Restricted accessResearch articleFirst published online 2022-12
Investigating the effects of pre-deformation and aging conditions on mechanical properties and SCC resistance of aluminium alloy 7075 via slow strain rate testing and electrochemical polarisation
In this study, the effects of pre-deformation on mechanical properties and stress corrosion cracking behaviour of 7075 alloy was investigated with SSRT and electrochemical polarization. The 10% pre-deformation substantially improves the SCC resistance of the 7075 alloys. The strain induced dislocations act as diffusion shortcuts and result in enhanced precipitation and early appearance of GBPs in the naturally aged 7075-T3. For artificial aging, pre-deformation causes rapid over-aging as larger precipitates are found in both matrix and GBs of the 7075-T8. The substitution of Cu for Zn in the GBPs and the larger GBPs acting as hydrogen traps are possible explanations for the improved SCC resistance of 7075-T8. Further improvements in SCC resistance can be found in the RRA treated 7075 alloys, while a more ductile behaviour can be seen in the pre-deformed 7075 alloy. Additionally, results of electrochemical testing are in high correlation with the SSRT results.
SchnattererCZanderD.Influence of heat treatments on the stress corrosion cracking susceptibility of 7075 aluminum wires in NaCl solutions. Mater Corros. 2016; 67 (11): 1164–1172.
2.
GoswamiRLynchSHolroydNJH. Evolution of grain boundary precipitates in Al 7075 upon aging and correlation with stress corrosion cracking behavior. Metall Mater Trans A. 2013; 44 (3): 1268–1278.
3.
MagajiNMayrhoferRKrögerB. Comparison of test methods used to analyze stress corrosion cracking of differently tempered 7xxx alloys. Mater Corros. 2019; 70 (7): 1192–1204.
4.
ZaidHRHatabAMIbrahimAMA.Properties enhancement of Al-Zn-Mg alloy by retrogression and re-aging heat treatment. J Min Metall Sect B. 2011; 47 (1): 31–35.
5.
OñoroJ.The stress corrosion cracking behaviour of heat-treated Al-Zn-Mg-Cu alloy in modified salt spray fog testing. Mater Corros. 2009: 125–129.
6.
LynchSP.Mechanistic and fractographic aspects of stress-corrosion cracking (SCC). In: RajaV. S.ShojiT., editors. Stress corrosion cracking: theory and practice. Sawston, Cambridge: Woodhead Publishing; 2011. p. 3–89.
7.
CinaBM.1974.
8.
PoulosePKMorralJEMcEvilyAJ.Stress corrosion crack velocity and grain boundary precipitates in an Al-Zn-Mg alloy. Metall Trans. 1974; 5 (6): 1393–1400.
9.
PuiggaliMZielinskiAOliveJM. Effect of microstructure on stress corrosion cracking of an Al-Zn-Mg-Cu alloy. Corros Sci. 1998; 40 (4-5): 805–819.
10.
RedaYAbdel-KarimRElmahallawiI.Improvements in mechanical and stress corrosion cracking properties in Al-alloy 7075 via retrogression and reaging. Mater Sci Eng A. 2008; 485 (1-2): 468–475.
11.
KnightSPBirbilisNMuddleBC. Correlations between intergranular stress corrosion cracking, grain-boundary microchemistry, and grain-boundary electrochemistry for Al-Zn-Mg-Cu alloys. Corros Sci. 2010; 52 (12): 4073–4080.
12.
ChenSYChenKHPengGS. Effect of quenching rate on microstructure and stress corrosion cracking of 7085 aluminum alloy. Trans Nonferrous Met Soc China. 2012; 22 (1): 47–52.
13.
ChenSChenKDongP. Effect of recrystallization and heat treatment on strength and SCC of an Al-Zn-Mg-Cu alloy. J Alloys Compd. 2013; 581: 705–709.
14.
SunXYZhangBLinHQ. Correlations between stress corrosion cracking susceptibility and grain boundary microstructures for an Al-Zn-Mg alloy. Corros Sci. 2013; 77: 103–112.
15.
RoutPKGhoshMMGhoshKS.Effect of solution pH on electrochemical and stress corrosion cracking behaviour of a 7150 Al-Zn-Mg-Cu alloy. Mater Sci Eng A. 2014; 604: 156–165.
16.
CsanádyAMartonD.Stress corrosion behaviour of Al-Zn-Mg alloys based upon microchemical surface reactions. J Mater Sci. 1979; 14 (10): 2289–2295.
17.
ArnottDrBaxterWJRouzeSR.Oxide film rupture, reanodization, and stress corrosion cracking in aluminum. J Electrochem Soc. 1982; 129 (12): 2660–2665.
18.
ParkJKArdellAJ.Microchemical analysis of precipitate free zones in 7075-A1 in the T6, T7 and RRA tempers. Acta Metall Mater. 1991; 39 (4): 591–598.
19.
LinJCLiaoHLJehngWD. Effect of heat treatments on the tensile strength and SCC-resistance of AA7050 in an alkaline saline solution. Corros Sci. 2006; 48 (10): 3139–3156.
20.
VasudevanAKSadanandaK.Role of slip mode on stress corrosion cracking behavior. Metall Mater Trans A. 2011; 42 (2): 405–414.
21.
TsaiTCChuangTH.Role of grain size on the stress corrosion cracking of 7475 aluminum alloys. Mater Sci Eng A. 1997; 225 (1-2): 135–144.
22.
WuLMWangWHHsuYF. Effects of microstructure on the mechanical properties and stress corrosion cracking of an Al-Zn-Mg-Sc-Zr alloy by various temper treatments. Mater Trans. 2007; 48 (3): 600–609.
23.
NajjarDMagninTWarnerTJ.Influence of critical surface defects and localized competition between anodic dissolution and hydrogen effects during stress corrosion cracking of a 7050 aluminium alloy. Mater Sci Eng A. 1997; 238 (2): 293–302.
24.
ParkJKArdellA.Microstructures of the commercial 7075 Al alloy in the T651 and T7 tempers. Metall Trans A. 1983; 14: 1957–1965.
25.
VianaFPintoAMPSantosHMC. Retrogression and re-ageing of 7075 aluminium alloy: microstructural characterization. J Mater Process Technol. 1999; 92-93: 54–59.
26.
ScamansGM.Hydrogen bubbles in embrittled Al-Zn-Mg alloys. J Mater Sci. 1978; 13 (1): 27–36.
27.
RajanKWallaceWBeddoesJC.Microstructural study of a high-strength stress-corrosion resistant 7075 aluminium alloy. J Mater Sci. 1982; 17 (10): 2817–2824.
28.
FerrerCPKoulMGConnollyBJ. Improvements in strength and stress corrosion cracking properties in aluminum alloy 7075 via low-temperature retrogression and re-aging heat treatments. Corrosion. 2003; 59 (6): 520–528.
29.
BaydoganMCimenogluHSabri KayaliE. Improved resistance to stress-corrosion-cracking failures via optimized retrogression and reaging of 7075-T6 aluminum sheets. Metall Mater Trans A. 2008; 39 (10): 2470–2476.
30.
LiHQingzhongMWangZ. Simultaneously enhancing the tensile properties and intergranular corrosion resistance of Al-Mg-Si-Cu alloys by a thermo-mechanical treatment. Mater Sci Eng A. 2014; 617: 165–174.
31.
HouK-HHuL-YChangC-W.Investigating the effects of pre-deformation and aging conditions on localised corrosion behaviour of aluminium alloy 6061 via electrochemical polarisation. Corros Eng Sci Technol. 2021; 56 (8): 796–807.
32.
LöfflerHKovácsILendvaiJ.Decomposition processes in Al-Zn-Mg alloys. J Mater Sci. 1983; 18 (8): 2215–2240.
33.
DeschampsALivetFBréchetY.Influence of predeformation on ageing in an Al–Zn–Mg alloy – I. Microstructure evolution and mechanical properties. Acta Mater. 1998; 47 (1): 281–292.
34.
UralK.A study of optimization of heat-treatment conditions in retrogressions and reageing treatment of 7075-T6 aluminium alloy. J Mater Sci Lett. 1994; 13 (5): 383–385.
35.
ZhangWFrankelGS.Transitions between pitting and intergranular corrosion in AA2024. Electrochim Acta. 2003; 48 (9): 1193–1210.
36.
Ul-HamidA.Electrochemical behaviour of Al alloys in aerated and deaerated NaCl solution. Corros Prev Control. 2001; 48 (4): 151–159.
37.
HuangTSFrankelGS.Effects of temper and potential on localized corrosion kinetics of aluminum alloy 7075. Corrosion. 2007; 63 (8): 731–743.
38.
El-AmoushAS.Intergranular corrosion behavior of the 7075-T6 aluminum alloy under different annealing conditions. Mater Chem Phys. 2011; 126 (3): 607–613.
39.
MaitraSEnglishGC.Mechanism of localized corrosion of 7075 alloy plate. Metall Trans A. 1981; 12 (3): 535–541.
