Improved Properties in Relation to Fine Precipitate Microstructures Tailored by Combinatorial Processes in an Al-Cu-Mg-Si Alloy

doi:10.1007/s40195-020-01093-1

摘要/Abstract

Abstract:

The 2xxx series Al alloys have been widely used in aerospace industry owing to their high strength, good plasticity and superior formability. To ensure a good control of shape, the quenched alloy sheets require a small pre-deformation before artificial aging. However, this pre-deformation considerably deteriorates the mechanical strength of the Al-3.0Cu-1.8Mg-0.5Si (wt%) alloys due to the formation of unfavorable large-sized precipitates at dislocations. To tackle this issue, we designed a pre-aging process prior to the pre-deformation. The thermal-mechanical treatment, involving pre-aging, pre-deformation and subsequent aging, markedly enhanced the ultimate tensile strength up to 521 MPa compared to that (448 MPa) of the alloy without pre-aging. Microstructure characterization revealed that the fine precipitates (~ 2 nm) with a uniform dispersion were promoted within the Al matrix, which in turn partly suppressed the formation of the unfavorable large-sized precipitate (~ 100 nm). Our findings provide a new clue for designing stronger Al alloys with age-hardenability.

Key words: Aluminum alloys, Thermo-mechanical treatment, Precipitation, Age-hardenability

. [J]. 金属学报英文版, 2020, 33(11): 1527-1534.

Fengjiao Niu, Jianghua Chen, Cuilan Wu, Jing Wu, Xiandong Xu, Pan Xie, Xiongwei Yu. Improved Properties in Relation to Fine Precipitate Microstructures Tailored by Combinatorial Processes in an Al-Cu-Mg-Si Alloy[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(11): 1527-1534.

图/表 8

Table 1 Detailed process of the heat treatments used in this article

Heat treatment	Detailed process
T6	ST + WQ + AA at 180 °C
T8	ST + WQ + 6% CR + AA at 180 °C
NA7d-TMT	ST + WQ + NA for 7 days + 6% CR + AA at 180 °C
AA1h-TMT	ST + WQ + AA at 200 °C for 1 h + 6% CR + AA at 180 °C

Fig. 1 a Hardness-time curves of the Al-3.0Cu-1.8Mg-0.5Si alloy pre-aged at RT and 200 °C, and samples marked with arrows are selected to undergo the TMT processes, b Vickers hardness plotted against aging time curves of the samples treated by T6, T8 temper and TMT processes aging at 180 °C

Fig. 2 HAADF-STEM images of the peak-aged samples treated by T6 temper a, b, T8 temper c, d

Table 2 Mechanical properties of the peak-aged samples with different heat treatments

Heat treatment	Peak-aging time (h)	Peak hardness (HV)	σ_0.2 (MPa)	σ_b (MPa)	ε (%)
T6	48	153	411	469	9.9
T8	18	140	429	448	7.8
AA1h-TMT	9	157	454	500	7.3
NA7d-TMT	24	163	485	521	8.3

Fig. 3 Bright-field TEM image a and HAADF-STEM image b of the samples pre-aged at 200 °C for 1 h. The inset in b showing the structure of a precursor

Fig. 4 HAADF-STEM images of the peak-aged samples treated by AA1h-TMT process a-c and NA7d-TMT process d-f viewed along the [001]Al direction

Fig. 5 Low-magnification HAADF-STEM images of the peak-aged samples treated by T8 temper a, b, AA1h-TMT process, c, d, NA7d-TMT process, e, f viewed along the [001]Al direction

Table 3 Precipitates of the peak-aged samples with different heat treatments

Heat treatment	Main precipitates
Heat treatment	Dislocation-induced precipitates	Dislocation-free precipitates
T6	-	Si-modified GPB zones
T8	The coarse CPs (~ 100 nm)	Si-modified GPB zones
AA1h-TMT	A small amount of CPs (~ 50 nm)	A large amount of Si-modified GPB zones
NA7d-TMT	A small amount of CPs (~ 50 nm), some rod-like S phase	A large amount of Si-modified GPB zones

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