What Happens to 2024 Alu When Heated and Quenched Rapidly?

[scooby2ooo]

hi!

i am trying to find out information on what happens to 2024 alu when it is heated and then quenched rapidly. i am trying to find information relating to grain boundary segregation as the rate of cooling is changed. does anybody have the knowledge of a good source?

thanks guys

 

[Gokul43201]

Have you tried any of these:

1. Aluminum Standards and Data, The Aluminum Association, Inc., (1982)

2. Properties and Selection: Nonferrous Alloys and Pure Metals, Metals Handbook, ninth edition, ASM International, Metals Park, OH, volume 2., (1979)

3. Heat Treating, Metals Handbook, ninth edition, ASM International, Metals Park, OH, volume 4, (1981).

4. L.E.Brandes, Smithells Metals Reference Handbook, 6th edition, Butterworths & Co., Ltd., London, (1983).

 

[scooby2ooo]

hi thanks for info, i have seen the 2nd and 3rd handbooks you mentioned. don't have access to the first and 4th.

what i am interested in is for 2024, what happens to the copper when it is heated then cooled. its in relation to welding and the HAZ. the segregation at the grain boundary

i am trying to replciate the effects with a heat and quench experiment, showing what happens in different areas of the HAZ when the metal is welded.

i think I am struggling to understand the background information which is why i am finding it difficult to search for the information!

do you know how i can fidn good info illustrating grain boundary segregation with respect to heating and cooling.

thanks

 

[scooby2ooo]

am i correct in thinking that intergranular corrosion is the problem i am investigating?

 

[Gokul43201]

Look up this paper:

B. C Meyer et al, "Dispersoid-Free Zones in the Heat-Affected Zone of Aluminum Alloy Welds", Metallurgical and Materials Transactions A, Volume 31, Number 5, pp 1453-1459 (May 2000)

The context of this project is a little unclear - is this a predetermined topic? How can you be given a project topic and still not know what it is you are investigating? Shouldn't that be specified in the description? It is very possible that you are required to investigate the resulting loss of intergranular corrosion resistance (due to the dissolution of Cu near grain boundaries, and related effects I can't recall), but it's not something we can tell you.

To my knowledge nobody welds a heat-treatable aluminum alloy (2024 may be an exception, I don't know) because of a significant loss in mechanical strength (heck, even non-heat treatable alloys are a pain to weld, but they don't behave that poorly afterwards).

You need to be aware of the typical heat treatment process (precipitation hardening) for an Al-xCu alloy (x < 4%). In addition, you might need to be aware of ttt curves for these alloys; the peak temperatures and cooling rates in different parts of the HAZ can vary by a lot.

Before you embark upon the project, make sure you:
1. have defined the scope of the project completely. What is the objective of your investigation?
2. have charted out in detail the various techniques you wish to employ (specific heat treatment, types of microscopy, choices of mechanical testing, etc.)
3. have acquired the necessary background knowledge from a literature survey and textbook study.

 

[scooby2ooo]

you seem to have hit the nail on the head in your post!

its a predetermined project yes, i was looking into pfz's but as this isn't in the brief i have to avoid it.

as i understand it, it is to do with a new form of CO2 cooled welding, but that won't be taken into account when doing the experiment etc. i will explain:

the essential idea if to model what happens in the HAZ when the 2024 is butt joint welded.

my part is to replicate the heating up (from the weld torch) and cooling of the HAZ as the torch passes over the join.

the experimental side is to heat up a sample , to a temp as to make sure any treatment carried out are taken out of the material. then to quench the samples in different mediums.

water. air, CO2 and oil.

as i understand it the different cooling rates will replicate the distance away from the join in the HAZ.

the main problem i have is actually understand the possible effects at the grain boundary when this heating and cooling is taking place.

the description mentions investigating inter granular corrosion , grain boundary segregation and and inter granular cracking. that's fine but i need to understand the background to these problems before i try and determine what is going on in my material!

i will be using a field emission gun TEM (well i won't be operating it just supplying the samples to investigate)

where i am having trouble is relating all these processes, i have journals and books but i need to find a source of good background info that will enable me to decifer the information from jounrals better.

the peak temps and cooling rates in the HAZ as you mentioned is (from what i understand) is what i am looking to investigate.

i think the loss of intergranular corrosion resistance is what i am looking for, but i need to understand the whole concept first: that is the problem

thankyou for your help

 

[Gokul43201]

I'm so out of touch with this stuff, I can't hardly recall the texts I used. The right person to help here is Astronuc!

Astro: can you recommend any books where the OP can learn about the physical metallurgy of the heat treatable aluminum alloys - specifically with respect to grain boundary segregation and effects on intergranular corrosion resistance?

I can't remember what books I used for non-ferrous physical metallurgy. As for the corrosion aspect, I'd hesitantly (because I can't recall the content of it any longer) suggest Fontana.

 

[Astronuc]

I'm so out of touch with this stuff, I can't hardly recall the texts I used. The right person to help here is Astronuc!

I was going to recommend Gokul.

Astro: can you recommend any books where the OP can learn about the physical metallurgy of the heat treatable aluminum alloys - specifically with respect to grain boundary segregation and effects on intergranular corrosion resistance?

I can't remember what books I used for non-ferrous physical metallurgy. As for the corrosion aspect, I'd hesitantly (because I can't recall the content of it any longer) suggest Fontana.

The references cited are good, and Fontana and Greene is the classic, however I think it falls short on the details of specific alloys.

I'll look through what I have, which includes several ASM Handbooks.

2024 is a very common alloy, especially for aircraft frames.

Perhaps the best people to ask are Alcoa or Alcan. I would expect they have technical reports on the welding of 2024 or HAZ and intergranular stress corrosion cracking.

http://www.alcoa.com/global/en/products/product.asp?prod_id=1695&Product=&Business=&Region=&Category=&Query=2024&page=0

Alcoa Alloy 2024, a cold finished aluminum wrought product, provides high to moderate strength, very good machinability and weldability with improved stress corrosion cracking resistance.

What thermal treatment of 2024?

 

[scooby2ooo]

hi,

i have the asm handbooks volumes 2,7 and one other, welding and brazing one i think.

i also have fontana, it has a bit on intergranular corrosion, but very little!

i need to find out what causes it, especially in 2024 with the copper

also i want to know what happens to the copper when its heated and quenched. i am expectign some form of degredation.

are you asking me what the heat treatment is of my 2024?

which for the experiment will be none. it will be heated before to remove and heat treatments rpeviously carried out.

the industry application of CO2 cooling is a big part of the experiment, seeing what happens when it is heated then quenched by CO2.

thanks for the help

 

[Astronuc]

I responded by PM, but here is some of the information I provided for those interested.

Here is a good comment on intergranular corrosion -
http://www.corrosion-doctors.org/Forms/intergranular.htm

Here is a good comment on exfoliation corrosion -
http://www.corrosion-doctors.org/Forms/exfoliation.htm

http://www.metalimprovement.com/exfoliation_corrosion.php

http://www.alu-info.dk/HTML/alulib/modul/A00121.htm

More general reference
http://www.boeing.com/commercial/aeromagazine/aero_07/corrosn.html

This is a nice reference -
http://www.engr.ku.edu/~rhale/ae510/corrosion.pdf

Corrosion essentially initiates on the grain boundaries and spreads across grains. The grain boundaries have a higher chemical (electrochemical) potential because of the mismatch of crystal lattices.

In solidification, grains nucleate more readily at phases or intermetallic of higher melting temperatures, e.g. carbides or silicides of metals. Because of the extra energy, grain boundaries are the last parts of the grains to form. During that time (milliseconds), atoms of different elements diffuse and concentrate on the grain boundaries, which is why grain boundaries can have significantly different chemical stoichiometry than the nominal composition, and it is for this reason that rapid quenching is desirable during welding or casting, otherwise subsequent heat treating is necessary.

are you asking me what the heat treatment is of my 2024?

I was wondering about the temper. See - http://www.wisoven.com/heatreat.htm (Look at comments on T4, T5 and T6)

With regard to 2024 - see http://www.auf.asn.au/scratchbuilder/metals.html#aluminium_alloys

This might be of use -
http://www.aviationmetals.net/aluminum_sheet.html

I'll have to get back later with more information on IGSCC in Al alloys.