CaO 첨가 AZ31 압출재의 개량된 미세조직이 인장, 고주기 피로 및 피로 균열 전파 특성에 미치는 영향

• Published in: 대한금속·재료학회지, 59(6) Vol. 59; no. 6; pp. 365 - 373
• Main Authors: 김영균, Young-kyun Kim, 김민종, Min-jong Kim, 황유진, Yu-jin Hwang, 김세광, Shae. K. Kim, 임현규, Hyun-kyu Lim, 이기안, Kee-ahn Lee
• Format: Journal Article
• Language: Korean
• Published: 대한금속재료학회 05.06.2021; 대한금속·재료학회
• Subjects: AZ31; CaO; fatigue crack propagation; high cycle fatigue; magnesium alloy; microstructure; tensile; 재료공학
• ISSN: 1738-8228; 2288-8241

The effect of tailored microstructures in 0.5 wt% CaO added AZ31 on tensile, high-cycle fatigue, and fatigue crack growth properties was examined. By adding CaO, the average grain size (AGS) was significantly reduced from 4.25±2.32 μm (conventional AZ31) to 2.42±1.60 μm (CaO-AZ31). The fineprecipitates of CaO-AZ31 were more evenly distributed and their fraction was higher than those of conventional AZ31. The fine-precipitates were identified as Al 8 Mn 4 Ca and (Mg, Al) 2 Ca in CaO-AZ31, meanwhile, were identified as Al 8 Mn 5 and Mg 17 Al 11 in conventional AZ31. The tensile test results showed that the yield strengths of CaO-AZ31 and conventional AZ31 were 238.0 MPa and 206.7 MPa, respectively. The elongation-to-failure also increased when CaO was added. The improved tensile properties of CaO-AZ31 could be explained by grain refinement and precipitation hardening. The high-cycle fatigue limit also increased about 15% with added CaO. The fatigue limits as a function of the tensile strengths of CaO-AZ31 and conventional AZ31 were 0.508 and 0.457, respectively. The origin of the improved fatigue resistance was attributed to inhibition of the formation of DTs, which acted as the fatigue crack source, in CaO-AZ31. In contrast, the fatigue crack growth property did not change when CaO was added. Based on the above findings, the relationships between microstructure, mechanical properties and deformation mechanisms are also discussed. (Received February 23 2021; Accepted March 30, 2021)