Effect of Cold Rolling and Annealing Temperature on the Recrystallization and Mechanical Properties of Al-4.7Zn-1.8Mg (wt. %) Alloy Fabricated by Squeeze Casting

Aluminium alloys are developed as airplane body due to their lighter weight compared to steel and good formability. Aluminium 7XXX series with Zn and Mg alloying elements is commonly used because its mechanical properties can be improved through a deformation process. A deformation process such as cold rolling may increase the hardness of an alloy through strain hardening. An annealing process following the deformation process will recover ductility through stress relief, recrystallization, and grain growth mechanisms. This research aimed to discover the effect of cold rolling and annealing temperature on the recrystallization and mechanical properties of Al-4.7Zn-1.8Mg (wt. %) alloy. The alloy was produced by a squeeze casting process. Homogenization was conducted at 400^oC for 4 hours followed by cold rolling with degrees of deformation of 5%, 10%, and 20%. The samples with 20% deformation were then annealed at 300^oC, 400^oC, and 500^oC for 2 h. The Vickers hardness test was performed on the cold-rolled and annealed samples to reveal the strain hardening effect and subsequent recrystallization process. The microstructure was observed using an optical microscope and a Scanning Electron Microscope (SEM). The results showed that the higher the deformation, the more elongated the grains. Deformation of 5, 10 and 20% led to grain shape ratios of 2.19, 3.19 and 4.59, respectively and increase in the hardness of the alloy from 69.5 VHN to 95.3, 100.1 and 105.4 VHN, respectively. Slip bands and cross slips were found only in the 20% deformed samples. The annealing process resulted in recovery at 300^oC, followed by recrystallization at 400^oC (d_grain ~290 ?m) and grain growth at 500^oC (d_grain ~434 ?m). Annealing temperatures of 300^oC, 400^oC and 500^oC decreased the hardness of the alloy from 105.4 VHN to 71.5, 96.8 and 95.3 VHN, respectively.

Al-Zn-Mg alloy; Annealing; Cold rolling; Grain growth; Recrystallization

The results of the investigation on Al-4.7Zn-1.8Mg (wt.%) alloy revealed that the homogenization process of as-cast alloy leads to a diffusion of the interdendritic phases into the ? matrix, followed by an increase in SDAS from 31.08 to 35.06 ?m, more globular dendrites, and a decrease in hardness from 94.4 to 69.52 VHN. Deformations of 5%, 10%, and 20% led to grain shape ratios of 2.19, 3.19, and 4.59 and an increase in the hardness of the alloy from 69.5 VHN to 95.3, 99.4, and 102.9 VHN, respectively. Slip bands and cross slips were found only in the 20% deformed samples. The annealing process resulted in recovery at 300^oC, followed by recrystallization at 400^oC (d_grain ~290 ?m) and grain growth at 500^oC (d_grain ~434 ?m). Annealing temperatures of 300^oC, 400^oC, and 500^oC decrease the hardness of the alloy from 102.9 VHN to 95.7, 94.9, and 94.1 VHN, respectively.

The authors are grateful for the provision of research funding through Hibah Publikasi Internasional Terindeks untuk Tugas Akhir (PITTA) 2017 from Universitas Indonesia.

Agrawal, L., Yadav, R., Sexena, A., 2012. Effect of Magnesium Content on the Mechanical Properties of Al-Zn-Mg Alloys. Int. J. Emerging. Tech., Volume 3, pp. 137–140

Lee, Y.S., Kim, W.K., Jo, D.A., Lim, C.Y., Kim, H.Y., 2014. Recrystallization Behavior of Cold Rolled Al?Zn?Mg?Cu. Trans. Nonfer. Met. Soc. Chi., Volume 24, pp. 2226–2231

Mohamed, A.B., Znaidi, A., Daghfas, O., Nasri, R., 2016. Evolution of Mechanical Behavior of Aluminium Alloy Al 7075 During Maturation Time. International Journal of Technology, Volume 7(6), pp. 1077–1085

Raghavan, V., 2010. Al-Mg-Zn (Aluminium-Magnesium-Zinc). J. Phase Equil. Diffusion, Volume 28, pp. 203–208

Rao, A.C.U., Vasu, V., Govindaraju, M., Sai, S.K.V., 2014. Influence of Cold Rolling on the Tensile Properties of Aluminium 7075 Alloy. Procedia Mat. Sci., Volume 5, pp. 86–95

Sofyan, B.T., Rahmalina, D., Siradj, E.S., Mochtadi, H., 2012. The Effect of Addition of Zn Alloy Elements to Balistic Composite Performance of Al-Zn-6Mg Matrix Strengthened by Silicon Carbide Particles (Pengaruh Penambahan Unsur Paduan Zn Terhadap Kinerja Balistik Komposit Matriks Al-Zn-6Mg Berpenguat Partikel Silicon Karbida). In: Prosiding Seminar Nasional InSINas, pp. HK141–HK145 (in Bahasa)

Wang, B., Chen, X., Pan, F., Mao, J., Fang, Y., 2015. Effects of Cold Rolling and Heat Treatment on Microstructure and Mechanical Properties of AA5052 Aluminium Alloy. Trans. Nonfer. Met. Soc. Chi., Volume 25, pp. 2481–2489

Ying, D., Xu, G., Yin, Z., Lei, X., Huang, J., 2013. Effects of Sc and Zr Microalloying Additions on the Recrystallization Texture and Mechanism of Al-Zn-Mg Alloys. J. Alloy Comp., Volume 580, pp. 412–426

Yvind, R., Nijs, O., Sjölander, E., Holmedal, B., Ekström, H.E., Nes, E., 2006. Strengthening Mechanisms in Solid Solution. Met. Mat. Trans., Volume 37A, pp. 1999–2006

Zolotorevsky, V.S., Nikolai, A.B., Glazoff, M.V., 2007. Casting Aluminium Alloys, Moscow. Elsevier