Effect of aging on fracture toughness and stress corrosion cracking resistance of forged 7475 aluminum alloy

Abstract

The effects of two-stage aging and retrogression and reaging heat treatment on the fracture toughness and stress corrosion cracking resistance of 7475 alloy were studied. The fracture toughness, conductivity and strength of samples of nine groups under duplex aging conditions and three retrogression and reaging heat treatments were also measured. Incorporating the microstructure and property, we found that when the condition of the first order aging kept identical, the fracture toughness and stress corrosion cracking resistance increase with aging time and the second aging temperature. The optimal treatment conditions are (115°C×7h+185°C×13h) among all tested two-stage aging treatments. Although the 7475 alloy treated by RRA method shows the highest strength and its stress corrosion cracking resistance after twenty minutes retrogression can also reach the same level as those by the optimal treatment of (115°C×7h+185°CsX13h), the fracture toughness is even low.

Keywords

7475 alloy / two-stage aging / heat treatment / RRA treatment fracture toughness / stress corrosion

References

[1] Chen Y., Zheng Z., Li Q. Effects of Aging on Microstructure and Properties of 7475 Alloy[J]. Light Alloy Fabrication Technology, 2001, 29(5): 40-45.

[2] Pan Z., Li W., Ma Z., . Development and Present States of Researching High Strength Aluminum Alloys[J]. Aluminum Fabrication, 2001, 24(4): 39-41.

[3] Megson T. Aircraft Structures[M], 1999. Woburn,MA,USA: Butterworth Heinemann.

[4] Fielding J. Introduction to Aircraft Design[M], 1999. Cambridge,UK: Cambridge University Press.

[5] Ashby M., Jones D. Engineering Materials[M], 1996. Woburn,MA,USA: ButterworthHeinemann.

[6] Polmear I. Light Alloys[M], 1995. London,UK: Arnold.

[7] Luquan Zhang.Two Stage Aging of 7xxx Type Aluminum Alloy[J]. Light Alloy Fabrication Technology,1987(5):16–21

[8] China B. Reducing the Susceptibility of Alloy, Particular Aluminum Alloys to Stress Corrosion Cracking[P]. US.Pat: 3856584, 1974

[9] PAark J. K., Ardell A. J. Effect of Retrogression and Reaging Treatments on the Microstructure of Al-7075-T65[J]. Metallurgical Transactions A, 1984, 15A: 1531-1543.

[10] Ohnishi T., Ibaraki Y., Ito T. Improvement of Fracture Toughness in AA7475 by the Retrogression and Reaging Process[J]. Materials Transactions JIM, 1989, 30: 601-607.

[11] Z Lin, W Jiang, S Yang,et al.Proc.2 ^nd Int.Conf.on Aluminium Alloys-their Physical and Mechanial Properties[C]. Beijing,China,October 1990,Northeast University of Technology,480–485

[12] W U Islam, W Wallace.Retrogression and Reaging Response of 7475 Aluminum Alloy[J]. Metals Technology,1983(10):386–392

[13] J S Robinson. Influence of Retrogression and Reaging on Fracture Toughness of 7010 Aluminum Alloy[J]. Materials Science and Technology,2003(19):1697

[14] Standard Test Method for Electromagnetic(Eddy current)Measurements of Electrical Conductivity[S]. ASTM Standard E1004-91,ASTM, Philadephia,PA,USA,1992

[15] Tsai T. C., Chung T. H. Role of Grain Size on the Stress Corrosion Cracking of 7475 Aluminum alloy[J]. Materials Science and Engineering, 1997, A225: 139-141.

[16] Zheng Z., Li H., Li W., . Research on Grain Refi nement of Aluminum Alloys[J]. Journal of Xiangtan Mining Institute, 2003, 18(2): 41-43.

[17] Song R. G. Grain Boundary Segregation and Hudrogen-induced Fracture in 7050 Aluminum Alloy[J]. Acta Mater., 1996, 44: 3241

[18] Zheng Z., Li H., Mo Z. Retrogression and Reaging Treatment of a 7055 Type Aluminum Alloy[J]. Trans. Nonferrous Met. Soc. China, 2001, 11(5): 771-776.

[19] Kanno M., Araki I., Cui Q. Precipitation Behavior of 7000 Alloys During Retrogression and Reaging Treatment [J]. Mater. Sci. and Technol., 1994, 10(7): 599