Effects of Thermal Damage on the Strength
Properties of 7050-T7451 and 7075-T7351 Aluminium
Alloys
Jaime Calero and Suzana Turk
Air Vehicles Division
Defence Science and Technology Organisation
DSTO-TR-2104
ABSTRACT
This report presents experimental test data that quantify the effects of thermal damage on
the strength properties of 7050-T7451 and 7075-T7351 aluminium alloys. The test results
indicate that there is a direct relationship between hardness and strength properties that
can be used to determine residual strength of these alloys at room temperature after
thermal damage. This relationship can be expressed as a function of hardness number by
the use of exponential equations.
RELEASE LIMITATION
Approved for public release
Published by
Air Vehicles Division
DSTO Defence Science and Technology Organisation
Fishermans Bend, Victoria 3207 Australia
Telephone: (03) 9626 7000
Fax: (03) 9626 7999
© Commonwealth of Australia 2008
AR-014-106
February 2008
APPROVED FOR PUBLIC RELEASE
Effects of Thermal Damage on the Strength
Properties of 7050-T7451 and 7075-T7351 Aluminium
Alloys
Executive Summary
An extensive test program was conducted to quantify the effects of thermal damage on the
strength properties of 7050-T7451 and 7075-T7351 aluminium alloys. The program was
initiated in response to the need to provide comprehensive experimental data on thermal
damage. These data could be used to quantify room temperature residual strength
properties of airframe structures and components that have been exposed to temperatures
above 205°C.
The data show that both alloys have a similar response to thermal damage and that there
is a direct relationship between hardness and strength properties. This relationship can be
expressed by the use of exponential equations of the hardness number and strength data.
As a result it was possible to use hardness and electrical conductivity testing to estimate
the residual strength at room temperature after thermal damage had occurred. The test
results also revealed that exposure at 315°C for more than 60 minutes eventually results in
partial recovery of strength following the initial decrease in strength properties. A similar
phenomenon was observed in the specimens tested at 350°C. It is expected however that
this trend will revert as other factors that affect the strength of the alloy evolve. This
behaviour should not be interpreted as an indication of recovery of properties but instead
as a sign of possible severe thermal damage.
It is envisaged that calculations based on these data could be used in structural integrity
models to estimate room temperature residual strength properties of damaged structures
and components made from these alloys.
Contents
1. INTRODUCTION............................................................................................................... 1
2. OBJECTIVES........................................................................................................................ 2
3. TEST DETAILS.................................................................................................................... 2
4. TEST RESULTS ................................................................................................................... 5
4.1 7050-T7451 Aluminium alloy - Test Results ........................................................ 5
4.1.1
Sub-size Tension (SST) Specimens .......................................................... 5
4.1.2
Round Tension (RT) Specimens .............................................................. 9
4.2 7075-T7351 Aluminium alloy - Test results.......................................................... 9
4.2.1
Sub-size Tension (SST) Test Specimens.................................................. 9
4.2.2
Round Tension (RT) Test Specimens .................................................... 13
5. DISCUSSION .................................................................................................................... 13
6. FURTHER COMMENTS ................................................................................................. 19
7. CONCLUSIONS................................................................................................................ 19
8. ACKNOWLEDGEMENT................................................................................................. 20
9. REFERENCES .................................................................................................................... 20
APPENDIX A:
TABLES ...................................................................................................... 21
DSTO-TR-2104
1. Introduction
Two of the most extensively used materials in aircraft structures are 7050-T7451 and
7075-T7351 aluminium alloys. However, exposure to temperatures above the specified ageing
temperature of these alloys (Table 1) has deleterious effects on their mechanical properties.
The extent of any damage caused by excessive heating after heat treatment is primarily
dictated by the exposure time and temperature that the affected component/area experiences.
When thermal damage is suspected, assessment of affected areas might be required to assess
the structural integrity or to design a repair process for the affected area. For this purpose,
hardness and electrical conductivity tests have generally been used to estimate residual
strength properties of aircraft structures and components affected by thermal damage [1, 2, 3].
Thermal damage assessment is achieved by measuring the relative changes in hardness and
electrical conductivity of affected areas and comparing them with reference values measured
at unaffected areas; these results are subsequently correlated to strength properties. However,
data on thermal damage are limited to specific conditions.
Consequently, a test program that covers a wide range of exposure conditions was set up to
quantify the effects of thermal damage on the strength properties of these alloys. The test
program used hardness and electrical conductivity testing as a means of quantifying the
residual strength properties of these alloys at room temperature after thermal damage had
occurred.
This report is part of a series of tests conducted to quantify the effects of thermal damage on
hardness and electrical conductivity, fatigue life, fracture toughness and the microstructure of
these alloys.
Table 1.
Recommended age-hardening heat treatment for 7050-T7451 and 7075-T7351 aluminium
plates (from W51 1 condition before ageing) [4]
Alloy
Solution Heat
Treating
Temperature
(°C)
7050
7075
1st Step
2nd Step
Temperature (°C)
Time (Hrs)
Temperature (°C)
Time
(Hrs)
471 to 482
116 to 127
3 to 6
157 to 168
24 to 30
460 to 499 *
102 to 113
6 to 8
157 to 168
24 to 30
* For plates over 101.6 mm thick, a maximum temperature of 488°C is recommended to avoid eutectic melting.
W51: Solution heat-treated, this is an unstable temper and applies specifically to plate, to rolled or
cold-finished rod and bar, to die or ring forgings, and to rolled rings.
1
1
DSTO-TR-2104
2. Objectives
The objectives of the tests presented in this report are (i) to quantify variations in strength
properties (at room temperature) resulting after thermal damage at temperatures above 205ºC;
and (ii) to explore the ability of hardness and eddy current electrical conductivity tests to
estimate room temperature residual strength after thermal damage. It is envisaged that
calculations based on these data might be used in structural integrity calculations to manage
affected areas of service components. These data can also be linked to fatigue life [5, 6 ] in the
same way that hardness is linked to strength properties.
3. Test Details
Testing for determination of yield (Fty) and ultimate tensile (Ftu) strengths were performed
on round tension (RT) (12.5 mm diameter) and sub-size tension (SST) (6 mm square section)
test specimens (Figure 1) to ASTM B 557M – 94, Standard Test Methods of Tension Testing
Wrought and Cast Aluminium – and Magnesium – Alloy Products [7]. Testing was conducted
using an Instron 50 KN tensile test machine. Machining of the specimens to final dimensions
was performed after thermal damage. All testing was conducted at room temperature in a
laboratory controlled environment.
The round tension specimens were introduced to explore the possibility of variations in the
test results caused by a larger-cross section compared to that of the sub-size tension
specimens.
Figure 1. Schematic of (Top) round tension and (bottom) sub-size tension test specimens. Drawings
not to scale, all dimensions in millimetres
2
DSTO-TR-2104
The specimens, cut in the longitudinal direction, were manufactured from rolled aluminium
alloy plate 7050-T7451 (127 mm thick) to AMS 4050 and from 7075-T7351 (50.8 mm thick) to
QQ-A-250/12. Table 2 presents the mechanical properties and Table 3 the chemical
composition of the plates as specified in the respective certificates of conformity.
Table 2.
Mechanical properties of aluminium alloy plates used to manufacture the tension test
specimens. Results are as specified in the respective certificate of conformity
Property
7050-T7451
7075-T7351
Ftu, MPa
530.8 – 533*
489.5 – 496*
Yield, MPa
474 – 478*
418.5 – 424*
Hardness, HRB
N/A
N/A
% Elongation
10.00*
Electrical conductivity,
41.3 – 41.64
%IACS
* Properties in the longitudinal direction.
6*
40.7 – 40.9
Table 3. Aluminium alloy composition in weight percentage
Element
Silicon
Chromium
Copper
Iron
Magnesium
Manganese
Bismuth
Titanium
Zinc
Zirconium
Others, each
Others, Total
Aluminium
7050
7075
Certificate of conformity
AMS 4050H
Certificate of conformity
QQ-A-250/12F
<0.1
2.2
0.08
2.0
0.01
0.03
0.03
6.4
0.11
0.05
0.15
Remainder
0.12 max
0.04 max
2.0-2.6
0.15 max
1.9-2.6
0.10 max
--0.06 max
5.7-6.7
0.08-0.15
0.05 max
0.15
Remainder
0.08
--1.6
0.31
2.5
0.03
--0.02
5.6
------Remainder
0.40 max
0.18-0.28
1.2-2.0
0.50 max
2.1-2.9
0.30 max
--0.20 max
5.1-6.1
--0.05 max
0.15 max
Remainder
Because hardness and electrical conductivity properties are the basis of thermal damage
assessment, it was necessary to assess whether significant variations in these properties
existed within each plate. To test this, Rockwell hardness test2 B scale (HRB) and eddy current
electrical conductivity 3 tests through the thickness of the aluminium alloy plates cross section
were performed. The test results revealed that minimum hardness and maximum electrical
conductivity values were measured at the core of the plates (Table 4). In contrast, the opposite
was true for the surface of the plates. Variations of these properties, from surface to the core of
Performed using a Wilson Rockwell Hardness Tester Series 500 machine.
Performed using a SIGMATEST D 2.068 eddy current electrical conductivity test unit (Software
Version 3.0).
2
3
3
DSTO-TR-2104
the plates, were attributed to mechanical work and to the solidification process and heat
treatment, which produced a significantly larger grain size and less optimum distribution of
secondary phases in the core material.
Table 4.
DSTO test results. Minimum hardness and maximum electrical conductivity values were
measured at the core of the plates.
Test
Hardness, HRB
Electrical conductivity, %IACS
7050-T7451
82.7 - 89.43
39.9 – 40.8
7075-T7351
84.1 – 88.67
40.0 – 40.95
The test matrix showing the number of 7050-T7451 and 7075-T7351 aluminium alloy
specimens tested is presented in Table 5. A fluidised bed furnace was used to induce thermal
damage in the specimens. In addition, to allow for through thickness homogeneous
temperature, the exposure time started four minutes after the specimens were loaded into the
furnace. Steady air-cooling was used to cool down the specimens to room temperature.
Table 5.
Test matrix showing the number of specimens and the exposure conditions
Exp Temp,
°C
205 (450°F)
232 (450°F)
260 (500°F)
315 (599°F)
350 (662°F)
Total
4
7050
7075
Exp Time
(minutes)
Round Tension
Sub-size Tension
Round Tension
Sub-size Tension
---
3
2
3
3
10
30
60
300
10
30
60
300
10
30
60
300
10
30
60
300
10
30
60
300
3
3
3
3
2
3
3
3
26
--3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
59
3
3
3
3
3
3
2
3
3
29
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
51
DSTO-TR-2104
4. Test Results
4.1 7050-T7451 Aluminium alloy - Test Results
4.1.1 Sub-size Tension (SST) Specimens
The test results (Table 6 Appendix A) showed that as the exposure temperature increases
above 205°C, the yield and ultimate tensile strengths rapidly decrease. The higher the
exposure temperature and exposure time the greater the reduction in strength properties.
However, following the initial decrease, an increase in strength was measured after
60 minutes exposure at 315°C. Beyond this exposure condition, the strength properties begin
to increase slightly; suggesting that the alloy is partially recovering its strength. For example,
the room temperature ultimate tensile strength measured after 300 minutes exposure at 350°C
(denoted as ’A’ in Figure 2) was slightly higher than that measured in specimens exposed at
232°C for 300 minutes (denoted as ‘B’ in Figure 2). In comparison, the yield strength was
lower than that measured after 232°C for 300 minutes (denoted as ‘A’ in Figure 3), but still
higher than that measured after exposure at 260°C (denoted as ‘B’ in Figure 3). It is interesting
to note that different exposure conditions resulted in an equivalent degree of deterioration.
The exposure condition where a partial recovery in properties is observed has also been called
the ‘inversion point’ [1].
7050-T7451 Aluminium Alloy SST Specimens
Ultimate Tensile Strength (Ftu), MPa
500
o
400
(A) 350 C, 369.63 MPa
o
(B) 232 C, 352.94 MPa
300
o
205 C
PC
200
o
o
232 C
o
315 C
260
o
350 C
100
0
50
100
150
200
Exposure time, minutes
250
300
Figure 2. Ultimate tensile strength at room temperature after thermal damage as noted. Exponential
curve fits are applied to these data.
5
DSTO-TR-2104
7050-T7451 Aluminium Alloy SST Specimens
500
o
PC
205 C
o
o
232 C
260 C
Yield Strength (Fty), MPa
o
o
315 C
350 C
400
300
o
(A) 232 C, 243.93 MPa
o
350 C, 199.63 MPa
200
o
(B) 260 C, 185.79 MPa
100
0
50
100
150
200
250
300
Exposure time, minutes
Figure 3. Yield strength at room temperature after thermal damage as noted. Exponential curve fits
are applied to these data.
The recovery in strength beyond the inversion point is also manifested, as expected, in an
increase in hardness. For example in Figure 4, the data show that hardness at the room
temperature after 300 minutes exposure at 350°C (denoted as ‘A’) is higher than that
measured after 60 minutes at 315°C (denoted as ‘B’).
100
7050-T7451 Aluminum Alloy SST Specimens
90
PC
o
232 C
o
315 C
Hardness, HRB
80
o
205 C
o
260 C
o
350 C
70
0
(A) 350 C (58.65 HRB)
60
50
40
0
(B) 315 C (28.2 HRB)
30
20
0
50
100
150
200
250
300
Exposure time, minutes
Figure 4. Hardness number at room temperature after thermal damage at indicated conditions.
Exponential curve fits are applied to these data.
6
DSTO-TR-2104
The inversion point of this alloy is better visualised when electrical conductivity is plotted
against hardness number (Figure 5). The partial recovery of properties creates a loop in the
value measured and as a consequence, beyond the inversion point the same electrical
conductivity could correspond to two different hardness numbers (e.g. points ‘A’ and ‘B’ in
Figure 5). Similarly, a comparable hardness number could correspond to two different
electrical conductivity vales (e.g. points ‘A’ and ‘C’ in Figure 5).
100
7050-T7451 Aluminum Alloy SST Specimens
PC
(B) (41.5 %IACS,
84.43 HRB)
Hardness Number, HRB
80
(A) (41.5 %IACS,
58.65 HRB)
(C) (45.5 %IACS,
58.6 HRB)
60
40
20
o
205 C
o
260 C
o
232 C
o
315 C
o
350 C
0
39
40
41
42
43
44
Electrical Conductivity, %IACS
45
46
47
Figure 5. Electrical conductivity and hardness number at room temperature after thermal damage at
the indicated conditions. The arrow indicates increasing temperature and exposure time. C
is an estimated datum.
The loop in properties (and the ambiguous results) is also observed when strength properties
are plotted against electrical conductivity (Figure 6) and hardness number (Figure 7). In this
case, the same electrical conductivity could correspond to two significantly different strength
levels. For example in Figure 6, an electrical conductivity of 41.50 %IACS (denote as ‘A’) could
correspond to an ultimate tensile strength of 371 MPa or 501 MPa (denoted as ‘B’).
In the case of hardness number versus strength properties, the data shows that hardness and
strength properties rapidly decrease with increasing exposure temperature (Figure 7). It also
shows a small recovery in properties once the inversion point has been passed. For example,
the strength measured at room temperature after exposure at 315°C for 10 minutes (denoted
as ‘A‘ in Figure 7) was lower than that measured after exposure at 350°C for 30 minutes
(denoted as ‘B‘ in Figure 7).
However, ambiguous results beyond the inversion point were not as significant as in the case
of the electrical conductivity. Equivalent thermal exposure condition, beyond the inversion
point, that resulted in comparable hardness number showed similar strength levels. The good
correlation between hardness and strength levels, even beyond the inversion point allows
fitting of exponential curves to test data.
7
DSTO-TR-2104
600
7050-T7451 Aluminum Alloy SST Specimens
PC
80
(B) 501.6 MPa
60
400
300
(A) 371.3 MPa
40
200
o
o
205 C
232 C
o
41.5 %IACS
Ultimate Tensile Strength, ksi
Ultimate Tensile Strength, MPa
500
o
260 C
315 C
o
350 C
20
100
40
41
42
43
44
45
46
Electrical Conductivity, %IACS
Figure 6. Strength properties at room temperature after thermal damage at the indicated conditions.
The arrow indicates increasing temperature and exposure time.
200
160 140
Hardness Number, HV
120
100
90
80
70
600
PC
7050-T7451 Aluminum Alloy SST Specimens
80
Colour Code:
500
o
o
205 C
232 C
o
o
260 C
315 C
o
60
400
Strength, ksi
Strength, MPa
350 C
Ftu
Fty
300
40
(A) 10 minutes, 21.65 HRB, 145.47 Mpa
200
20
(B) 300 minutes, 58.65 HRB, 199.63 Mpa
100
100
80
60
40
20
0
Hardness Number, HRB
Figure 7. Strength properties at room temperature after thermal damage at indicated conditions. The
direction of the arrows indicates increasing temperature and time.
8
DSTO-TR-2104
4.1.2 Round Tension (RT) Specimens
The test results for the round tension specimens are presented in Figure 8 and Table 7
Appendix A. The results for these specimens were similar to those of the sub-size tension
specimens. The main difference was that the strength of the round tension specimens (in the
pristine condition and after thermal damage) showed lower hardness and strength than those
measured for the sub-size tension specimens in similar condition. An explanation for these
differences is that the round tension specimens were cut from areas near to or at the core of
the plate (The core of the plate shows the lowest strength and hardness [8]). A limited number
of round tension specimens were tested; hence it was not possible to reach the conditions
where the inversion point is observed.
200
160 140
Hardness Number, HV
120
100
90
80
70
600
7050-T7451 Aluminum Alloy RT Specimens
PC
80
Colour Code:
500
o
205 C
o
260 C
o
232 C
o
315 C
350 C
60
400
Ftu
Fty
300
Strength, ksi
o
40
200
20
100
100
80
60
40
20
0
Hardness Number, HRB
Figure 8. Strength properties at room temperature after thermal damage at indicated conditions.
Exponential curves fit have been applied to these data. PC= Pristine condition.
4.2 7075-T7351 Aluminium alloy - Test results
4.2.1 Sub-size Tension (SST) Test Specimens
The test results for the sub-size tension test specimens are presented in Table 8 Appendix A.
The results showed that changes in ultimate tensile (Figure 9) and yield (Figure 10) strengths
and hardness (Figure 11) caused by thermal damage are quantitatively and qualitatively
similar to those of the 7050-T7451 aluminium alloy. Consequently, the residual strength
properties of the alloy at room temperature after thermal damage can also be expressed as a
function of hardness number by exponential equations.
9
DSTO-TR-2104
600
7075-T7351 Aluminium Alloy SST Specimens
Ultimate tensile Strength, MPa
500
400
300
200
o
o
205 C
o
260 C
o
350 C
100
232 C
o
315 C
PC
0
0
50
100
150
200
Exposure time, minutes
250
300
Figure 9. Ultimate tensile strength at room temperature after thermal damage at indicated conditions
600
7075-T7351 Aluminium Alloy SST Specimens
Yield Strength, MPa
500
o
o
205 C
o
260 C
o
350 C
400
232 C
o
315 C
PC
300
200
100
0
0
50
100
150
200
Exposure time, minutes
250
300
Figure 10. Yield strength at room temperature after thermal damage at indicated conditions
10
DSTO-TR-2104
100
7075-T7351 Aluminium Alloy SST Specimens
90
o
205 C
o
260 C
o
350 C
Hardness Number, HRB
80
o
232 C
o
315 C
PC
70
60
50
40
30
20
0
50
100
150
200
Exposure time, minutes
250
300
Figure 11. Hardness test results at room temperature after thermal damage at indicated conditions
Figure 12 shows the inversion point (circled area) and the ambiguity in the results measured
for electrical conductivity and ultimate tensile strength beyond the inversion point (similar
trend is observed in the yield strength, see Table 8 for results). Figure 13 presents the hardness
number versus strength properties with exponential curves fitted to these data. These data
show a sharp decrease in strength properties and hardness with increasing temperature, e.g.
points ‘A’ and ‘B’ in Figure 13. It also shows a small recovery in properties (after the initial
drop) once the inversion point has been passed. For example, the ultimate tensile strength
measured at room temperature after exposure at315°C for 30 minutes (denoted as ‘B’ in Figure
13) was lower than that measured after exposure at 350°C for 30 minutes (denoted as ‘C’ in
Figure 13).
11
DSTO-TR-2104
600
7075 Aluminum Alloy SST Specimens
80
PC
o
o
205 C
o
o
260 C
315 C
o
350 C
60
400
300
40
Ultimate Tensile Strength, ksi
500
Ultimate Tensile Strength, MPa
232 C
200
20
100
38
39
40
41
42
43
44
45
Electrical Conductivity, %IACS
Figure 12. Ultimate tensile strength properties at room temperature after thermal damage at indicated
conditions. The arrow indicates increasing temperature and exposure time.
200
Hardness Number (HV)
100
90
150
80
70
600
7075-T7451Aluminum Alloy SST Specimens
PC
80
Colour Code:
o
(A) 232 C, 30 minutes
500
o
205 C
77.2HRB, 449.57 MPa
o
260 C
o
232 C
o
315 C
o
60
(C) 350 oC, 30 minutes:
400
41.08HRB, 318.48 MPa
Strength, ksi
Strength, MPa
350 C
Ftu
Fty
300
40
(B) 315 oC, 30 minutes
200
30.08 HRB, 281.64 MPa
20
100
100
80
60
40
20
0
Hardness Number (HRB)
Figure 13. Tension test results at room temperature after thermal damage at indicted conditions.
Exponential curves have been fitted to these data. The direction of the arrows indicates
increasing temperature and time.
12
DSTO-TR-2104
4.2.2 Round Tension (RT) Test Specimens
The test results for the round tension test specimens are shown in Table 9 Appendix A and
Figure 14. The hardness and strength properties test results for the round tension test
specimens were higher than those measured for the sub-size tension specimens in similar
condition. The differences could be attributed to the fact that the round tension test specimens
were taken from or near to the surface of the plate used in the manufacturing of the
specimens. The hardness and strength properties of the plate are higher near the surface than
those found in the core of the plate [8]; consequently, the round tension test specimens
exhibited higher initial properties.
Hardness Number (HV)
200
150
100
90
80
70
600
PC
7075-T7351 Aluminum Alloy RT Specimens
o
205 C
500
o
260 C
80
o
232 C
o
315 C
o
60
Ftu
Fty
400
Strength, ksi
Strength, MPa
350 C
300
40
200
20
100
100
80
60
40
20
0
Hardness Number (HRB)
Figure 14. Room temperature strength properties after thermal damage at indicated conditions.
Exponential curves have been fitted to these data.
5. Discussion
The test results indicate that both aluminium alloys have qualitatively and quantitatively
comparable responses to thermal damage, and that the room temperature residual strength
properties after thermal damage can be expressed as a function of hardness number by
exponential equations.
The test data clearly shows that exposure above 205°C results in rapid deterioration of
strength properties. These changes are accompanied by measurable decrease in hardness and
an increase in electrical conductivity values that are, regardless of the exposure conditions,
indicative of the strength level of these alloys. The data also show that different combinations
13
DSTO-TR-2104
of exposure time and exposure temperature (i.e. equivalent exposure conditions) can result in
similar strength levels.
The good strength-to-weight ratio exhibited by these alloys is owed 4 to the presence of semicoherent η′ phase (and non coherent η phase). The amount, size and distribution of these
phases determine the strength properties and provide the alloys with characteristic hardness
and electrical conductivity values. However, thermal damage induces further phase
transformations, which changes the balance of these precipitates to negatively affect the
strength properties, which in turn affects the hardness and electrical conductivity values.
Nonetheless, the resulting hardness and electrical conductivity values are still characteristic of
the strength level of the alloys. Hence, hardness and electrical conductivity tests can be used
to estimate residual strength properties at room temperature after thermal damage.
The current test data show that increasing the temperature at which thermal damage was
applied resulted in faster and more significant deterioration of strength properties. This was
expected as the phase transformations (i.e. dissolution of η’ and formation of η phase)
resulting from thermal damage occur through a process of atomic diffusion (atom movement),
which is dependent on temperature. Therefore, diffusivity of the atoms will be faster at higher
temperatures (Equation 1). That is, higher exposure temperatures result in faster and more
significant deterioration of strength properties.
The diffusion rate is given by the following equation:
Equation 1
D = D0 e
⎛ E ⎞
−⎜
⎟
⎝ kT ⎠
Where D is the diffusion rate, D0 is a constant (particular to each material); E is the
activation energy for atomic movement at the conditions considered (it is not
temperature or concentration dependent), k is the gas constant and T is temperature.
Furthermore, the test results show that for longer exposure times the rate of deterioration of
strength properties slowed down as the phase transformations that drive the changes are
completed and the alloys approach a state of equilibrium at the exposure conditions. A
simplistic way to explain this behaviour is to consider only the main phase transformation (i.e.
dissolution of semi-coherent η’ -MgZn2- to form the non-coherent η -MgZn2- phases).
According to the first-order reaction rate (Equation 2), the reaction rate of the main phase
transformation will be proportional to the concentration of reactants (i.e. η’ and η) multiply
by a rate constant. Thus, as the main phase transformation progresses and the reactions at the
exposure condition are completed (η’ decreases and η increases) changes to the strength
properties will slow down in time as the alloys move towards a state of equilibrium (e.g.
annealed condition).
The First-order reaction rate equation is given by:
4 Other factors such as chemical composition and method of manufacturing also influence the
mechanical properties.
14
DSTO-TR-2104
Equation 2
−
d [c ]
= k1 × c
dt
Where c is the concentration of reactant (i.e. η’), k is the rate constant of reaction and t
is time. Equation 2 could also be written like:
Equation 3
[c] = [c]0 × e − kt
Equation 3 means that the concentration of c (i.e. η’) decreases exponentially as a function of
time. Therefore, according to Equation 1 and Equation 2, thermal damage is temperature and
time dependent and it should follow an exponential law. The test results indicate that the time
required to induce a given degree of deterioration in the strength properties is inversely
proportional to the exposure temperature.
Previous work conducted [2, 3] on thermal damage assessment shows that significant
deterioration of hardness and strength properties takes place within the first five minutes of
thermal exposure. However, in the current study an inversion point is observed after
exposure at 315°C for more than 60 minutes (A similar phenomenon was observed in the
specimens tested at 350°C). Above this exposure condition, the strength and hardness of the
alloys increased (after the initial drop), whilst at the same time the electrical conductivity
decreased. This phenomenon is attributed to a process of re-tempering [1] or re-ageing [9]
where solute elements (i.e. zinc and magnesium) that have returned to solid solution (due to
an increased solubility of solute element in the matrix resulting from exposure to elevated
temperatures) do not completely diffuse out of the matrix during rapid cooling. As a
consequence, the solute atoms that remain in solid solution produce the re-ageing or retempering effect. Hence, the increase in hardness and strength and the decrease in electrical
conductivity observed beyond the inversion point.
It is expected however that this trend of increasing strength will eventually revert as other
factors such as grain growth and coarsening of precipitates evolve. Further reduction in
strength properties will occur if formation of eutectoid structures or incipient melting at grain
boundaries takes place during thermal exposure.
In addition, it was observed that beyond the inversion point two different electrical
conductivity values could show similar hardness number and vice versa; this translated in
ambiguous strength values. That is two different strength levels could correspond to a single
electrical conductivity value; however, unlike the electrical conductivity, the difference
between two strength levels showing a similar hardness number was very small. Nonetheless,
regardless of the exposure conditions, there is only one combination of electrical conductivity
and hardness number that are characteristic of a given strength level. Therefore, both electrical
conductivity and hardness tests should be used in conjunction to determine the strength of the
alloys.
An interesting observation, which will require further analysis, is that the test results for the
ultimate tensile strength for exposures at 350°C were located above the curve fit applied to the
15
DSTO-TR-2104
Ftu data; whereas the yield strength values were below that predicted by the curve fit applied
to the Fty data.
To facilitate further analysis of the data, the test results were converted to a percentage of the
pristine strength properties at room temperature. Subsequently, exponential curves
(Equations 4 to 7) were fitted using Igor Pro 5.04B software. In addition, prediction bands
representing the region within which the results from the curve fit were expected to fall (plus
random errors) have been included; they represent a 95 % confidence level.
The following equations present the exponential curve fit that can be used to estimate the
percentage of initial strength at room temperature after thermal damage.
7050-T7451 Aluminium alloy (SST specimens):
Equation 4
Ultimate tensile Strength,
Ftu = 36.5 + 9.1× e ( 0.022×HRB )
Equation 5
Yield strength,
Fty = 20.2 + 4.9 × e ( 0.032×HRB )
7075-T7351 Aluminium alloy SST specimens:
Equation 6
Ultimate tensile Strength,
Ftu = 37.0 + 11.0 × e ( 0.021×HRB )
Equation 7
Yield strength,
Fty = 14.2 + 8.7 × e ( 0.027×HRB )
The data clearly show that both 7050-T7451 (Figure 15) and 7075-T7351 (Figure 16) aluminium
alloys have qualitatively and quantitatively similar responses to thermal damage.
Per cent of initial room temperature Strength
180
110
160
Hardness Number, HV
120
100
90
140
100
80
72
7050-T7451 Aluminium Alloy SST Specimens
Ftu
Fty
90
80
70
60
50
40
30
20
90
80
70
60
50
Hardness Number, HRB
40
30
20
Figure 15. Residual strength properties at room temperature after thermal damage in percent of initial
values
16
DSTO-TR-2104
180
110
160
Hardness Number (HV)
120
100
140
90
80
7075-T7351 Aluminum Alloy SST Specimens
Per cent of initial room temperature Strength
100
Ftu
Fty
90
80
70
60
50
40
30
20
90
80
70
60
50
40
30
20
Hardness Number (HRB)
Figure 16. Residual strength properties at room temperature after thermal damage in percent of initial
values
Regarding the results for the round tension and sub-size tension specimens, the differences in
the results were attributed to variations in properties within the plates (e.g. specimens that
were taken close to or from the core of the plate presented lower strength, lower hardness and
higher electrical conductivity). However, the most important observation regarding the
differences in the test results is that both sets of results showed similar (and almost identical)
rates of strength deterioration. For example in the case of 7050-T7451 aluminium alloy, curve
fits applied to the round tension and sub-size tension test specimens were almost the same
despite the initial higher hardness (and strength) of the sub-size tension specimens (Figure
17). Similar results were observed for 7075-T7351 aluminium alloy in the temperature range
tested (Figure 18).
These findings suggest that the rate of deterioration due to thermal damage is almost
independent of the initial condition for these two alloy tempers.
17
DSTO-TR-2104
180
160
140
120
Hardness Number (HV)
100
90
80
72
110
Per cent of inital room temperature Tensile Strenght
7050-T7451 Aluminum Alloy Tension Specimens
100
SSTspecimen Ftu
SSTspecimen Fty
90
RT specimen Ftu
RT specimen Fty
80
70
60
50
40
30
20
80
60
Hardness Number (HRB)
40
20
Figure 17. Comparison of residual strength properties of sub-size tension (SST) and round tension
(RT) test specimen at room temperature after thermal damage. Markers have been added for
better visualisation.
Hardness Number (HV)
180
160
140
120
100
90
80
110
7075-T7351 Aluminum Alloy Tension Specimens
Per cent of initial room temperature Strength
100
90
SST specimen Ftu
RT specimen Ftu
80
70
60
50
SST specimen Fty
RT specimen Fty
40
30
20
80
60
Hardness (HRB)
40
20
Figure 18. Comparison of residual strength properties of sub-size tension (SST) and round tension
(RT) test specimen at room temperature after thermal damage. Markers have been added for
better visualisation.
18
DSTO-TR-2104
6. Further Comments
The data on the effects of thermal damage on the strength properties of 7050-T7451 and 7075T7351 aluminium alloys presented in this report assume uniform thermal exposure of an
affected area, which in most instances of thermal damage of structures and components is not
the case. Therefore, predictions based on these data might be conservative. However, a
conservative approach is necessary when thermal damage assessment is performed as in most
instances the exposure conditions of the affected areas are unknown.
Furthermore, partial recovery of properties within a thermally damaged area should not be
interpreted as a partial recovery of all properties; instead, it should be considered as an
indication of possible severe thermal damage. The difficulty in attempting an estimation of
residual strength beyond the inversion point is that other factors such as grain growth,
precipitation of particles at grain boundaries, formation of eutectic structures and ultimately
incipient melting at grain boundaries (if present) cannot be accounted for by hardness or
electrical conductivity tests alone. Consequently, any prediction based on these tests might
produce results that overestimate the strength of affected areas.
In addition to the obvious concerns regarding the effects of thermal damage on the strength of
these alloys, other factors such as creep rupture and creep properties as well as corrosion
resistance of these alloys might also be affected (these aspects are not part of the DSTO test
program). Fatigue life and fracture toughness are also affected.
7. Conclusions
Based on the tests conducted on thermally damaged specimens made from of 7050-T7451 and
7075-T7351 aluminium alloys, it is concluded that:
1. Both alloys showed qualitatively and quantitatively similar response to thermal
damage.
2. Regardless of the thermal exposure conditions, the level of deterioration in the
strength properties caused by thermal damage is characterised by a unique
combination of hardness number and electrical conductivity values that can be used to
estimate the remaining strength level.
3. The residual strength of these alloys at room temperature after thermal damage can be
expressed as a function of hardness number by exponential equations.
4. There was an increase in strength, measured at room temperature, after the initial
drop was recorded for both materials after exposure at 315°C for more than
60 minutes. This point marks the beginning of a partial recovery of strength. A similar
phenomenon was observed in specimens tested at 350°C. It is however expected that
this trend will revert, as other factors that affect the strength of the alloy evolve (e.g.
precipitation of particles at grain boundaries).
5. Different combinations of exposure temperature and time (i.e. equivalent exposure
conditions) can result in similar strength levels.
19
DSTO-TR-2104
6. The time required for changes in strength properties is inversely proportional to the
temperature.
8. Acknowledgement
The authors would like to acknowledge the technical support and contribution of DSTO staff
and in particular to Nicholas Athiniotis, Simon Barter, Charles Brady, Greg Cunningham,
Noel Goldsmith, Bruce Grigson, David Holmes, Robert Pell, Kevin Phibbs and Michael Ryan.
Without their support and collaboration this work could not have come to fruition.
9. References
1. Hagemaier, D, ‘Evaluation of Heat Damage to Aluminium Aircraft Structures’. Materials
Evaluation, Vol. 40, No. 9, p. 962-969, Aug. 1982.
2. Holmes, D, ‘Assessing properties of heat damaged aluminium 7075-T73’. Aeronautical
Engineering Support Facility, Australia, 1996. Directorate General of Technical
Airworthiness, Royal Australian Air Force.
3. Clark, B, ‘Overaging of alloys used in airframe construction resulting from accidental
exposure to heat’. University of Ballarat, Nov. 1997.
4. Department of Defence. Military Specification MIL-H6088G (1991), ‘Heat Treatment of
Aluminium Alloys’, Department of Defence United States of America.
5. Calero, J. (2006), ‘Study of the Effects of Thermal Damage on the Fatigue Life of AA7050T7451 Aluminium Alloy’. International Conference on Structural Integrity and Failure
(SIF2006). Melbourne, Australia.
6. Calero, J. (2007), ‘Effects of Thermal Damage on the Mechanical Properties of
7050-T7451 Aluminium Alloy’. International Committee on Aeronautical Fatigue (ICAF
2007), 24th ICAF Symposium. Naples, Italy.
7. ASTM B 557M – 94, ‘Standard Test Methods of Tension Testing Wrought and Cast
Aluminium – and Magnesium – Alloy Products’.
8. Barter, S. Air Vehicles Division, Defence Science and Technology Organisation Melbourne,
Australia, not published.
9. Wu X. J., Koul A. K., Zhao L, ‘A New Approach to Heat Damage Evaluation for 7XXX
Aluminium Alloy’, Canadian Aeronautics and Space Journal, volume 42, No. 2, 1996, pp
93-101.
20
DSTO-TR-2104
Appendix A: Tables
Table 6.
Test results for 7050-T7451 aluminium alloy sub-size tension (SST) test specimens
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
---
40.50
89.4
89.0
89.8
536
485
17.20
---
40.80
87.7
87.6
87.9
519
464
13.72
205
30
41.55
84.6
84.1
84.9
510
429
18.8
205
30
41.50
84.4
83.6
85.2
494
425
17.1
205
30
41.50
83.7
83.4
83.9
497
421
14.9
205
60
40.90
84.4
83.9
84.9
486
427
16.13
205
60
40.90
83.2
82.9
83.6
493
429
13.89
205
60
41.43
81.6
80.8
82.5
483
412
17.73
205
300
44.10
69.0
68.4
69.5
415
316
17.4
205
300
44.60
68.7
67.6
70.1
412
313
16.5
205
300
44.50
66.7
66.0
67.1
402
308
17.8
232
10
41.10
84.7
84.0
85.3
532
456
13.4
232
10
41.50
80.9
80.2
81.7
502
420
14.5
232
10
42.70
75.1
73.5
75.7
458
362
14.7
232
30
40.20
84.9
84.8
85.0
506
436
19.10
232
30
42.70
75.7
74.9
76.2
441
353
17.10
232
30
42.70
72.8
71.9
73.3
421
327
18.68
232
60
43.10
73.6
73.2
73.9
431
337
19.63
232
60
43.10
72.9
72.3
73.4
420
327
16.51
232
60
43.60
70.4
70.0
70.8
409
311
18.87
232
300
45.50
56.5
55.8
56.9
353
244
19.63
232
300
45.50
56.1
55.6
56.5
349
239
19.51
232
300
45.55
55.4
54.2
55.9
348
240
17.20
260
10
43.20
71.8
70.4
72.9
431
329
19.1
260
10
43.50
70.2
69.2
71.3
407
305
17.8
260
10
43.50
68.8
68.1
69.4
406
304
17.8
260
30
44.10
56.6
55.9
57.0
363
261
17.27
260
30
44.30
55.8
55.4
56.2
357
255
15.78
260
30
44.60
54.8
54.6
55.0
354
256
17.38
260
60
45.20
55.6
54.6
56.6
346
229
19.4
260
60
44.60
53.1
51.7
53.9
346
225
18.9
Exp Temp (ºC)
Pristine Condition
(PC) - Room temp
Pristine Condition
(PC) - Room temp
(Continued)
21
DSTO-TR-2104
Table 6.
Test results for 7050-T7451 aluminium alloy SST test specimens (Continued)
Exp Temp
(ºC)
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
260
300
45.50
39.1
38.2
39.7
296
179
19.20
260
300
45.60
38.9
37.9
39.9
300
186
19.91
260
300
45.70
37.3
36.7
37.7
297
182
18.90
315
10
45.40
36.6
36.1
36.8
290
174
20.19
315
10
45.60
36.6
36.2
37.0
289
173
19.69
315
10
44.53
35.5
34.5
36.1
289
167
18.09
315
30
44.50
32.4
31.8
33.1
286
160
18.38
315
30
44.45
31.7
31.0
32.5
287
161
20.77
315
315
315
30
60
60
45.20
44.60
45.40
31.0
28.2
23.4
30.8
27.7
22.6
31.5
28.7
24.3
279
290
271
158
159
150
19.80
18.32
19.82
315
60
45.50
21.9
20.3
24.3
264
148
17.99
315
300
43.63
40.1
39.2
40.6
334
179
16.52
315
300
43.63
38.2
37.2
38.7
321
174
315
300
45.00
21.7
21.2
21.8
274
145
18.57
350
10
43.10
45.2
44.4
45.9
351
196
13.06
350
10
43.70
40.3
38.9
41.6
330
179
14.58
350
10
45.00
24.5
23.9
25.1
274
148
19.53
350
30
42.70
51.9
51.4
52.1
359
190
17.32
350
30
42.90
49.8
49.5
50.4
341
177
18.76
350
30
44.70
31.8
31.2
32.5
288
145
22.93
350
60
43.85
37.6
35.0
40.1
306
157
17.8
350
60
44.75
36.1
35.5
36.7
298
173
19.5
350
300
41.50
58.7
58.1
59.1
371
200
20.77
350
300
41.20
58.1
57.1
59.2
381
210
19.73
350
300
41.70
56.6
56.1
57.0
370
199
14.30
Table 7.
14.47
Test results for 7050-T7451 aluminium alloy round tension (RT) test specimens
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
---
39.9
84.4
82.8
86.8
489
460
13
---
40.3
83.0
82.2
83.4
491
418
13
---
40.0
82.7
82.2
83.0
483
413
13
205
10
40.1
83.6
82.9
84.1
484
412
14
205
10
39.8
83.1
82.2
84.1
478
403
13
205
10
40.1
82.4
81.6
83.0
487
415
13
205
60
39.9
80.8
79.3
81.6
478
402
14
Exp Temp (ºC)
Pristine Condition
(PC) - Room temp
Pristine Condition
(PC) - Room temp
Pristine Condition
(PC) - Room temp
(Continued)
22
DSTO-TR-2104
Table 7.
Test results for 7050-T7451 aluminium alloy RT test specimens. (Continued)
Exp Temp
(ºC)
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
205
60
40.1
80.7
80.5
81.0
468
387
14
205
60
40.3
78.6
78.2
79.1
458
373
15
232
10
40.1
82.4
82.0
82.8
484
411
15
232
10
39.9
82.3
81.8
83.0
486
414
15
232
10
39.7
79.2
78.5
79.5
471
392
15
232
60
41.6
69.0
68.9
69.0
398
298
17
232
60
42.0
65.0
64.5
65.3
380
276
15
232
60
41.9
64.8
64.1
65.8
382
279
17
260
10
42.1
66.1
65.9
66.4
388
286
17
260
10
42.0
65.9
65.6
66.1
383
280
17
260
60
42.8
51.8
51.0
52.4
324
209
19
260
60
43.0
50.3
49.6
50.9
323
208
13
260
60
42.9
49.1
48.8
49.4
322
206
13
315
60
45.1
27.5
25.6
29.7
266
142
12
315
60
45.6
26.7
26.5
26.8
259
140
12
315
60
42.6
26.6
25.1
28.0
265
133
13
350
30
41.3
34.8
34.0
35.4
290
152
13
350
30
41.5
33.7
32.5
35.0
298
148
14
350
30
41.8
29.0
28.8
29.3
288
141
14.0
Table 8.
Test results for 7075-T7351 aluminium alloy sub-size tension (SST) test specimens
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
---
40.0
84.9
84.7
85.3
499
424
16
---
40.0
84.7
83.7
85.8
497
422
15
---
40.2
84.1
83.5
84.6
496
418
15
205
30
39.7
81.9
81.3
82.6
482
397
17.2
205
30
39.7
81.5
81.2
81.8
481
390
17.0
205
60
39.9
81.7
81.3
82.1
481
403
17.32
205
60
39.9
80.2
79.8
80.4
468
385
16.35
205
60
40.7
78.2
77.8
78.4
452
366
15.89
205
300
42.7
68.9
68.4
69.7
405
293
16.7
Exp Temp (ºC)
Pristine Condition
(PC) - Room temp
Pristine Condition
(PC) - Room temp
Pristine Condition
(PC) - Room temp
(Continued)
23
DSTO-TR-2104
Table 8.
Test results for 7075-T7351 aluminium alloy SST test specimens (Continued).
Exp Temp
(ºC)
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
205
300
42.7
68.6
67.9
69.2
408
295
16.4
205
300
42.7
68.4
67.7
69.3
403
291
18.5
232
10
40.7
77.1
76.4
77.5
453
350
17.2
232
10
40.7
75.9
75.4
76.3
451
347
15.0
232
30
40.4
80.3
79.2
80.9
472
387
16.27
232
30
40.4
79.2
78.0
80.1
463
380
15.99
232
30
40.7
77.2
76.8
77.5
450
357
16.60
232
60
40.6
77.3
75.7
78.4
445
350
13.13
232
60
40.9
76.7
75.4
77.8
443
347
16.71
232
60
41.1
74.6
73.9
75.3
431
330
16.69
232
300
43.2
52.5
52.3
52.6
336
221
17.37
232
300
43.2
51.9
50.7
52.6
335
220
16.75
232
300
43.2
51.6
51.1
52.2
335
220
17.31
260
10
41.5
68.1
67.6
69.2
404
288
16.8
260
10
41.5
68.0
67.7
68.4
403
287
17.0
260
10
41.5
62.4
61.7
62.9
384
262
16.4
260
30
42.2
54.0
53.6
54.5
346
229
17.39
260
30
42.2
54.0
53.2
54.4
343
225
17.52
260
30
42.6
53.1
52.4
53.6
343
227
17.25
260
60
43.1
51.0
50.5
51.2
337
210
17.0
260
60
43.0
48.9
48.4
49.2
336
207
17.2
260
60
43.0
48.6
47.3
50.1
331
206
17.0
315
10
42.3
33.1
32.7
33.5
292
157
19.68
315
10
42.4
32.5
31.7
33.3
286
157
19.13
315
10
42.4
30.9
30.4
31.4
238
151
19.47
315
30
42.1
32.5
31.5
33.9
291
153
20.10
315
30
42.5
30.1
29.5
30.5
282
148
20.15
315
30
42.7
30.0
29.5
30.6
283
149
20.56
315
60
41.8
37.6
37.1
38.2
310
158
19.28
315
60
41.8
35.1
28.1
37.9
309
157
21.44
315
60
42.5
29.8
29.1
30.3
283
145
21.39
350
10
40.9
44.9
44.2
46.3
331
169
19.98
350
10
40.8
44.3
43.9
44.8
330
169
20.27
(Continued)
24
DSTO-TR-2104
Table 8.
Test results for 7075-T7351 aluminium alloy SST test specimens (Continued)
Exp Temp
(ºC)
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
350
10
41.1
43.6
43.2
43.9
331
170
20.39
350
30
41.3
41.7
40.9
42.6
321
162
19.37
350
30
41.3
41.1
40.6
41.6
318
161
20.23
350
30
41.6
36.3
35.8
36.8
305
154
20.76
350
60
41.2
43.2
42.1
44.1
334
168
19.7
350
60
41.1
37.9
37.8
38.1
312
152
19.8
Table 9. Test results for 7075-T7351 aluminium alloy RT tension test specimens
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
---
40.3
88.7
88.5
88.9
525
480
15.9
---
40.9
86.7
86.3
87.0
513
466
12.5
---
41.0
86.3
86.0
86.9
518
465
13.5
205
10
40.2
88.4
88.0
89.2
520
476
15.7
205
10
40.1
87.8
87.3
88.3
520
477
14.9
205
10
40.0
86.9
86.4
87.4
513
465
15.7
205
60
41.7
80.9
80.7
81.2
470
400
15.2
205
60
41.3
80.6
80.5
80.8
482
416
11.2
205
60
42.5
76.3
75.8
76.6
457
389
12.7
232
10
40.0
87.1
86.3
87.5
516
470
15.6
232
10
40.8
85.7
85.0
86.2
516
460
12.8
232
10
40.9
82.5
82.5
82.6
492
430
12.3
232
60
42.2
77.8
77.5
78.4
454
377
13.2
232
60
42.9
74.1
73.9
74.2
432
348
14.0
232
60
43.2
72.2
71.8
72.7
417
330
260
10
43.2
74.5
74.2
74.8
423
336
16.7
260
10
41.3
70.3
69.8
71.0
411
313
14.5
260
10
43.8
69.4
68.2
70.3
408
324
14.0
260
60
45.0
56.8
56.5
56.9
336
228
16.3
260
60
45.1
56.5
56.0
57.2
338
230
16.7
260
60
45.3
51.6
51.3
52.1
333
237
15.1
315
10
42.8
31.9
30.7
32.6
278
152
16.2
Exp Temp (ºC)
Pristine Condition
(PC) - Room temp
Pristine Condition
(PC) - Room temp
Pristine Condition
(PC) - Room temp
(Continued).
25
DSTO-TR-2104
Table 9.
Test results for 7075-T7351 aluminium alloy RT tension test specimens. (Continued)
Exp Temp
(ºC)
Exp Time
(minutes)
%ICAS
Hardness
(HRB)
HRB
MIN
HRB
MAX
Ftu
(MPa)
Fty
(MPa)
Elongation,
2%
315
10
42.9
31.5
30.3
33.3
277
151
16.0
315
60
44.9
28.8
28.2
29.4
269
145
15.1
315
60
45.1
28.7
28.1
29.5
265
144
16.9
315
60
44.7
28.3
27.3
29.8
273
147
15.7
350
30
43.5
41.2
40.8
41.5
321
162
18.8
350
30
43.6
41.1
40.4
42.3
334
173
15.2
350
30
43.3
41.0
39.9
41.8
322
163
20.3
26
Page classification: UNCLASSIFIED
DEFENCE SCIENCE AND TECHNOLOGY
ORGANISATION
DOCUMENT CONTROL DATA
2. TITLE
1. PRIVACY MARKING/CAVEAT (OF DOCUMENT)
3. SECURITY CLASSIFICATION (FOR UNCLASSIFIED REPORTS THAT ARE
LIMITED RELEASE USE (L) NEXT TO DOCUMENT CLASSIFICATION)
Effects of Thermal Damage on the Strength Properties of
7050-T7451 and 7075-T7351 Aluminium Alloys
Document
Title
Abstract
(U)
(U)
(U)
4. AUTHOR(S)
5. CORPORATE AUTHOR
Jaime Calero and Suzana Turk
DSTO Defence Science and Technology Organisation
506 Lorimer St
Fishermans Bend Victoria 3207 Australia
6a. DSTO NUMBER
6b. AR NUMBER
6c. TYPE OF REPORT
7. DOCUMENT DATE
DSTO-TN-2104
AR-014-106
Technical Report
February 2008
8. FILE NUMBER
9. TASK NUMBER
10. TASK PONSOR
11. NO. OF PAGES
12. NO. OF REFERENCES
2006/1056002
AIR 06/022
DGTA
26
9
13. URL on the World Wide Web
14. RELEASE AUTHORITY
http://www.dsto.defence.gov.au/corporate/reports/DSTO-TR2104.pdf
Chief, Air Vehicles Division
15. SECONDARY RELEASE STATEMENT OF THIS DOCUMENT
Approved for public release
OVERSEAS ENQUIRIES OUTSIDE STATED LIMITATIONS SHOULD BE REFERRED THROUGH DOCUMENT EXCHANGE, PO BOX 1500, EDINBURGH, SA 5111
16. DELIBERATE ANNOUNCEMENT
No Limitations
17. CITATION IN OTHER DOCUMENTS
18. DSTO
Yes
Research Library Thesaurus
Thermal damage, 7050 aluminium alloy, 7075 aluminium alloy, hardness, electrical conductivity, strength
19. ABSTRACT
This report presents experimental test data that quantify the effects of thermal damage on the strength properties of 7050-T7451 and
7075-T7351 aluminium alloys. The test results indicate that there is a direct relationship between hardness and strength properties that
can be used to determine residual strength of these alloys at room temperature after thermal damage. This relationship can be expressed
as a function of hardness number by the use of exponential equations.
Page classification: UNCLASSIFIED