Heat treat of 2014/2219/355 welded assy

[rayhawk]

I have a 355 cast aluminum housing that has been previously welded and heat treated. I am looking for a postweld heat treatment after welding a new piece of 2219-t3 plate and 2014-t6 bar stock to the housing(2219 plate directly to the housing, then the 2014 piece to the 2219 plate). I plan on using 2319 filler rod. I understand that I will be overaging material that has previously been aged, that is the casting and other wrought sections already welded to it. What would be a good compromise for postweld heat treat time and temperature? My goal is to maximize strength in the HAZ, and I was going to start with 4-6 hours at 325F. Obviously this will not produce a T8 hardness in all the components but I have to compromise in some way here, so I think this should give me something acceptable. Any input would be appreciated.

 

[Matlsguy]

Hello Rayhawk,

How about fully solutioning the assembly after you weld the new parts into it? Then age it as an assembly.

Regards,

matlsguy

 

[rayhawk]

This is a step I would rather avoid due to the complexity and many finished machined surfaces of the part and I dont want to cause warpage anywhere I can avoid it.

 

[Matlsguy]

Rayhawk,

I just checked my ASM Heat Treating Handbook. I need to make a few points. 325F (162C) is too low a temperature to stress relieve the fixture after welding. That temperature is the optimal aging temperature for these alloys. To stress relieve, you need a greater amount of diffusion; thus the temperature needs to be higher. ASM reccomends 500F-800F.
Next point, since you are heat treating A355 (high thermal conductivity and thus low thermal stresses) warpage shouldn't be a problem if a reasonably low temperature ramp up and ramp down rate is used.
Last point, is you heat treat in a argon atmosphere the machined surfaces should't be ruined. Surface finish shouldn't be an issue since you are going to have to heat treat above 500F anyways for stress relieve
I think you can still get a T8 hardness. Good Luck!

Matlsguy

 

[rayhawk]

Thanks for all the help. I was looking in the ASM handbook for welding, brazing and soldering, and found some good information. It talks about welding parts in a T4 condition and then aging after welding. Of course this does not exactly apply because I have an already aged housing that I am welding to. It does not give exact specs for my scenario but I figure it should be a good starting point. To get maximum strength you are right that the only way is to re-solution heat treat after welding. I am not currently set up with quenching capabilities for this size part, but if I have to I will figure out how to do it. Thanks again.

 

[Matlsguy]

rayhawk,

I would think you need to stress relieve after welding the assembly prior to aging. For the solutionizing process, you might need a fixture to prevent any distortion if you plan on oil quenching. To quench this material you don't need the high quench rates such as that to form martensite as with steels. You might be able to get away with backfilling the furnace with argon at a high turnover rate. Distortion will be minimal using this quenching method. I would recommend stress relieving, then solutioning, then aging.

Matlsguy

 

[swall]

If you end up solution treating the weldment, you will not want to go above the 935F solution treatment for 2014, otherwise you run the risk of eutectic melting. This temperature, unfortunately will be too low to properly solution treat the 2219. But you already appreciate that you will not get optimum properties with this project. How did you come to decide on 2219 filler rod?

 

[swall]

That would be 2319 rod!

 

[rayhawk]

It seemed to be the best choice per the ASM handbook.

 

[swall]

For the welds to the 355 casting you would have the option of using 4043 rod.

 

[Matlsguy]

Swall brings up a good point. Why use a high alloy filler rod like 2319? I understand that you want your weld material to have comparable properties to the parent metal, but high Cu and low Si wouldn't be my first choice because the high Cu/low Si creates other problems such as hot cracking issues. Do the welds get inspected via FPI or X-ray? I would go with the 4043 filler because its of its shorter freezing range and higher fluidity. It doens't have the same hardenability as the other parent metal or the 2319, but it does have better weldability. No matter what you do your weld metal will never have matching properties to your parent metal. What I have suggested is solution heat treating to counter act HAZ overaging.

matlsguy