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Bhuiyan M.S.,Nagaoka University of Technology | Mutoh Y.,Nagaoka University of Technology | Murai T.,Sankyo Tateyama Aluminum Corporation | Iwakami S.,Sankyo Tateyama Aluminum Corporation
Engineering Fracture Mechanics | Year: 2010

The corrosion fatigue behavior of extruded AZ80-T5 magnesium alloy has been investigated in three different environments: (1) a low humidity environment (35-40% relative humidity), (2) a high-humidity environment (80% relative humidity), and (3) a 5. wt.% NaCl environment. Fatigue tests were conducted under axial loading at a stress ratio of -1 and at a frequency of 20. Hz. It was found that in both the high-humidity environment and in the 5 wt.% NaCl environment the fatigue strength was reduced relative to the low humidity environment, especially in the NaCl environment: the reduction rates of fatigue limit under high humidity and NaCl environments were 18%, and 78%, respectively. The reduction of fatigue strength under the corrosive environments was attributed to the pit formation and growth. At low stress amplitudes, multiple pits were formed and coalesced to form a large pit under NaCl environment. A fatigue crack nucleated when the pit grew to the critical size. © 2010 Elsevier Ltd. Source


Bhuiyan M.S.,Nagaoka University of Technology | Ostuka Y.,Nagaoka University of Technology | Mutoh Y.,Nagaoka University of Technology | Murai T.,Sankyo Tateyama Aluminum Corporation | Iwakami S.,Sankyo Tateyama Aluminum Corporation
Materials Science and Engineering A | Year: 2010

The corrosion fatigue behavior of conversion coated extruded AZ61 magnesium alloy has been investigated under two corrosive environments: (a) high humidity environment and (b) 5. wt.% NaCl environment. It was found that under a low humidity environment without corrosive attack, the fatigue limit of coated material was almost the same as that of the bulk material under the same environment: the reduction rate of fatigue limit was about 3%. Under corrosive environments, i.e., under high humidity and 5. wt.% NaCl environment, the application of conversion coating improved fatigue limit compared to that of bulk material under the same environment. However, when compared to the fatigue limit of bulk material under low humidity environment, the fatigue limit of coated specimen was reduced: the reduction rates were about 11% and 63% under high humidity environment and 5. wt.% NaCl environment, respectively. Fracture surface observations of the coated specimens under high humidity environment showed no existence of corrosion pit in the crack nucleation region, which indicating that the conversion coating not perfectly but significantly protects the substrate material from the attack of high humidity environment, whereas under 5. wt.% NaCl environment corrosion pits were observed at the crack nucleation region, which indicates that the conversion coating could not protect the substrate material from the attack of 5. wt.% NaCl environment. Therefore, it is suggested that the conversion coating can work to a certain degree of protection from corrosive attack of high humid environment but not enough for perfect protection from the attack of 5. wt.% NaCl environment. © 2010 Elsevier B.V. Source

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