Influence of Pre-deformation on Aging Precipitation Behavior of Three Al-Cu-Li Alloys

doi:10.1007/s40195-016-0519-6

Abstract

Abstract:

The influence of pre-deformation on aging precipitates of three near peak-aged Al-Cu-Li alloys, 1460 alloy with a low Cu/Li ratio (1.46), 2050 alloy with a high Cu/Li ratio (4.51) and 2A96 alloy with a medium Cu/Li ratio (2.97), was investigated. The strength of the aged alloys is enhanced by the pre-deformation. The effectiveness of pre-deformation on precipitates is dependent on the alloy’s composition. With increasing the pre-deformation, the population density of T1 (Al₂CuLi) precipitates increases in all three Al-Cu-Li alloys and their diameter decreases in 2050 and 2A96 alloys, and the greatest effectiveness is observed in 2A96 alloy. The pre-deformation also increases the population density of θ′ (Al₂Cu) precipitates and decreases their diameter in 2050 and 2A96 Al-Li alloys, but the effectiveness is smaller compared to that on T1 precipitates. In 1460 alloy subjected to two-step aging at 130 °C for 20 h followed by 160 °C for 12 h, the main precipitates are δ′ (Al₃Li). At 2%-6% pre-deformation, GP-I zones form and pre-deformation displays little influence. Eight percentage pre-deformation promotes θ″/θ′ precipitation and increases their population density.

Key words: Al-Li alloy, Pre-deformation, Aging, Precipitates

Jin-Feng Li,Zhi-Hao Ye,Dan-Yang Liu,Yong-Lai Chen,Xu-Hu Zhang,Xiu-Zhi Xu,Zi-Qiao Zheng. Influence of Pre-deformation on Aging Precipitation Behavior of Three Al-Cu-Li Alloys[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(2): 133-145.

Figures/Tables 15

Table 1 Chemical compositions of the experimental Al-Cu-Li alloys (mass fraction, %)

Alloy	Cu	Li	Mg	Ag	Zn	Mn	Zr	Ce	Al	Cu/Li ratio
1460	3.12	2.14	-	-	-	-	0.11	0.05	Bal.	1.46 (low)
2050	3.56	0.79	0.4	0.4	-	0.3	0.11	-	Bal.	4.51 (high)
2A96	3.81	1.28	0.39	0.4	0.4	0.3	0.12	-	Bal.	2.97 (medium)

Table 2 T8 aging for different Al-Cu-Li alloy

Alloy	Pre-deformation (%)	Aging temp./time
1460	2, 4, 6, 8	130 °C/20 h +160 °C/12 h
2050	2, 5, 8, 10	155 °C/32 h
2A96	0	160 °C/20 h, 78 h, 120 h
2A96	3, 6, 8, 12.5	160 °C/20 h

Table 3 Tensile properties of 2A96 alloy aged after different pre-deformation

Pre-deformation	Aging temp./time	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
0	160 °C/20 h	500	356	19.1
	160 °C/78 h	589	533	7.2
	160 °C/120 h	616	565	7.7
3%	160 °C/20 h	600	551	9.7
6%	160 °C/20 h	610	578	12.7
8%	160 °C/20 h	616	585	10.9
12.5%	160 °C/20 h	610	584	9.6

Table 4 Tensile properties of 1460 alloy aged after different pre-deformation

Pre-deformation (%)	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
2	577	463	4.8
4	580	475	6.5
6	596	510	6.9
8	610	537	6.6

Table 5 Tensile properties of 2050 alloy aged after different pre-deformation

Pre-deformation (%)	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
2	448	341	13.9
5	518	479	11.2
8	538	479	10.7
10	543	489	10.9

Fig. 1 SAED patterns and TEM DF images of near peak-aged 2A96 alloys with a, b 0% (aging for 78 h), c, d 3% (aging for 20 h), e, f 8% pre-deformations (aging for 20 h), g, h 12.5% pre-deformations (aging for 20 h). a, c, e, g showing T1 precipitates, the direction is parallel to <112>Al. b, d, f, h showing θ′ precipitates, the direction is parallel to <100>Al

Table 6 Average population density and diameter of θ′ and T1 precipitates in near peak-aged 2A96 alloy with different pre-deformation

Precipitate type	Statistical source	Pre-deformation (%)	Number density (#/μm²)	Diameter (nm)
θ′	DF images along <100>_Al direction	0	56.6	75-429
		3	92.6	52-227
		8	152.9	22-132
		12.5	288.8	17-85
T1	DF images along <112>_Al direction	0	102.4	91-356
		3	365.4	22-173
		8	518.6	17-102
		12.5	1550.1	16-71

Fig. 2 SAED patterns and TEM DF images of near peak-aged 2050 alloys with a, b 2%, c, d 5%, e, f 10% pre-deformations. a, c, e showing T1 precipitates, the direction is parallel to <112>Al. b, d, f showing θ′ precipitates, the direction is parallel to <100>Al

Table 7 Average population density and diameter of θ′ and T1 precipitates in near peak-aged 2050 alloy with different pre-deformation

Precipitate type	Statistical source	Pre-deformation (%)	Number density (#/μm²)	Diameter (nm)
θ′	DF images along <100>_Al direction	2	72.4	90-330
		5	103.5	75-260
		10	110.5	20-80
T1	DF images along <112>_Al direction	2	76.1	85-170
		5	192.1	40-135
		10	260.7	20-80

Fig. 3 SAED patterns and TEM images of T8-aged 1460 alloy with a, b, c 2%, d, e, f 4% pre-deformation. a, b, d, e TEM DF images showing δ′ and GP-I(θ′′/θ′) precipitates, the direction is parallel to <100>Al. c, f TEM BF images showing T1 precipitates, the direction is parallel to <112>Al

Fig. 4 SAED patterns and TEM DF images of T8-aged 1460 alloy with a, b, c 6%, d, e, f 8% pre-deformation. a, b, d, e showing δ′ and GP-I(θ′′/θ′) precipitates, the direction is parallel to <100>Al. c, f showing T1 precipitates, the direction is parallel to <112>Al

Fig. 5 TEM BF images showing GP-I zones and θ″/θ′ precipitates in the T8-aged 1460 alloy with a 2%, b 4%, c 6%, d 8% pre-deformation. The direction is parallel to <100>Al

Table 8 Average population density and diameter of GP-I + θ″/θ′ and T1 precipitates in T8-aged 1460 alloy with different pre-deformation

Precipitate	Statistical source	Pre-deformation (%)	Number density (#/μm²)	Diameter (nm)
GP-I + θ″/θ′	BF images along <100>_Al direction	2	1304	19-68
		4	1346	20-78
		6	1476	19-124
		8	1802 (θ″/θ′)	19-108
T1	DF images along <112>_Al direction	2	27	25-122
		4	48	25-118
		6	68	23-120
		8	164	15-112

Fig. 6 Population density of T1 and θ′ precipitates in 2A96 and 2050 alloys as a function of pre-deformation

Fig. 7 [100]Al SAED pattern and DF TEM images (showing δ′ precipitates) of 1460 alloy after a aging at 130 °C for 4 h following 4% pre-deformation and b aging at 160 °C for 0.5 h. The images are taken along the [100]Al zone axis

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