Porosity in 6061 aluminum

By Lawrence (*****)

Date 08-20-2010 22:16

Hey Ringo!

Couple things come to mind right away...

Back off the balence control 5 percent and continue to back off in 5% increments until you get good etch and wetting at the toes. Remember that the balence control on your Dynasty when set to 70 is several percentage points of EN beyond what a synchrowave will put out when set to 10 (max penetration)

Also if you can't avoid the bead blasting, prior to the blast operation, at least mask off the area to be welded to a minumum of 1/4 inch beyond the projected weld toes and be sure to sequence the carbide burr operation *after* the bead blast operation.. The oxide in the blast media can be problematic.

Set AC frequency to about 220 to help increase your chances of getting good fusion in that "U" groove

BTW Sweet lookin fixture.

By 803056

Date 08-23-2010 14:39 Edited 08-23-2010 14:42

6061 aluminum is time at temperature sensitive. The heat treatment being used will degrade the mechanical properties. I would question whether the procedure was ever qualified and met the minimum tensile strength requirements with the conditions stated.

Grit blasting with aluminum oxide? Isn’t that what you are trying to remove before welding? Aluminum - melting point - 1200 degrees (roughly), aluminum oxide - melting point - 3200 to 3600 degrees. Hmmm!

You stated the material is "wiped" with acetone. Try this: wipe a clean piece of polished aluminum with acetone and wipe a second piece with isopropyl alcohol (90%). Which cleans clear and which leaves a residue?

Wiping with a cotton rag or paper towel will leave some lint behind. The lint is cellulose that decomposes in the presence of the arc and introduces hydrogen into the weld puddle.

Is the porosity shiny silver in color? Look for a hydrogen source: lint, fingerprints, feeding filler rod into the weld puddle without wearing gloves, etc.

Try this; look at your thumbnail. The surface of the thumbnail is typically somewhat dull. Rub the thumbnail against your nose and look at the thumbnail. It will be a shiny gloss from the oils in your skin. The same oils are present in your skin to keep it soft and flexible. That oil is a great source of hydrogen.

If the porosity is discolored when broken open, your problem may be linked to insufficient shielding gas coverage.

After looking at your photomacrograph, I would hang my hat on hydrogen.

Best regards - Al

By Ringo

Date 08-23-2010 21:14

Right on Al,You and Lawrence have given us some good advice.I bet we'll slick 'em in now.

By Ringo

Date 08-23-2010 21:11

Thanks a lot Lawrence,I'll give it a shot.I'll let you know.

By 357max

Date 08-24-2010 01:09

The syncrowaves max out at 68% negative the lincolns squarewave maxs at 65%. So 70% shouldnt cause the porosity.

By Lawrence (*****)

Date 08-24-2010 06:09

I dunno about that Max.

Under perfect prep conditions maybe your right.

But I've seen plenty of issues with lack of etch or lack of cleaning action with balence set below 70%.. Usually due to lack of oxide removal or some other contaminant that just could not be fully etched with the minimal DCEP of those settings.

That higher EN dwell time along with the known oxides left from the bead blast and I can see porosity and lack of fusion at the toes being the result.

Am looking forward to hearing from Ringo on what happens next.

By Ringo

Date 09-30-2010 19:54

Still having porosity issues.We have followed all the advice,and tried a 250F preheat.I have never seen porosity come up like this in 6061 before.It usually welds great.I'm going to try to weld a sample tomorrow,and see what happens.Anymore help would be greatly appreciated.

I'll try to post some pics soon.

By Milton Gravitt (***)

Date 09-30-2010 20:05

Ringo this part looks like it was machined if it has it could be the coolant causing the porosity issues. Don't know if this will help but we have had troubles like that and it was the coolant that was used while it was being machined.

M.G.

By Ringo

Date 09-30-2010 20:15

That's a good point,but I figured the 250F preheat would have vaporized any remaining coolant.I guess I could look up the MSDS and see what point it turns to gas.

By ssbn727 (*****)

Date 09-30-2010 20:30

Just out of curiosity Ringo... Was one of the parts grit blasted with some sort of medium like fine glass beads or some other fine blasting medium? Some of it, or any of the remaining coolant on the surface of the part may have been impregnated into the surface and is causing the porosity due to it coalescing with the weld pool. I may just be barking up the wrong tree, but it cannot hurt to ask at this point. ;)

Respectfully,
Henry

By Ringo

Date 10-01-2010 10:36

We did change the blast media from aluminum oxide to glass bead.Some of the samples we just prepped with a carbide burr,still the same result.

By 803056

Date 10-01-2010 14:21

Are your welders cleaning the filler metal?

If so, what are they using and how are they cleaning it?

Are they wearing gloves when they handle the filler metal?

Porosity in aluminum is usually associated with hydrogen. Sources of hydrogen are many, not to be forgotten are the oils in the skin which are easily transferred to the filler metal if "clean" gloves are not worn. Wire brushes, tools, and stainless steel wool should be cleaned before every use. Even the gloves being worn are a consideration. "TIG" gloves are made using a process that does not use any oils to make the leather soft. Regular leather work gloves will not do if the quality requirements are on the high end of the quality spectrum.

The source of your problem can even be the base metals supplied to the welders. Castings are welded on a regular basis. If the castings have porosity, the welds will as well. The quality can be no better than the raw materials you start with.

Cutting fluids used with band saws, drilling equipment, etc. will not be removed with alcohol alone. Cleaning may require a couple of steps; remove heavy oils with a suitable solvent, followed by a wipe down with acetone, finally sprayed with 90% isopropyl alcohol to remove the last bit of residue.

Welders/material handlers often do not appreciate the need to keep base metals clean. They handle the cleaned raw material with their bare hands or grimey work gloves, lay the cleaned material it on surfaces that are contaminated with only God knows what, the list could go on for several pages. That simply will not do it porosity free welds are required.

Why are you grit blasting? The media used will embed into the softer aluminum base metal. Even power brushing will burnish the aluminum and embed oxide into the aluminum.

Are you draw filing the joins before welding them, and if you are, are the tools cleaned before use to remove contamination and oils? Are your wire brushes cleaned with isopropyl alcohol before each use? Is the wire brushing done using a back and forth motion or in one direction (like using a hacksaw, which is the better way)?

Looking at the photograph of the section through the weld, I would look at the cleaning methods, storage, and handling, as well as general house keeping practices in the shop.

Good luck - Al

By Ringo

Date 10-01-2010 15:45

The weld wire is wiped with acetone with a clean shop rag.I haven't been back there the whole time they are welding,so I'm sure if they are handing the weld wire with their bare hands.There has been no draw filing,just carbide burrs.we changed the blast media from aluminum oxide.

I welded one for engineering a few minutes ago.And I used new tig gloves,new tungsten ground with a tungsten grinder.Also,I wiped the filler metal down with acetone,and never touched it with my bare hands.Everything welded great.I let you know after it's cross-sectioned.

By Milton Gravitt (***)

Date 10-01-2010 18:14

Ringo, I would like to see the cross section if you don't mine posting it. you have my curiosity going now and it might help some down the road.

M.G.

By Ringo

Date 10-01-2010 19:35

You can take a look at the first post.That was one of our welders first attempt.

By Milton Gravitt (***)

Date 10-02-2010 00:25

I meant the one you where going to do yourself. I have looked at the other cross section and seen all the porosity in it.

M.G.

By ssbn727 (*****)

Date 10-01-2010 18:59

Hi Ringo!

I have got to agree with Al regarding the cleanliness factor that must be incorporated as part of the assembly/welding process... With Aluminum as well as other sensitive metals like Titanium which is reactive, hydrocarbons of any origin are not "weldcome" on the surface or beyond of the base or filler metals used to weld together any of these metals... They may end up breaking down to different molecules or their respective atoms, but that doesn't mean that these elements will not become entrapped within the weld pool either. ;)

So as Al mentioned earlier, Cleanliness is Godliness! ;) I also do hope that you'll consider what Al mentioned regarding the grit blasting as well.

Respectfully,
Henry

By Ringo

Date 10-01-2010 19:49

Oh I agree with Al too Henry.I finally welded one to see why everybody was having so much trouble.And I had two spots of porosity that were out of limits.I kept everything as clean as possible,and still the porosity.I used to think I was a pretty slick welder,but this has been very humbling.I'm going to step up the size of the tungsten to 3/32" from 1/16",because at 145 amps is a bit much for 1/16,as it starts to split at the point at that amperage.

By Tommyjoking (****)

Date 10-02-2010 16:43

I totally agree about all the cleaning and prep....that is always the first place I look with porosity in AL.

Ringo is the beveling done before or after the blasting? I ask because it is so common to use wax on those carbide burrs to keep them from loading up. Al has a lot of good points but the grit blasting may be the major issue, I have run into that before with parts "cleaned" that way. Right before welding you might try a fresh SS toothbrush in that groove (and on all the edges where your arc will go), brushing in one direction only till you "shine it up", then a little blast of compressed air to remove stray particles. I know that sounds odd but it has helped me with similar problems to this. I think it gets rid of blasting material stuck in the surface. I basically got to the point I would NEVER weld a grit blasted surface until I shined it back up. I also agree with the tungsten change, that is a pretty thick fixture.

By 803056

Date 10-03-2010 04:05

Watch the compressed air. Compressors use oil as a lubricant.

Al

By Ringo

Date 10-04-2010 10:36

He have oil separators in place,but I don't know if they catch it all.

By Ringo

Date 10-04-2010 10:35

The beveling is done before the grit blast.

By Lawrence (*****)

Date 10-04-2010 12:41

Ringo

The sequence of processing is something I touched on the first post.

I think if you can't avoid the bead blast totally, because of epoxy paint removal or something similar, it should at least be scheduled before the machining/bevel operation.

This way you can machine away any impacted blast media. Also you will need a cleaning step after your machining operation to remove cutting fluid etc. Vapor degrease is best but most folks don't have access to that these days.

Another possibility that crosses my mind is simply hydrogen bubbles left in the puddle because of an overheat condition at the weld. That fabulous fixture can only drink away so much heat eh? If the operator is slow in depositing the weld or doing multiple fill passes without time for the temp of the base metal to drop you can get porosity in a perfectly prepped componant. Usually (not always) you will see a slightly grainy appearence on the weld face for this condition. Take a little time between passes... Your gonna have to put your foot into it to get the sidewalls to melt but you really need to get in and get out.. Hot and fast with some time between layers.

By Ringo

Date 10-04-2010 14:18

Sounds like a good idea to me.We do have access to vapor degrease cleaning.

By Ringo

Date 10-29-2010 23:57

We finally got that repair all squared away.I appreciate everybody's advice (Lawrence,Al,Henry,et.al).We eliminated all sources of hydrogen,and adjusted the parameters on the Dynasty,and Bingo,the porosity went away.Rolls-Royce was happy.

Thanks,Ringo

By Lawrence (*****)

Date 10-30-2010 01:06

Well Ringo

Tell us about the parameters!

Way to go!

By Ringo

Date 10-31-2010 05:04

I'll have to wait till Monday to see what we actually stored on that Dynasty.It's late Saturday night,and I've had several cold ones after watching my poor Vols get smoked again.You've always been a good source of info,and I applaude you for it.

Later,Ringo

By Ringo

Date 11-04-2010 12:19

The Ac frequency was set to 230,and A/C balance was set to 60% positive.I went up to 3/32 tungsten,but the results weren't as good,so I went back to 1/16.