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Journal of Chinese Society for Corrosion and protection  2018, Vol. 38 Issue (2): 183-190    DOI: 10.11902/1005.4537.2017.054
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Intergranular Corrosion Behavior of T6 Aging Treated Micro-alloyed Al-Cu-Li Alloys with Mg/Ag/Zn
Danyang LIU1,2, Jiexia WANG1, Jinfeng LI1,2(), Yonglai CHEN3, Xuhu ZHANG3, Xiuzhi XU3, Ziqiao ZHENG1
1 School of Materials Science and Engineering, Central South University, Changsha 410083, China
2 Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center, Central South University, Changsha 410083, China
3 Aerospace Research Institute of Materials and Processing Technology, Beijing 100076, China
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Abstract  

Ingots of four Al-Cu-Li alloys with different amounts of micro-alloying elements of Mg, Zn and Ag respectively were prepared via melt and casting technique, which were successively hot- and cold-rolled to produce sheets of 2 mm in thickness and finally subjected to T6 aging treatment. Further,the intergranular corrosion behavior of the above T6 aged alloys was studied in solution of 57 g /L NaCl+10 mL/L H2O2. The result showed that the Al-Cu-Li alloys with micro-alloying element of Mg, Zn, and Mg+Zn respectively present more or less the same evolution tendency of intergranular corrosion behavior, namely, local IGC emerges at the initial aging stage, general IGC at the under peak aging stage, local IGC at the peak aging stage and pitting with slight IGC at the over-peak aging stage with the prolonging T6 heat treatment. But the IGC susceptibility of the Zn- alloyed Al-Cu-Li alloy is weaker than that of the Mg-alloyed one. Intergranular corrosion morphology of Mg+Ag-alloyed Al-Cu-Li alloy was different from that of the above three alloys, showing pitting with IGC at peak aging stage, local IGC or general IGC at other aging stages. The mechanism of intergranular corrosion of Mg+Ag-alloyed Al-Cu-Li Alloy is anodic dissolution derived by the potential-difference between the precipitates free zone (PFZ) and numerous amount of continuous precipitates of T1 phase at grain boundaries.

Key words:  Al-Cu-Li alloy      intergranular corrosion      micro-alloying     
Received:  13 April 2017     
Fund: Supported by National Foundation of China (TDZX-17-005-1)

Cite this article: 

Danyang LIU, Jiexia WANG, Jinfeng LI, Yonglai CHEN, Xuhu ZHANG, Xiuzhi XU, Ziqiao ZHENG. Intergranular Corrosion Behavior of T6 Aging Treated Micro-alloyed Al-Cu-Li Alloys with Mg/Ag/Zn. Journal of Chinese Society for Corrosion and protection, 2018, 38(2): 183-190.

URL: 

https://www.jcscp.org/EN/10.11902/1005.4537.2017.054     OR     https://www.jcscp.org/EN/Y2018/V38/I2/183

Alloy Cu Li Mg Ag Zn Mn Zr Al
2#(Zn) 3.34 1.20 --- --- 0.4 0.3 0.1 Bal.
3#(Mg) 3.26 1.07 0.4 --- --- 0.3 0.1 Bal.
4#(Mg+Zn) 3.34 1.16 0.4 --- 0.4 0.3 0.1 Bal.
5#(Mg+Ag) 3.28 1.07 0.4 0.4 --- 0.3 0.1 Bal.
Table 1  Chemical compositions of four Al-Cu-Li alloys
(mass fraction / %)
Fig.1  Cross-sectional morphologies of Al-Li alloys adding with Mg+Zn aging for 0.5 h (a), Mg+Ag aging for 80 h (b), Mg+Ag aging for 36 h (c) and Zn aging for 28 h (d)
Fig.2  Micro-hardness (a) and typical corrosion morphologies of Zn-containing alloy 2# aged at 175 ℃ for 0.5 h (b), 4 h (c), 28 h (d), 36 (e) and 120 h (f)
Fig.3  Micro-hardness (a) and representative corrosion morphologies of Mg-containing alloy 3# aged at 175 ℃ for 0.5 h (b), 4 h (c), 28 h (d) and 120 h (e)
Fig.4  Micro-hardness (a) and representative corrosion morphologies of Mg+Zn containing alloy 4# aged at 175 ℃ for 0.5 h (b), 4 h (c), 28 h (d) and 120 h (e)
Fig.5  Micro-hardness (a) and representative corrosion morphologies of Mg+Ag containing alloy 5# aged at 175 ℃ for 0.5 h (b), 4 h (c), 28 h (d), 36 (e) and 120 h (f)
Aging-T6-175 ℃ Dominant corrosion mode IGC depthμm Max IGC depthμm Pitting corrosion depthμm Max pitting depthμm
Alloy Time / h
Mg
(3#)
0.5 Local IGC with pitting 167.98 270.70 127.60 178.13
3 Local IGC with pitting 99.22 100.50 109.10 138.28
4 Local IGC with pitting 270.12 321.68 158.04 208.60
28 Pitting --- --- 162.01 239.65
36 Pitting --- --- 144.00 220.02
40 Pitting --- --- 125.73 162.01
64 Pitting --- --- 113.78 161.14
80 Pitting --- --- 145.15 218.85
120 Pitting --- --- 169.21 254.88
Zn
(2#)
0.5 Local IGC with pitting 176.23 253.72 78.32 128.91
4 Local IGC with pitting 170.88 232.91 70.25 113.67
28 Pitting --- --- 116.87 148.83
36 Pitting --- --- 107.69 151.76
40 Pitting --- --- 144.50 198.93
45 Pitting --- --- 163.71 196.00
57 Pitting --- --- 144.30 217.68
64 Pitting --- --- 146.07 212.11
72 Pitting --- --- 83.13 108.98
120 Pitting --- --- 143.35 204.49
Table 2  Dominant corrosion mode, IGC depth,max IGC depth, pitting corrosion depth, max pitting depth of the alloys 2# and 3#
Aging-T6-175 ℃ Dominant corrosion mode IGC depthμm Max IGC depthμm Pitting corrosion depthμm Max pitting depthμm
Alloy Time / h
Mg+Zn (4#) 0.5 Local IGC with pitting 136.11 187.50 121.99 195.12
4 Local IGC with pitting 112.18 249.32 36.63 41.90
28 Pitting --- --- 120.82 165.53
36 Pitting --- --- 142.84 176.37
40 Pitting --- --- 112.86 173.44
64 Pitting --- --- 160.76 212.16
80 Pitting --- --- 139.75 291.5
120 Pitting --- --- 140.63 222.66
Mg+Ag (5#) 0.5 Local IGC with pitting 155.74 191.60 106.40 174.03
4 Local IGC with pitting 175.43 215.04 106.00 123.05
28 Local IGC with pitting 149.10 252.25 119.27 228.22
36 Local IGC with pitting 125.10 148.84 111.96 139.45
40 Local IGC with pitting 147.31 195.12 108.32 147.66
64 Local IGC with pitting 122.83 143.26 111.69 162.01
80 Local IGC with pitting 184.04 248.15 104.01 145.02
120 Local IGC with pitting 137.34 181.06 109.51 131.55
Table 3  Dominant corrosion mode, IGC depth,max IGC depth, pitting corrosion depth, max pitting depth of the alloys 4# and 5#
Fig.6  TEM images of the alloys 3#,4# and 5# under peak-aged condition: (a) 3#, DF, <112>α; (b) 3#, DF, <112>α; (c)4#, DF, <100>α; (d) 4#, DF, <112>α; (e) 5#, DF, <100>α; (f) 5#, DF, <112>α (DF: dark field)
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