Natural-ageing-enhanced precipitation near grain boundaries in high-strength aluminum alloy

doi:10.1016/j.jmst.2019.11.035

Abstract

Abstract:

Artificial ageing above 165 °C directly after quenching induces the formation of ~50 nm wide precipitate-free zone (PFZ) and ~100 nm wide precipitate-sparse zone (PSZ) consisting of coarse precipitates with a gradient in size and density toward the grain center in a commercial Al-Zn-Mg-Cu alloy. With the grain size decreasing, the fraction of PFZ and PSZ in a grain becomes larger and could even occupy the entire volume of the grain. This undesirable microstructure near the grain boundary is mitigated substantially by natural pre-ageing, leading to an exceptional enhancement of the age hardening potential at elevated temperatures. Natural ageing could fundamentally alter the precipitation near grain boundary, and is a promising method to optimize the precipitation hardening in high strength aluminum alloys with unconventionally small grains.

Key words: Precipitation hardening, Grain boundary, Natural ageing, Grain size, Aluminum alloy

Peipei Ma, Chunhui Liu, Qiuyu Chen, Qing Wang, Lihua Zhan, Jianjun Li. Natural-ageing-enhanced precipitation near grain boundaries in high-strength aluminum alloy[J]. J. Mater. Sci. Technol., 2020, 46: 107-113.

Figures/Tables 6

Fig. 1. (a) Vickers microhardness versus aging time at different ageing temperatures in Al-Zn-Mg-Cu alloy with and without pre-NA; (b) the maximum hardness acquired at various ageing temperatures in samples with and without NA.

Fig. 2. (a) The maximum yield strength acquired at various ageing temperatures in samples with and without NA; (b) engineering stress-strain curves of the samples aged at 165 °C and 180 °C.

Fig. 3. HAADF-STEM images of plate-like hardening precipitates in the grain interior of samples peak-aged at 120 °C (a, d), 165 °C (b, e) and 180 °C (c, f). The upper images are for directly aged samples (a-c) while the lower ones for naturally pre-aged samples (d-f). The inset in (a) is the selected area diffraction pattern (SADP). (g) High-resolution HAADF-STEM images of typical precipitates varying in internal structures in the samples peak-aged at 120 °C, 165 °C and 180 °C, respectively. The bright dots correspond to Zn columns expected for the η2 structure whose unit cell is represented by the rectangular box. Microstructures were viewed along <112>Al.

Fig. 4. HAADF-STEM images showing precipitates near the grain boundaries of samples peak-aged at (a, d) 120 °C, (b, e) 165 °C and (c, f) 180 °C. The upper images are for directly aged samples (a-c) while the lower ones for naturally pre-aged samples (d-f). The dashed arrows point to pores left by particles dropped or dissolved during TEM specimen preparation. Microstructure for one of the neighboring grains was viewed along <110>Al.

Fig. 5. HAADF-STEM characterization of the precipitation in the vicinity of grain boundaries: (a) sub-/grain structures highlighting the high density of grain boundaries; (b) the formation of precipitate-sparse zone (PSZ) containing gradient nano-precipitates near grain boundary in a region boxed in (a); (c) the change of precipitate size with the distance from the grain boundary in the PSZ.

Fig. 6. Grain size dependent precipitation in the samples directly aged at 180 °C: (a) HAADF-STEM images showing precipitates within a grain with a grain boundary spacing of ~653 nm; (b) bright-field TEM images showing precipitates within a grain with a grain boundary spacing of ~302 nm; (c) upturn fraction of the PFZ + PSZ over the entire grain with the decline of the GB spacing. This fraction is represented by the ratio for the length of PFZ + PSZ over the GB spacing.

References 31

[1]	A. Azarniya, A.K. Taheri, K.K. Taheri, J. Alloys Compd. 781(2019) 945-983.
[2]	W. Xu, Y. Luo, W. Zhang, M. Fu, J. Mater. Sci. Technol. 34(2018) 173-184. DOI URL
[3]	K. Ma, H. Wen, T. Hu, T.D. Topping, D. Isheim, D.N. Seidman, E.J. Lavernia, J.M. Schoenung, Acta Mater. 62(2014) 141-155. DOI URL
[4]	T. Hu, K. Ma, T.D. Topping, J.M. Schoenung, E.J. Lavernia, Acta Mater. 61(2013) 2163-2178. DOI URL
[5]	H. Degischer, W. Lacom, A. Zahra, C. Zahra, Z. Metallk. 71(1980) 231-238.
[6]	L.K. Berg, J. Gjønnes, V. Hansen, X.Z. Li, M. Knutson-Wedel, G. Waterloo, D. Schryvers, L.R. Wallenberg, Acta Mater. 49(2001) 3443-3451. DOI URL
[7]	T.F. Chung, Y.L. Yang, M. Shiojiri, C.N. Hsiao, W.C. Li, C.S. Tsao, Z. Shi, J. Lin, J.R. Yang, Acta Mater. 174(2019) 351-368.
[8]	A. Bendo, K. Matsuda, S. Lee, K. Nishimura, N. Nunomura, H. Toda, M. Yamaguchi, T. Tsuru, K. Hirayama, K. Shimizu, H. Gao, K. Ebihara, M. Itakura, T. Yoshida, S. Murakami, J. Mater. Sci. 53(2017) 4598-4611. DOI URL
[9]	C.D. Marioara, W. Lefebvre, S.J. Andersen, J. Friis, J. Mater. Sci. 48(2013) 3638-3651. DOI URL
[10]	F. Cao, J. Zheng, Y. Jiang, B. Chen, Y. Wang, T. Hu, Acta Mater. 164(2019) 207-219. DOI URL
[11]	M. de Hass, J.T.M. De Hosson, Scr. Mater. 44(2001) 281-286.
[12]	H. Jiang, R.G. Faulkner, Acta Mater. 44(1996) 1857-1864.
[13]	T. Marlaud, B. Malki, C. Henon, A. Deschamps, B. Baroux, Corros. Sci. 53(2011) 3139-3149. DOI URL
[14]	H. Zhao, F. De Geuser, A. Kwiatkowski da Silva, A. Szczepaniak, B. Gault, D. Ponge, D. Raabe, Acta Mater. 156(2018) 318-329. DOI URL
[15]	J.H. Zheng, J. Lin, J. Lee, R. Pan, C. Li, C.M. Davies, Int. J. Plasticity 106 (2018) 31-47. DOI URL
[16]	M. Navaser, M. Atapour, J. Mater, Sci. Technol. 33(2017) 155-165. DOI URL
[17]	Y.L. Wang, H.C. Jiang, Z.M. Li, D.S. Yan, D. Zhang, L.J. Rong, J. Mater, Sci. Technol. 34(2018) 1250-1257.
[18]	M.A. Krishnan, V.S. Raja, S. Shukla, S.M. Vaidya, Metall. Mater. Trans. A 49 (2018) 2487-2498.
[19]	J. Gubicza, I. Schiller, N.Q. Chinh, J. Illy, Z. Horita, T.G. Langdon, Mater. Sci. Eng. A 460-461(2007) 77-85. DOI URL
[20]	J.A. Österreicher, G. Kirov, S. S.A.Gerstl, E. Mukeli, F. Grabner, M. Kumar, J. Alloys Compd. 740(2018) 167-173. DOI URL
[21]	C.H. Liu, Y.X. Lai, J.H. Chen, G.H. Tao, L.M. Liu, P.P. Ma, Scr. Mater. 115(2016) 150-154. DOI URL
[22]	C.H. Liu, P.P. Ma, L.H. Zhan, M.H. Huang, J.J. Li, Scr. Mater. 155(2018) 68-72. DOI URL
[23]	P.P. Ma, L.H. Zhan, C.H. Liu, Q. Wang, H. Li, D.B. Liu, Z.G. Hu, J. Alloys Compd. 790(2019) 8-19. DOI URL
[24]	S. Pogatscher, E. Kozeschnik, H. Antrekowitsch, M. Werinos, S. S.A.Gerstl, J.F. Löffler, P.J. Uggowitzer, Scr. Mater. 89(2014) 53-56. DOI URL
[25]	M. Madanat, M. Liu, J. Banhart, Acta Mater. 159(2018) 163-172. DOI URL
[26]	K. Omer, A. Abolhasani, S. Kim, T. Nikdejad, C. Butcher, M. Wells, S. Esmaeili, M. Worswick, J. Mater, Process. Technol. 257(2018) 170-179. DOI URL
[27]	B. Cai, B. Adams, T. Nelson, Acta Mater. 55(2007) 1543-1553. DOI URL
[28]	T. Marlaud, A. Deschamps, F. Bley, W. Lefebvre, B. Baroux, Acta Mater. 58(2010) 4814-4826. DOI URL
[29]	H. Jiang, R.G. Faulkner, Acta Mater. 44(1996) 1865-1871.
[30]	J. Banhart, M.D.H. Lay, C.S.T. Chang, A.J. Hill, Phys. Rev. B 83 (2010) 287-292.
[31]	H.S. Zurob, H. Seyedrezai, Scr. Mater. 61(2009) 141-144.