Aluminum TIG question

[churchjw]

I welded some aluminum parts last night and after welding I machined the part back down and the surface finish was horrible. Before welding I got great surface finish on the lathe. Tooling was HSS and rpms around 400. The setup was the same only the part was longer. But the machining is only right at the chuck and the other end is held with a center in the tail stock. So I don't think is was vibration in the lathe. It looks to me like the metal ripped rather than cut. Is it just the fact that the aluminum was annealed when welded? Or did I do something wrong and how do I keep from doing this in the future?

The settings:
AC TIG on a lincoln 225
Argon shield gas
170 amps
AC balance set at auto
Base metal is 6061
Filler rod 4540 (I am fairly sure it could be 4045 couldn't remember this morning)
The base metal was preheated with map plumbers torch



Here is a link to more pictures of the project.
http://www.flickr.com/photos/24370911@N08/sets/72157634667895309/

My hat is off to you guys that pipe weld all the time. Man its hard to do and keep the part straight.

Jeff

 

[Ray C]

4043 is the typical filler rod and I've machined-over it many times.

Question: How long after welding did you do the machining?

The part has to fully cool to natural room temperature. Working on really hot aluminum or, aluminum which has very recently been welded will cause problems but admittedly, I've never seen it that bad. Still though, I think the weld was too fresh and did not "cure" yet.


Ray

 

[churchjw]

4043 is the typical filler rod and I've machined-over it many times.

Question: How long after welding did you do the machining?

The part has to fully cool to natural room temperature. Working on really hot aluminum or, aluminum which has very recently been welded will cause problems but admittedly, I've never seen it that bad. Still though, I think the weld was too fresh and did not "cure" yet.


Ray

I think that is the problem. I water cooled the parts then put them on the lathe. Less than a minute between welding and machining. So for future reference let that parts air cool then machine. How long is a good idea to wait?

Jeff

 

[Ray C]

Oh yes, I'd say that's the issue for sure then. I wish I had a precise answer about the "curing" time -but I don't. I will take a guess and say it's at least 2-3 hours and possibly as much as 24. This is a purely uneducated guess on my part based on a few small things I know about how aluminum is tempered. It just so happens that when I encounter these situations, I tend to do the work over several days and rarely ever does a part go from weld into a machine on the same day.


If I weren't in the office right now, I'd look it up. Perhaps you can do some research too...


Ray

I think that is the problem. I water cooled the parts then put them on the lathe. Less than a minute between welding and machining. So for future reference let that parts air cool then machine. How long is a good idea to wait?

Jeff

 

[Grumpy Gator]

I didn't see any mention of cutting lube when you made your cut. Al can be real sticky to machine.
I have used WD-40 or wax and gotten good results.
Also start with a lite cut till you get past all the hills and valleys. Al does not like an interupted {Hit and Miss} cut as it will want grab and tear.
I water cool DOM tube all the time. If I weld cast I just set it in front of a fan till I can pick it up barehanded.
Hope this helps.
***********Just Saying*******************G**********uch:

 

[sniggler]

How did the weld look? Also 6061 retain only about 20% of its original strength in weld zone the heat effected zone with be soft and won't be very forgiving when machined. 5053 as a filler metal is a little harder. If the weld went in well the part should still polish up ok with some possible color variation at the weld. As for post weld pre-machining heat treatment the info is out there.

The post weld strength needs to be considered against the final application.


Bob

 

[Ray C]

FWIW... I do a fair amount of TIG aluminum welding of "structural" pieces and not as much for pieces that will be machined later on. Most of it is 6061-T651. Immediately after a joint weld both the weld and heat affected zone are very soft for about 15 minutes after the weld. About an hour later, the weld becomes very hard and the surrounding area hardens-up just a bit. After several days to a week, the surrounding area also hardens and returns to about its same condition prior to welding. This is hardly scientific but, I've seen this dozens of times.

I also machine a good bit of non-welded aluminum. Once you make a fresh cut, it looks beautiful but, is very fragile and will scratch just by handling it or rubbing with a soft cloth. Within hours, the surface almost seems to get very slight wrinkle marks. This is the beginning of the aluminum aging/oxidizing process. After several days to weeks, it eventually gets a gray dull finish and returns to a much harder state.

There are several types of treatments for aluminum and it's specified by the last digits. In the example above the T651 means Tempered and stretch relieved. Although I don't do this to the things I make, tempering is done by heating to about 80% of it's melting temperature then slow cooled followed by heating to 50% the melting temperature, holding for 24 hours, followed by a quench.

The point is, if you need to weld and machine a piece, there's a few heat treating/tempering steps that should be done. On the stuff I've welded and machined, it was mostly "cosmetic" parts and I've had good luck with welding, waiting for it to cool completely then machining. Purely by chance, it's usually a day or so after welding that I get around to machining.

In the matter of steel, I regularly do welding and machining and this is one of the reasons I setup a heat treating oven as, there are techniques and procedures to follow -beyond the scope of this thread. So far though, I've have very good success working on welded steel ranging from low carbon to high carbon as well as 4140 and 4145.

EDIT: Most stainless steels are not finicky about welding and machining. Weld it, let it cool completely (w/o a quench) and machine it. I do this fairly regularly on 316.


Ray

 

[Tom Griffin]

The heat from welding annealed the 6061 so it will never machine like it did before welding. You can use different alloys of filler to help with anodizing, but the only way to improve machinability would be to re-heat treat the part after welding. Grumpygator's suggestion of using WD-40 is a good one. I've repaired a lot of motorcycle heads and that's what I used to improve the machinability of the welds in cast aluminum. It seriously does machine about as good as chewing gum, but the WD-40 at least makes it doable.

Tom

 

[TOOLMASTER]

yeah that happens..
been there done that

 

[churchjw]

Thanks guys this was just what I was looking for. I did some reading last night and found lots on hardening Al. Looks like in basic that you have to heat the part to a set temperature and hold it there for a long time, 8 hours plus. From the reading it looks like it lost about 80% of its hardness when I welded it in the heat zone. The part polished up fine so its just a matter of it not breaking. The wall at that point is double thick anyway because I was afraid of burning through. This is going to be used to hit people (sparing not in anger) so it needs to take some force. The original handle has a wall thickness of around .050" and the new extensions I made are around .125" wall thickness and double that at the weld. So would you guess I am worried about nothing?


So my question now is how do you guys handle heat treatment in a hobby shop or do you? This part is 5 feet long so no way its going in an oven. For smaller parts I could get a toaster oven or something like that, but the electricity usage for 8 or more hours not to mention the fire risk has me a little worried. Do most hobbyist skip this step and just over build the original part or use Ray's method and wait for the part to harden on its own? Ray's method looks to be the only one I could do in my shop.

This has been so helpful thanks to everyone. I want to start trying anodizing and I had no idea 4045 rod would cause problems. I will pick up some 5053 rods to try next.

Jeff