Effects of Cu Addition on the Precipitation Process of Al-9Zn-4Mg-xCu (wt. %) Alloys at 130°C

Abstract:

Aluminium is a light-weight material and possesses high corrosion resistance, so that it is widely used in manufacturing industries. The Al-Zn series have the highest strength compared to other aluminium alloys. To further increase the strength of Al-Zn alloys, Mg and Cu are added and age hardening treatment is applied. This research studied the precipitation process in Al-9Zn-4Mg (wt. %) alloys with Cu content of 0, 1, 3 and 5 wt.%. The alloys were produced through investment casting taking the shape of turbine impeller. The samples were solution treated at 460 °C for 2 hours and then aged at 130 °C. The characterization included hardness testing to observe response of age hardening, microstructural observation and Differential Scanning Calorimetry (DSC) testing. Microstructural observation was conducted by optical microscope and Scanning Electron Microscope (SEM) which was combined with Energy Dispersive Spectroscopy (EDS). The results showed that addition of Cu initially decreased the hardness during early ageing (2 hours) due to segregation of Cu-V complexes toward the grain boundaries which then decreased the hardness and enlarged the grain boundary phases. However, the peak hardness of the alloys was not affected by the increase in Cu content. due to high concentration of Zn and Mg. Exothermic reactions of formation of GP zones, η", η' and η (MgZn₂) were found during precipitation process while endothermic reaction were observed due to dissolution of the phases. Presence of MgZn₂ and Al₇Cu₂Fe second phases were observed in grain boundaries.

• Periodical: Applied Mechanics and Materials (Volume 835)
• Pages: 222-229
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.835.222
• Online since: May 2016
• Authors: Bondan Tiara Sofyan*, Immalatul Husna, Muhammad Syahid
• Keywords: Ageing, Al-Zn, Cu, Grain Boundary, MgZn₂

References

[1] I.J. Polmear, Light alloys: Metallurgy of the light metals. 3rd. ed., Arnold, London, (1995).

[2] L. Hadjadj, R. Amira, The effect of Cu addition on the precipitation and redissolution in Al-Zn-Mg alloy by the differential dilatometry. J. Alloys Comp. 484(1-2) (2009) 891-895.

DOI: 10.1016/j.jallcom.2009.05.082

[3] N.Q. Chinh, J. Lendvai, D.H. Ping, K. Hono, The effect of Cu on mechanical and precipitation properties of Al-Zn-Mg alloys. J. Alloys Comp. 378(1-2) (2004) 52-60.

DOI: 10.1016/j.jallcom.2003.11.175

[4] X. Fan, D. Jiang, Q. Meng, B. Zhang, T. Wang, Evolution of eutectic structures in Al-Zn-Mg-Cu alloys during heat treatment. Trans. Nonfe. Met. Soc. China, 16 (2006) 577-581.

DOI: 10.1016/s1003-6326(06)60101-5

[5] S. Fujikawa, T. Hara, A. Ishida, K. Hirano, A calorimetric study of precipitation process in Al-Zn-Mg-Cu alloys, Thermochim. Acta 85 (1985) 171–174.

DOI: 10.1016/0040-6031(85)85557-x

[6] S.K. Caraher, I.J. Polmear, and S.P. Ringer, Effects of Cu and Ag on precipitation in Al–4Zn–3Mg (wt. %). In Proc. 6th Intl. Conf. Aluminium Alloys (ICAA6), July 5–10, 1998, T. Sato, S. Kumai, T. Kobayashi, and Y. Murakami, eds. Toyohashi, Japan, Japan Institute for Light Metals, Tokyo, 2 (1998).

[7] I.J. Polmear, The ageing characteristics of ternary aluminium–zinc–magnesium alloys. J. Inst. Met. 86 (1957–58) 113–121.

[8] I.J. Polmear, The upper temperature limit of stability of GP zones in ternary aluminium–zinc–magnesium alloys. J. Inst. Met. 87 (1958–59) 24–25.

[9] J.T. Vietz, K.R. Sargant, and I.J. Polmear, The influence of small additions of silver on the ageing of aluminium alloys: Further observations on Al–Zn–Mg alloys. J. Inst. Met. 92 (1963–64) 327–333.

[10] I.J. Polmear, The ageing characteristics of complex Al–Zn–Mg alloys: Distinctive effects of Cu and Ag on the ageing mechanism. J. Inst. Met. 89 (1960) 51–59.

[11] A. Syakuura, B.T. Sofyan, S.P. Ringer, Mechanical properties and precipitation hardening alloys of Al-Zn-Mg with Cu content variations during aging at a temperature of 120 °C, Magazine of Science and Technology, Metallurgy, 27(2) (2012) 85-94.

DOI: 10.14203/metalurgi.v27i2.143

[12] K.N.Y. Fujikawa, T. Sakurai (Ed. ). Frontiers in Materials Research, Springer, Berlin, (2008).

[13] S.P. Ringer, K. Hono, Microstructural Evolution and Age Hardening in Aluminium Alloys: Atom Probe Field-Ion Microscopy and Transmission Electron Microscopy Studies, Mat. Charact. 44 (2000) 101–131.

DOI: 10.1016/s1044-5803(99)00051-0

[14] M. Li, Y. Yang, Z. Feng, B. Huang, X. Luo, J. Luo, J. Ru, Precipitation sequence of η phase along low-angle grain boundaries in Al-Zn-Mg-Cu alloy during artificial aging. J. Trans. Nonfe. Met. Soc. China. 24 (2014) 2061-(2066).

DOI: 10.1016/s1003-6326(14)63312-4

[15] Y. Liao, X. Han, M. Zeng, M. Jin, Influence of Cu on microstructure and tensile properties of 7xx series aluminum alloy. J. Mat. Des. 66 (2015) 581-586.

DOI: 10.1016/j.matdes.2014.05.003

[16] G. Sha, L. Yao, X. Liao, S.P. Ringer, Z.C. Duan, T.G. Langdon, Segregation of solute elements at grain boundaries in an ultrafine grained Al-Zn-Mg-Cu alloy. J. Ultramicrosc. 111 (2011) 500-505.

DOI: 10.1016/j.ultramic.2010.11.013

[17] G. Sha, A. Cerezo, Early-stage precipitation in Al-Zn-Mg-Cu alloy (7050). Acta Mat. 52 (2004) 4503-4516.

DOI: 10.1016/j.actamat.2004.06.025

[18] E.A. Brandes, G.B. Brook, Smithells Metals Reference Book 7th ed. The Bath Press, Great Britanian, (1992).

[19] K.G. Krishna, K. Sivaprasad, K. Venkateswarlu, K.C.H. Kumar, Microstructural evolution and aging behavior of cryorolled Al-4Zn-2Mg Alloy. J. Mat. Sci. Eng. 535 (2012) 129-135.

DOI: 10.1016/j.msea.2011.12.052

[20] W.F. Miao, D.E. Laughlin, A differential scanning calorimetry study of aluminum alloy 6111 with different pre-aging treatment. J. Mat. Sci. Let. 19 (2000) 201-203.