Improvement of Fracture Toughness (K_1c) of 7075 Al Alloy by Cryorolling Process

Abstract:

The effects of cryorolling (Rolling at liquid nitrogen temperature) and optimum heat treatment (short annealing + ageing) on fracture toughness of 7075 Al alloy are reported in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic temperature and its mechanical, fracture toughness properties were studied. The microstructural characterization of the alloy was carried out by using Optical microscopy and Field emission scanning electron microscopy (FESEM). The cryo-rolled (CR) Al alloy after 70% thickness reduction exhibits ultrafine grain structure as observed from its FESEM micrographs. It is observed that the yield strength and fracture toughness of the CR material with 70% thickness reduction have increased by 108% and 73% respectively, compared to the starting material. The CR 7075 Al alloy shows improved fracture toughness and tensile strength due to high dislocation density, grain refinement, and ultrafine-grain (UFG) formation by multiple cryorolling passes. The CR samples were subjected to short annealing for 5 min at 190 0C, 170 0C and 150 0C followed by ageing at 160 0C, 140 0C and 120 0C for both 40% and 70% reduced samples. The combined effect of short annealing and ageing improves the fracture toughness, tensile strength, and ductility of cryorolled samples, which is due to precipitation hardening and subgrain coarsening mechanism respectively. The scanning electron microscopy (SEM) fractographs of the Al 7075 alloy samples reveals that starting bulk Al alloy specimens is fractured in a total ductile manner, consisting of well-developed dimples over the entire surface and dimple size got decreased continuously for cryorolled specimens at different percentage of thickness reduction (40% and 70%) as observed in the present work.

• Periodical: Materials Science Forum (Volume 683)
• Pages: 81-94
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.683.81
• Online since: May 2011
• Authors: P. Das, R. Jayaganthan, T. Chowdhury, Inderdeep Singh
• Keywords: 7075 Al-Alloy, Cryorolling, Fracture Toughness, Ultrafine Grained Alloy

References

[1] S. K. Panigrahi, R Jayaganthan, Materials Science Forum, Vols. 584-586, 2008, pp.734-740.

[2] Y. Wang, M. Chen, F. Zhou, E. Ma, Nature, Vol. 419 (2002), p.912–915.

[3] T.R. Lee, C.P. Chang, P.W. Kao, Mater. Sci. Eng. A, Vol. 408 (2005), p.131–135.

[4] N. Rangaraju, T. Raghuram, B.V. Krishna, K.P. Rao, P. Venugopal: Mater. Sci. Eng. A, Vol. 398 (2005), pp.246-251.

[5] Y.B. Lee, D.H. Shin, K.T. Park, W.J. Nam: Scripta Mater, Vol. 51 (2004), pp.355-359.

[6] T. Shanmugasundaram, B.S. Murty, V.S. Sarma: Scripta Mater, Vol. 54 (2006), p.2013-(2017).

[7] X. M. Li, M. J. Stranik: Materials Science and Technology, Vol. 17 (2001), pp.1324-1328.

[8] R.Z. Valiev, R.K. Islamgaliev, I.V. Alexandrov: Prog. Mater. Sci., Vol. 45 (2000), p.103–189.

[9] Jin-Feng LI, Zhuo-We P, Chao-Xing LI, Zhi-qiang J, Wen-Jing C, Zheng Z: Transactions of Nonferrous Metals Society of China, Vol. 18 (2008), p.755–762.

[10] Williams JC, Starke EA. Acta Materialia, Vol. 51(19) (2003), p.5775–5799.

[11] Woei-Shyan L, Wu-Chung S, Chi-Feng L, Chin-Jyi. W: Journal of Materials Processing Technology, Vol. 100 (2000), p.116–22.

[12] Steglich D, Brocks W, Heerens J, Pardoen T: Engineering Fracture Mechanics, Vol. 75(12)(2008), p.3692–706.

DOI: 10.1016/j.engfracmech.2007.04.008

[13] P. Das, R Jayaganthan, I.V. Singh: J Mater Design (2010), doi: 10. 1016/ j. matdes. 2010. 09. 026.

[14] R Jayaganthan, S. K. Panigrahi: Materials Science Forum, Vols. 584-586 (2008), pp.734-740.

[15] E647-08, Standard test method for measurement of fatigue crack growth rates, Annual Book of ASTM Standards, (2008).

[16] E399-08, Standard test method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic Materials, Annual Book of ASTM Standards, (2008).

DOI: 10.1520/e0399-06e01

[17] E 1820-08a, Standard test method for Measurement of Fracture Toughness, Annual Book of ASTM Standards, (2008).

[18] E8 / E8M-09. Standard Test Methods for Tension Testing of Metallic Materials, Annual Book of ASTM Standards, (2009).

[19] P. Nageshwara Rao, S.K. Panigrahi and R. Jayaganthan: Materials Science and Technology, Vol. 26, No. 3 (2010), pp.371-374.

[20] H. Somekawa , T. Mukai: Scripta Materialia, Vol. 53 (2005), p.1059–1064.

[21] H. Somekawa, T. Mukai: Journal of Alloys and Compounds, Vol. 417 (2006), p.209–213.

[22] N. Perez, Fracture Mechanics, Kluwer Academic Publishers, Newyork, (2004).

[23] E561-08, Standard test method for K-R curve determination. Annual Book of ASTM Standards, (2008).

[24] E. Gariboldi, D. Ripamonti, L. Signorelli, G. Vimercati, F. Casaro: Metallurgical Science and Technology, (2003), pp.143-155.

[25] S. K. Panigrahi, R. Jayaganthan: Materials Science and Engineering A, Vol. 480 (2008) p.299–305.

[26] Z.C. Wang, P.B. Prangnell: Materials Science and Engineering A, Vol. 328 (2002), p.87–97.