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STUDY OF THE EFFECT OF AGING CONDITION ON STRENGTH AND
HARDNESS OF 6063-T5 ALLOY
Supervised by : Dr. G.I.P. De Silva
Presented by : E.M.A.N. Ekanayaka S.A.D.T. Dharmarathna
INTRODUCTION
Aluminium - The most abundant metal in the earth crust
• 8% by weight of the earth’s solid surface
Properties - Durability, light weight, good extrudabilityand surface finish
Pure metal and the alloy used as alternatives for other metals (ferrous and non-ferrous), ceramics and wood
Sri Lankan demand
• Structural applications: Window and Door Frames, Partitioning, L bars, U bars
2
ALUMEX (PVT) LTD.
Project was industrially focused on “Alumex”
Product: Extruded Aluminium articles
Raw material: 6063-T5 Aluminium alloy
3
ISSUES
Production cannot meet the present increased demand
Relatively high cost of products
4
PRODUCTION PROCESS
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Casting
Homogenizing
Extrusion
Age Hardening
Surface Treatments
REMEDY
Reduction of time in the Age Hardening process
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OBJECTIVES
To reduce the Age Hardening Time
To reduce the Energy Consumption
To upgrade the Mechanical Properties
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LITERATURE REVIEW
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6063-T5 Aluminium alloy
6063 Age Hardenable Aluminium alloy
• Main alloying elements: Mg (0.2 ~ 0.6 wt%)
Si (0.45 ~ 0.9 wt%)
T5 - Cooled from an elevated temperature andartificially aged
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6063-T5 Aluminium alloy
Second Phase: Mg2Si
Solid solubility of Mg2Si decreases from 1.85 wt. %
at the eutectic temperature of 595 C
Al-Mg2Si quasi binary system forms10
Age hardening
Maximum hardness is achieved if the precipitates canresist cutting by dislocations, and are too close topermit by-passing of dislocations.
Strengthening a metal by introducing small particles of another phase which barriers dislocations motion
Cutting through:When the precipitates are too small
Bowing and By pass:When precipitates are too strong to be cut and inter-particle space become large
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The Age Hardening Process
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SSSS
Solution treatment
Age hardening treatment
Al-Mg2Si quasi binary system
GP zones – First form of precipitates (unstable) Needle Shaped with the long axis along [100] of the matrix
Sequence of precipitates in Al-Mg2Si
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Al-Mg2Si quasi binary system
Sequence of precipitates in Al-Mg2Si
β΄ phase – Developed rod shape with Hexagonal crystal structure
Maximum hardness14
Al-Mg2Si quasi binary system
Sequence of precipitates in Al-Mg2Si
β phase - Equilibrium phase with FCC crystal structure
Alloy is over aged – Hardness decreases
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Al-Mg2Si quasi binary system
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Closely spaced fine precipitates
• Resist dislocation Bowing and By pass
Strong large precipitates
• Resist cutting by dislocations
This is called a Bimodal Precipitate Structure
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Closely Spaced Fine Precipitates
Strong Large Precipitates
Increased Hardness+ =
CONCEPT
Two Step Aging Process
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Homogeneous Nucleation of a Solute Cluster
r = radius of solute cluster
ΔG = free energy needed to form a spherical
cluster of radius r
GV = change in free energy per unit volume
σ = surface free energy per unit area
rc = critical radius of the cluster
Gibbs-Thompson equation
S = Amount of super saturation at a particular temperature
K = Temperature dependent constant ( K 1/ T )
rc= Critical radius of a cluster at the relevant temperature
When T increases, rc increases
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At temp. T1 clusters nucleate and
grow - Size distribution: rmin – rmax
When temp. is raised from T1 to T2,
critical radius is raised from rc1 to rc2
If cluster radius r > rc2, the cluster will
survive and continue to grow
If cluster radius r < rc2, the cluster will
be unstable and will dissolve. Butre-nucleation may occur.
This results a Bimodal PrecipitateStructure with both closely spacedfine precipitates + strong largeprecipitates, which results betterMechanical Properties.
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Industrially Practiced Age Hardening Process
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Solution treatment
Age hardening treatment
Process was re-performed within the laboratory
Results were used as reference values
•Measured Hardness(HV) – 47.05
•Total Time (Age Hardening) – 270 min
Parameters Varied During the Process
1st step temperature - T1
Time to reach the 1st step temperature - t1
Soaking time in the 1st temperature - t2
2nd step temperature - T2
Time to reach the 2nd step temperature - t3
Soaking time in the 2nd temperature – t423
T2
T1
t5t4t3t2t1
Temperature (oC)
Time (min)
LIMITATIONS
Furnace Limitation• The industrially acceptable range: 150oC to 250oC
Energy Consumption
Total Time Consumption• Below 270 min
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CONSTANTSTime to reach the 1st step temperature: t1
• 60 minutes
2nd step temperature: T2
• 225oC
Time to reach the 2nd step temperature: t3
• 30 minutes
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T2
T1
t5t4t3t2t1
Temperature (oC)
Time (min)
STAGE 1 - VARIABLES1st step temperature: T1
• Altered within150oC-200oC
Soaking time in the 1st temperature: t2• Varied from 45 min- 90 min for each set of temperatures
Soaking time in the 2nd temperature: t4• Varied Combinations-15 min and 30 min
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T2
T1
t5t4t3t2t1
Temperature (oC)
Time (min)
All Specimens were Solution Treated
• At 540oC for 3 hours
• To remove age hardening imposed
• Dissolve all precipitates
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Muffle Furnace
A set of combinations among the above variables were developed
Heat treatments were performed using the Super C furnace for 2 samples per combination.
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Super C Furnace
Hardness was tested using Vickers Hardness tester
• 3 per sample 6 per combination
• Average was recorded
Optimum suitable parameters determined using hardness obtained
29Vickers Hardness Tester
Aging Time and Temperature Combinations
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1st step 2nd step Hardness
(HV)Temperature Time Temperature Time
150oC 60 min 225oC 15 min 37.85
150oC 90 min 225oC 15 min 38.25
175oC 45 min 225oC 15 min 39.10
175oC 60 min 225oC 15 min 41.68
175oC 75 min 225oC 15 min 47.58
175oC 90 min 225oC 15 min 45.93
200oC 60 min 225oC 15 min 35.05
200oC 90 min 225oC 15 min 37.87
t4 – maintained as 15 minT1 – varied from 150oC to 200oC
T2
T1
t5t4t3t2t1
Tem
per
atu
re (o
C)
Time (min)
Hardness – Not Satisfactory
31
32
t4 – maintained as 30 min
T1 – varied from 150oC to 200oC
T2
T1
t5t4t3t2t1
Tem
per
atu
re (o
C)
Time (min)
1st step 2nd stepHardness
(HV)Temperature Time Temperature Time
150oC 60 min 225oC 30 min 41.47
150oC 90 min 225oC 30 min 41.25
175oC 45 min 225oC 30 min 40.92
175oC 60 min 225oC 30 min 51.68
175oC 75 min 225oC 30 min 52.05
175oC 90 min 225oC 30 min 43.78
200oC 60 min 225oC 30 min 36.42
200oC 90 min 225oC 30 min 40.62
Reference Hardness (HV) – 47.05
DERIVATION
1st Step Temperature (T1) : 175oC
1st Step Soaking Time (t2) : 60 min
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Rejections
• 150oC – Low hardness in acceptable time duration
• 200oC – Higher energy consumption
Current Status 1st step temperature : 175oC
Time to reach the 1st step temperature : 60 min
Soaking time in the 1st temperature : 60 min
2nd step temperature : 225oC
Time to reach the 2nd step temperature : 30 min
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225
175
30t4306060
Tem
per
atu
re (
oC
)
Time (min)
35
2nd step soaking time “t4” was altered
• 0 ~ 60 min – 10 min intervals
Different sets of combinations were developed
Samples prepared as standard tensile test specimens
Tensile Test Sample
1.72mm(Gauge Length)
150 mm
14mm
66 mm
STAGE 2
Heat Treatment - Super C• 2 specimens per combination
Hardness - Vickers Hardness Tester• 3 per sample 6 per combination
• Average was recorded
Tensile Strength – Tensile Testing Machine
36Tensometer
Combinations and Results for varied “t4”
37
Sample noHeat Treatment
t4 (min)Hardness
(HV)
Tensile Strength
(N/mm2)1st Step 2nd Step
1 Reference _ 47.05 228.41
2 175oC - 60 min 225 oC - 0 min 0 45.08 170.27
3 175oC - 60 min 225 oC - 10 min 10 45.38 182.72
4 175oC - 60 min 225 oC - 20 min 20 46.83 199.34
5 175oC - 60 min 225 oC - 30 min 30 49.13 228.41
6 175oC - 60 min 225 oC - 40 min 40 51.10 240.86
7 175oC - 60 min 225 oC - 50 min 50 47.88 240.86
8 175oC - 60 min 225 oC - 60 min 60 45.33 232.56
Graph of Hardness Vs “t4” value
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45.08 45.38
46.83
49.13
51.10
47.88
45.33
32.00
37.00
42.00
47.00
52.00
57.00
0 10 20 30 40 50 60
Har
dn
ess
(H
V)
t4 value (min)
47.05
Graph of Strength Vs “t4” value
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170.27
182.72
199.34
228.41
240.86 240.86
232.56
100.00
120.00
140.00
160.00
180.00
200.00
220.00
240.00
260.00
0 10 20 30 40 50 60
Ten
sile
Str
en
gth
(N
/mm
2)
t4 value (min)
228.41
Theoretically
• Absorbed heat energy (E) = mcE= Heat energy
m = Mass of samples
c = Specific Heat Capacity
= Temperature Difference
• Since m and c are constant
• Energy Ratios = Ratio of areas under the graphs
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Temperature (oC)
Time (min)
Energy Comparison
EFFECTIVENESS – Varied “t4”
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Sample noHeat Treatment
t4 (min)Total Time
(min)
% Time
Saving
% Energy
Saving1st Step 2nd Step
1 Reference_
270 0 0
2 175oC - 60 min 225oC- 0 min 0 180 33.33 45.59
3 175oC - 60 min 225oC- 10 min 10 190 29.63 39.96
4 175oC - 60 min 225oC- 20 min 20 200 25.93 34.33
5 175oC - 60 min 225oC- 30 min 30 210 22.22 28.71
6 175oC - 60 min 225oC- 40 min 40 220 18.52 23.08
7 175oC - 60 min 225oC- 50 min 50 230 14.81 17.45
8 175oC - 60 min 225oC- 60 min 60 240 11.11 11.82
Optimum was selected considering above results
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225
175
3040306060
Tem
per
atu
re (o
C)
Time (min)
205
90
Tem
per
atu
re (o
C)
Time (min)30150
Developed Process Process at Alumex
Hardness (HV) = 51.10
Tensile Strength (N/mm2) = 240.86
Total Time (min) = 220
Hardness (HV) = 47.05
Tensile Strength (N/mm2) = 228.41
Total Time (min) = 270
Microstructure Observations
Microstructure • Selected sample and reference
• Viewed using Metallurgical microscope (X200)
• Idea about grain size
43
Metallurgical Microscope
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After optimized Two Step Aging Treatment
Polishing Agent: Polycrystalline Diamond Powder
Etchant: 5% HNO3 + 2% HF Solution
Microstructure Observation
After “Alumex” Practiced Aging Treatment
Polishing Agent: Polycrystalline Diamond Powder
Etchant: 5% HNO3 + 2% HF Solution
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225
175
3040306060
Tem
per
atu
re (
oC
)
Time (min)
PROGRESS
Property / parameter Practiced Process Developed Process
Hardness (HV) 47.05 51.10
Tensile Strength (N/mm2) 228.41 240.86
Total Time (min) 270 220
Time Saving (min) _ 50
% Time Saving _ 18.52
% Energy Saving _ 23.08
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CONCLUSION
Considering Production Rate, Production Cost andEnhanced Mechanical Properties the following AgeHardening Treatment is recommended.
225
175
3040306060
Tem
per
atu
re (
oC
)
Time (min)
THANK YOU
47