Fatigue life of micro-arc oxidation coated AA2024-T3 and AA7075-T6 alloys

• Published in: International journal of fatigue Vol. 124; pp. 493 - 502
• Main Authors: Dai, Weibing, Liu, Zhenhua, Li, Changyou, He, David, Jia, Dawei, Zhang, Yimin, Tan, Zhi
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.07.2019; Elsevier BV
• Subjects: Alloys; Aluminum base alloys; Ceramic coatings; Copper; Fatigue; Fatigue cracks; Fatigue life; Fatigue tests; Materials fatigue; Metal fatigue; Microcracks; Microscopy; Microstructure; Morphology; Oxidation; Oxidation time; Porosity; Residual stress; Scanning electron microscopy; Scanning microscopy; Substrates; Thin coating; X-ray diffraction; Zinc coatings; Fatigue; Thin coating; Microstructure; Oxidation time; Residual stress
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2019.03.028

•Pores adjacent to the interface were detrimental to fatigue life.•Distribution of Cu and Zn within MAO coatings affected the property of residual stress.•The residual stress changed fatigue crack propagation path.•Fatigue life first increased and then decreased with prolonging the oxidation time. Two types of aluminum (Al) alloys, namely 2024-T3 and 7075-T6, were treated by micro-arc oxidation (MAO). Microstructure of as-fabricated ceramic coatings was investigated. Furthermore, the effect of MAO time on fatigue life of the coated samples with thin coating was systematically explored. Morphologies of the coating, second phase particles, and distribution of copper (Cu) and Zinc (Zn) in the coating were observed by scanning electron microscopy, confocal laser scanning microscopy, and energy dispersive spectrometry. Residual stress and phase compositions were analyzed by X-ray diffraction. More Cu in 2024-T3 Al alloy promoted formation of the coating; however, surface porosity of the coating was high. Residual stress induced in the coating deposited on AA2024 was compressive in nature. In contrast, the residual stress in the coating prepared on AA7075 was tensile due to the high content of Zn in the substrate. The results of fatigue test showed that fatigue life of the coated AA2024 increased; however, the MAO treatment was detrimental to fatigue performance of the AA7075 compared to uncoated samples. With prolonging oxidation time, the fatigue life of the coated samples first increased and then decreased. The changes of fatigue life were attributed to the residual stress, coating defects including micro-pores and micro-cracks, and second phase particles in the Al alloy substrate.