EIS test results of AA2024 and AA6061 alloy in rainwater are shown in Figure (1) and figure (2) and table (3) show the resistors and capacitors that had been gained from the Nyquist plots by using equivalent circuit with fit model Constant Phase Element (CPE) as shown in figure (3) for both AA2024 and AA6061.From figure (1) and figure (2) by comparing the resistance for AA2024 and AA6061 it is clear that, In AA6061 the resistance is higher than AA2024 in rainwater.
3.2 Effect of solution treatment on electrochemical impedance spectroscopy of 2024 and 6061aircraft aluminum alloys
The Nyquist curve for EIS test results of AA2024 and AA6061 alloy in rainwater after heat treatment are shown in Figs. 4, 5, 6, and 7. Table (4) and table (5) show the resistors and capacitors that had been gained from the Nyquist plots by using CPE fit for both AA2024 and AA6061.
In Fig. (4) shows EIS test results of AA2024 alloy after heat treatment in rainwater for AA2024 of temperature (150,200,250, and 300oC) for aging 1hr, from these figure by comparing between the resistance and capacitors at the temperatures 150,200 and 250oC the resistance increase while at temperatures 300oC the resistance decrease.
Figure (5) shows EIS test results of AA2024 alloy after heat treatment in rainwater for AA2024 of temperature (150,200,250, and 300oC) for aging 2hr, from these figure by comparing between the resistance and capacitors at the temperatures 150, 200, and 250oC the resistance increase while at temperature 300oC the resistance decrease.
Figure (6) shows EIS test results of AA6061 alloy after heat treatment in rainwater for AA6061 of temperature (150,200,250, and 300oC) for aging 1hr, from these figure by comparing between the resistance and capacitors at the temperatures 150,200 and 250oC the resistance increase while at temperatures 300oC the resistance decrease.
In Fig. (7) shows EIS test results of AA6061 alloy after heat treatment in rainwater for AA6061 of temperature (150,200,250,and300oC) for aging 2hr, from these figure by comparing between the resistance and capacitors at the temperatures 200oC the resistance increase while at temperatures 150,250 and 300oC the resistance decrease.
Figure (8) and table (6) show phases obtain from XRD test. From these figure and table the maximum value for 2024AA of intensity was 100 at a position of 2θ = 44.68 for alloy 2024 aging treatment at temp.250 oC for 2hrs. For AA6061 the maximum value of intensity was 100 at a position 2θ = 44.68 for alloy 6061 aging treatment at temp. 300 oC for 1hr. After heat treatments, Al2Cu and Al2CuMg phase formed in 2024 AA while after heat treatments, Mg2Si phase formed in 6061 AA.
Figure (9) show SEM and EDS test results of AA2024 and AA6061 before and after solution heat treatment. From these tests, it is found that the change in the values of the resistors and capacitors in the EIS test are effected with the precipitated phases due to the solution treatment, as well as the formation of oxide and chloride layers as corrosion products due to rainwater environment.
Table (4) the resistors and capacitors of AA2024 alloy after solution heat treatments in rain water
alloys
|
Rp( ohms)
|
Ru( ohms)
|
Cf(µF)
|
2024,150 oC,1h
|
2.919\(\times\)103
|
45.66
|
75. 23
|
2024,150 oC,2h
|
1.993\(\times\)103
|
37.72
|
135.0
|
2024,200 oC,1h
|
2.263\(\times\)103
|
41.76
|
80.53
|
2024,200 oC,2h
|
\(3.408\times\)103
|
34.22
|
\(40.38\)
|
2024,250 oC,1h
|
4.033\(\times\)103
|
37.79
|
58.65
|
2024,250 oC,2h
|
2.802\(\times\)103
|
51.92
|
176.8
|
2024,300 oC,1h
|
2.296\(\times\)103
|
18.40
|
86.81
|
2024,300 oC,2h
|
1.556\(\times\)103
|
26.93
|
288.0
|
Table (5) the resistors and capacitors of AA6061 alloy after solution heat treatments in rainwater
alloys
|
Rp( ohms)
|
Ru( ohms)
|
Cf(µF)
|
6061,150, oC 1h
|
2.932\(\times\)103
|
47.95
|
73.64
|
6061,150 oC,2h
|
873.0
|
34.84
|
182.5
|
6061,200 oC,1h
|
847.3
|
40.94
|
175.2
|
6061,200 oC,2h
|
6.937\(\times\)103
|
39.93
|
80.19
|
6061,250 oC,1h
|
3.292\(\times\)103
|
48.01
|
67.25
|
6061,250 oC,2h
|
4.090\(\times\)103
|
20.78
|
66.57
|
6061,300 oC,1h
|
2.582\(\times\)103
|
21.60
|
152.1
|
6061,300 oC,2h
|
3.346\(\times\)103
|
26.91
|
69.49
|
Table (6) Phases obtain from XRD test
Alloys
|
phase
|
2Theta
|
I/I1
|
Crystal system
|
AA2024 solution heat treatment and aging at temp.250 oC for 2hrs.
|
Al
|
38.43, 44.68, 65.04, 78.19, 78.44
|
81,100,97,29,97.65
|
Cubic
|
AA2024 solution heat treatment and aging at temp.250 oC for 2hrs.
|
Al2CuMg
|
27.24,39.24,
42.88,44.68, 64.28,65.04, 66.04, 78.19, 78.44
|
6.61, 9.49, 4.10,100,
26.51,6.96,
97, 29 ,6.96
|
Orthorhombic
|
AA2024 solution heat treatment and aging at temp.250 oC for 2hrs
|
Al2 Cu
|
42.88, 65.04, 66.04, 78.44
|
4.10,97,6.96,6.96
|
Tetragonal
|
AA6061 solution heat treatment and aging at temp.300 oC for 1hr.
|
Al
|
38.44, 44.68, 65.04, 78.16,
|
44,100,53,30
|
Cubic
|
AA6061 solution heat treatment and aging at temp.300 oC for 1hr.
|
Mg2Si
|
40.12, 78.16
|
5.22,30
|
Cubic
|