Metalllurgy question

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Mr Ron
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Metalllurgy question

Post by Mr Ron » Fri Sep 21, 2018 1:00 pm

Since I work with aluminum most of the time, I ponder the use of different aluminum alloys. If I want strength, I go with a 7xxx series like 7075; for less strength, but good formability, I go with a 2xxx series, like 2024 and for average quality (strength/machinability), I go with 6061. That's about all the alloys I use, but I was wondering about 2024 alloy as I understand it work hardens. Will work hardening occur on a piece that is being machined? 2024 also known as duralumin was used for the skin of aircraft like the DC-3 and performed well over the years. Some DC-3's are still flying somewhere in the world. Would work hardening cause the material to eventually fail due to brittleness?
Mr.Ron from South Mississippi

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GlennW
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Re: Metalllurgy question

Post by GlennW » Fri Sep 21, 2018 3:43 pm

I'm not sure that it work hardens like some steel or bronze alloys do when machined, but it does have a fatigue life.
Glenn

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Mr Ron
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Re: Metalllurgy question

Post by Mr Ron » Fri Sep 21, 2018 6:27 pm

I guess I worded this wrong. I wanted to know if the type of machining would induce work hardening. For example; would milling a slot cause it to work harden?
Mr.Ron from South Mississippi

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tornitore45
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Re: Metalllurgy question

Post by tornitore45 » Fri Sep 21, 2018 6:31 pm

Never noticed a problem machining 2024, I use it for con-rods and heads and machines much nicer than 6061.
Mauro Gaetano
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KellyJones
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Re: Metalllurgy question

Post by KellyJones » Sat Sep 22, 2018 9:29 am

2024 (and other aluminum alloys) are precipitation hardening. That means given temperature an time, alloying elements will migrate within the metal and form tiny clumps, which strengthen the alloy. Some alloys do this at room temperature. The upshot is, that unlike some CRES alloys, aluminum alloys don’t apreciably work harden. You should be able to machine without fear. ( of course, don’t overheat it) :D
Kelly Jones, PE
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John Hasler
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Re: Metalllurgy question

Post by John Hasler » Sat Sep 22, 2018 10:21 am

Kelly Jones writes:
2024 (and other aluminum alloys) are precipitation hardening. That means given temperature an time,
alloying elements will migrate within the metal and form tiny clumps, which strengthen the alloy.
Some alloys do this at room temperature.

I recall reading of a vendor who shipped aluminum alloy rivets packed in dry ice. They were dead soft until they had been at room temperature for a few hours.

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GlennW
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Re: Metalllurgy question

Post by GlennW » Sat Sep 22, 2018 11:11 am

Those were DD rivets. (2024)
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tornitore45
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Re: Metalllurgy question

Post by tornitore45 » Sat Sep 22, 2018 1:17 pm

I recall reading of a vendor who shipped aluminum alloy rivets packed in dry ice. They were dead soft until they had been at room temperature for a few hours.
But. but, but were they kept in dry ice since the bar was extruded and through the forming process?
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GlennW
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Re: Metalllurgy question

Post by GlennW » Sat Sep 22, 2018 2:06 pm

No, they were kept on dry ice after they were quenched.

I've seen small table top furnaces about the size of a beer mug that are used to re-heat treat the rivets just prior to use.

The manufacturer will also do that for you and then ship them via air freight packed in dry ice.
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Harold_V
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Re: Metalllurgy question

Post by Harold_V » Sat Sep 22, 2018 6:00 pm

GlennW wrote:
Sat Sep 22, 2018 2:06 pm
No, they were kept on dry ice after they were quenched.

I've seen small table top furnaces about the size of a beer mug that are used to re-heat treat the rivets just prior to use.

The manufacturer will also do that for you and then ship them via air freight packed in dry ice.
Yep, what Glenn said. In order for aluminum to age harden, it must first be solution annealed, which is a process by which the items in question are heated to the proper temperature (very near the melting point for aluminum), then quickly quenched. Quenching "locks", for lack of a better description, in an evenly distributed state, the portion which is precipitated . The process of aging begins immediately, and is lengthened by super cooling. The process can be repeated by another solution anneal, which causes the precipitated constituents to, once again, be evenly distributed in the material.

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