MFET 3451
Age Hardening of Aluminum Alloys
Experiment # 7
Objective:
a) To perform age hardening or precipitation hardening of Aluminum alloys.
b) To learn the effects of age hardening on the hardness of Aluminum alloys.
Equipment:
Heat treatment furnace with proper controls for age hardening, suitable tongs, appropriate
quenching media, and consumables as needed.
Materials:
The three alloys will be studied in this experiment are among the most widely used heat
treatable aluminum alloys. They represent three different alloys:
a) 2024 Al (Al-4.5Cu-1.5Mg-0.6Mn),
b) 6061 Al (Al-1Mg-0.6Si-0.25Cu- 0.2Cr), and
c) 7075 Al (Al-5.6Zn-2.5Mg-1.6Cu-0.3Cr).
Procedure:
Step 1: Identify the different samples using proper identification methods.
Step 2: Measure the Rockwell hardness values of all the as-received samples.
Step 3: This step is called solution treatment. This process involves treating alloys
between solvus and solidus temperature (Figure 1) and held there until (at least 1hr) a
uniform solid-solution structure is obtained.
Step 4: This step consists of quenching the solution treated alloys rapidly in water at
room temperature.
Step 5: Measure the hardness of the quenched samples and tabulate as follows:
Alloy
2024
6061
7075
Solution
treatment
temperature
495 ºC
525 ºC
490 ºC
Rockwell Hardness
As- Received
Solution
Treated
Step 6: This step involves aging the alloys both artificially and naturally. Naturally aging of
alloys involves allowing the quenched samples to age on their own and artificial aging involves
reheating the quenched samples.
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This Session:
Prior to the session, the instructor should place four pieces of
aluminum alloy (suggested dimensions)25
mm x
25mm x 2mm) in
the
°C solution-treating furnace. The pieces should be in
the furnace for about one hour. Begin the session by acquainting
the students with the nomenclature for aluminum alloy tempers 0, T3, T4 and T6. Then take the aluminum alloy pieces from the
furnace and immediately quench each one in room temperature
water. As promptly as possible,
one piece should be put into the freezer until the next session,
four piece should be put into the 220°C furnace.
four pieces should be put into the 175°C furnace.
one piece will be used to establish the hardness in the solution
treated condition and the initial portion of the natural age
hardening response.
After quenching the last piece, carefully grind opposite
surfaces flat with an abrasive belt grinder. Then measure the
hardness of the sample in at least three places. Record the
elapsed time between quenching and hardness testing, which
should be no more than five minutes. Continue to measure the
hardness of the piece in at least three places at time intervals
of 15, 30,45, 60 minutes.
after quenching. This piece should be stored by the instructor
at room temperature until the next session.
Remove one sample from each of the furnaces after soaking times
of 15, 30, 45 and 60 minutes. The samples can be cooled in
water. Again, carefully grind opposite surfaces flat with an
abrasive belt.
Measure the hardness of each sample in at least three places.
cold roll one piece about 5%, measure its thickness after
rolling, cut or saw it into four pieces and put all of them into
the 220°C furnace,
cold roll one piece about 5%, measure its thickness after
rolling, cut or saw it into four pieces and put all of them into
the175°C furnace,
cold roll one piece about 5%, measure its thickness after
rolling, grind opposite faces flat and then measure its hardness
in at least three places; make subsequent hardness measurements
at intervals of 15, 30, 45 and 60 minutes after cold rolling.
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Step 7: Measure the hardness values of these samples and tabulate as follows:
Rockwell Hardness AL
Aging time
(hrs)
As Is
495 ºC
220 ºC
175 ºC Cold
220 /175
Natural Freezer
0
15 minutes
30 minutes
45 minutes
1 Hour
Assignment:
1. Are the hardness values comparable to theoretical values?
2. Plot the hardness data and compare the hardness for the different aging periods.
3. Is their any relation between
a) aging temperature and peak hardness values,
b) alloy composition and peak hardness
c) time required to achieve peak hardness at different aging temperatures.
4. What other properties other than hardness is effect by precipitation hardening of Al alloys
Table 1-2.-Designations for Aluminum Alloy Groups
Aluminum- 99.0 percent minimum and greater ………………………………………1xxx
Aluminum alloy, grouped by major alloying element:
Copper……………………………………………………………………………………2xxx
Magnanese………………………………………………………………………..……...3xxx
Silicon……………………………………………………………………………………4xxx
Magnesium……………………………………………………………………………….5xxx
Magnesium and silicon…………………………………………………………………...6xxx
Zinc……………………………………………………………………………………….7xxx
References:
1. Heat Treating, Metals Handbook, ninth edition, ASM International, Metals Park, Ohio,
Volume 4, (1990).
2. Aluminum Standards and Data, Seventh Edition, The Aluminum Association, Inc.,
(1982).
3. “Aluminum and Aluminum Alloys,” ASM International, 1993.
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Figure 1: Al-Cu phase diagram (Al rich, partial),
showing three steps in precipitation hardening and the
microstructures that are produced
Figure 2: Al-Cu phase diagram
showing GP Zones
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