• Vol 8, No 7 (2017)
  • Metalurgy and Material Engineering

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

Rachman Kurnia, Bondan Tiara Sofyan


Cite this article as:
Kurnia, R., Sofyan, B.T., 2017. 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. International Journal of Technology, Volume 8(7), pp. 1329-1335
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Rachman Kurnia - Department of Metallurgy and Materials Engineering, Universitas Indonesia
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Bondan Tiara Sofyan - Department of Metallurgy and Materials Engineering, Universitas Indonesia
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Abstract
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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 400oC 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 300oC, 400oC, and 500oC 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 300oC, followed by recrystallization at 400oC (dgrain ~290 ?m) and grain growth at 500oC (dgrain ~434 ?m). Annealing temperatures of 300oC, 400oC and 500oC 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

Conclusion

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 300oC, followed by recrystallization at 400oC (dgrain ~290 ?m) and grain growth at 500oC (dgrain ~434 ?m). Annealing temperatures of 300oC, 400oC, and 500oC decrease the hardness of the alloy from 102.9 VHN to 95.7, 94.9, and 94.1 VHN, respectively.

Acknowledgement

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

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