Tensile Properties and Fatigue Strength in High Humidity in Extruded 7075 Al Alloys with Different Aging Conditions

Abstract:

In the present study, the tensile and fatigue properties of extruded 7075 Al alloys subjected to re-solution treatment and then T6, T73 and retrogression-reaging (RRA) tempers were reassessed based upon the microstructural analyses by means of electron backscattering diffraction (EBSD) and X-ray diffraction (XRD). The microstructural analyses indicated that fibrous grains having orientations close to <111> and <001> were preferentially aligned in the extrusion direction and that re-solution treatment increased the fraction of <111> grains. Further the as-received T6 specimens had very high dislocation density as well as fine subgrains, while the re-solution treatment decreased dislocation density considerably and increased grain size. These characteristics explained tensile properties well, by taking into account the effect of precipitates formed by tempers. On the other hand, fatigue strength decreased prominently in all of the specimens, as the relative humidity (RH) was increased from 25% to 85%. T73 and RRA treatments which improve the resistance to stress corrosion cracking (SCC) in static loading were not effective in the humidity-enhanced deterioration in fatigue strength.

• Periodical: Advanced Materials Research (Volume 845)
• Pages: 292-296
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.845.292
• Online since: December 2013
• Authors: Y. Nakamura*, Norio Kawagoishi, K. Kariya
• Keywords: 7075 Al, Environmental Effect, Fatigue Properties, Microstructure, Tensile Properties

References

[1] I.J. Polmear, Light Alloys, 2nd Edtion, Edward Arnold, London, 1989, pp.1-104.

[2] N. Kawagoishi et al., Growth Mechanism of Shear Mode Fatigue Crack of Age-Hardened Al Alloy, Journal of JSMS, 60 (2011) 890-897.

DOI: 10.2472/jsms.60.890

[3] Y. Nakamura et al., Some Microstructural Aspects of Humidity-Enhanced Deterioration in 7075 T6 Alloy, Proceedings of ICF13, CD-ROM, S18-015, (2013).

[4] K. Kariya et al., Effects of Aging Structures and Humidity on Fatigue Properties of Age-Hardened Al Alloy, Journal of JSMS, 60 (2011) 1015-1022.

DOI: 10.2472/jsms.60.1015

[5] J. K. Park, Influence of Retrogression and Reaging Treatments on the Strength and Stress Corrosion Resistance of Aluminium Alloy 7075-T6, Mater Sci Eng, A103 (1988) 223-231.

DOI: 10.1016/0025-5416(88)90512-5

[6] M. Talianker and B. Cina, Retrogression and Reaging and the Role of Dislocations in the Stress Corrosion of 7000-Type Aluminum Alloys, Metal Trans A, 20A (1989) 1989-(2087).

DOI: 10.1007/bf02650294

[7] M. Raghavan, Microanalysis of Precipitate Free Zones (PFZ) in Al-Zn-Mg and Cu-Ni-Nb Alloys, Metal Trans A, 11A (1983) 993-999.

DOI: 10.1007/bf02654713