results. However, these were all obtained using measured shifts of X-ray diffraction peaks.…”

Plasma Electrolytic Oxidation of High-Strength Aluminium Alloys—Substrate Effect on Wear and Corrosion Performance

“…Nevertheless, all these phases exhibit a significantly higher hardness compared to the substrate [12][13][14] and also compared to oxide coatings produced by anodising or hard-anodising. The high hardness, residual compressive stresses in the oxide coating [15], and the compact microstructure of the oxide coatings produced by PEO lead to a high wear resistance [12,16,17]. Since the oxide is chemically stable and its morphology is often compact, corrosion resistance is also enhanced [18][19][20].…”

Influence of Ultrasound on the Characteristics of CaP Coatings Generated Via the Micro-arc Oxidation Process in Relation to Biomedical Engineering

“…22,45,55 It was found that the use of ultrasound on aluminum alloy increased the thickness of MAO coatings and favored phase transformation from γ-Al 2 O 3 to α-Al 2 O 3 . 54 In the case of Ti-6Al-4 V, it was noted that the US influenced the morphology, phase composition, wear resistance, and corrosion properties of MAO coatings. 56 This is related not only to the use of ultrasound but also to the electrolyte components and process parameters.…”