Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Effect of Two-Step Aging Treatment on the Stress Corossion Cracking Resistance of 7050 Al Alloy

7050 Al합금의 응력부식저항성에 미치는 2단 시효처리의 영향

  • Choe, Jung-Hwan (Dept.of Metallurgical Engineering, Busan National University) ;
  • Kim, Jong-Gi (Hyundai Mortor) ;
  • Kim, Heon-Gyu (Dept.of Metallurgical Engineering, Busan National University) ;
  • Lee, Sang-Rae (Dept.of Metallurgical Engineering, Busan National University) ;
  • Kim, In-Bae (Dept.of Metallurgical Engineering, Busan National University)
  • Published : 1999.07.01
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Abstract

Effects of two-step aging treatment on the stress corrosion cracking(SCC) resistance of 7050 Al alloy were investigated by transmission electron microscopy, electrical conductivity measurement and stress corrosion facter(SCF) evaluation. It was found that η', principal hardening phase, transformed to η during over aging above maximum hardness, and SCC resistance was improved by increasing of the size and interspacing of η particles in matrix and grain boundary. The electrical conductivity increased with aging time, but SCF decreased due to the decrease of yield strength. This results mean increase of SCC resistance The optimum two-step aging condition in forged 7050 Al alloy was to be first aged at $120^{\circ}C$ for 6h and then finally aged at $175^{\circ}C$ for 12h.

7050 Al합금의 응력부식저항성에 미치는 2단 시효처리의 영향을 미세조직관찰, 전기전도도시험 및 SCF값을 평가함으로써 조사하였다. 최대 경도 이상 과시효에 의해 주 강화상인 η'상이 η상으로 변태되었고, 입내 및 입계에 존재하는 η상의 크기와 간격이 커졌으며 그 결과 응력부식저항성이 증대되었다. 2차 시효시간의 증가에 따라 전기전도도값은 증가되었으나 항복강도의 감소로 인하여 SCF값은 감소되었는데, 이러한 결과는 응력부식저항성의 증가를 의미한다. AMS 4107규격을 기준으로 하였을 때 7050 Al합금 단조재의 적정시효조건은 1차시효가 12$0^{\circ}C$에서 6시간, 2차시효는 $175^{\circ}C$에서 12시간이었다.

Keywords

References

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