6061-T6 porosity

Date 07-22-2003 05:07

Water should never be used in the weld prep of aluminum. Water can be a source of hydrogen, a big problem on aluminum. Keep in mind that aluminum can absorb impurities and other elements easily.It is much more porous than mild steel or stainless.

Acid is an easy way to clean alum., but how do clean the acid??
Seems the cure may well be worse than the disease!!!

A method that has worked well for me, even on code jobs, is as follows-

Degrease before any mechanical preparation (carbide burr, grinding wheel, etc.). Mechanical prep can drive impurities deep into the aluminum, just waiting for the heat of the arc to bring them to the surface!

Knowing your contaminants will help with the degreasing step.
For light oils and the like, I find acetone a good degreaser. Some of the heavier oils/coolants used in CNC machining may require a slower evaporating solvent like xylol. Mineral spirits and some of these new "orange" or "citrus" cleaners don't seem to work as well, and can actually contaminate the base material. Be sure that whatever solvent used is completely dry before assembly-this is important!

After degreasing, use of a non abrasive product is essential. Bonded abrasive products (grinding wheels, sanding discs) tend to leave "grains" of abrasive embedded in the soft aluminum. These grains often volitize or burn when under a welding arc, often leading to porosity.

Sandblasting will give the same results, regardless of the media used.
Most will only sandblast aluminum once in their lifetime!!

Hope this little bit helps
Any questions-contact me directly!

Good Luck
brande

By jeffc Date 07-23-2003 02:16

Thanks for the info. These parts come off a CNC mill, of course they are using a water soluable coolant. Then the parts are sent to the finishing dept. The metal finishers are using a water and soap mixture and Alu oxide paper to finish. They than use grey pad and the soap-water mixture to finish. After the parts are cleaned in water again they are prep cleaned. As you can see there are many chances for entrapment and hydration of the oxide layer. They used to use a vibratory finisher on these parts but I convinced them that they were literly pounding water into the grain structure of the Alu. So getting back to cleaning the acid you are spot on. Why go to the trouble of etching the surface just to rinse it with water? I see I have a lot of convinceing to do.
Thanks again.
Jeff Currier

By brande

Date 07-23-2003 04:54

Jeff-as a last resort.

Find what's called a vapor-degreaser.They are expensive, and not real common-but there may be one in your area. They are basically an enclosed tank with a special solvent. This solvent is heated to a relatively high temp and the resulting vapor does the cleaning.
Much better than simply heating the parts with a torch or similar. This tends to "boil off" the liquid, but leaving the solids right where they shoudn't be.

A vapor degreaser can handle most chemical contaminants, (soap, grease, machining oils, hydrocarbons,etc).

Unfortunately, they do not remove physical contaminants (abrasive grain, sandblast or tumbler media, embedded foreign material,etc).

Hope this helps some

Let us know how you make out!!

Good Luck
brande

By ssbn727 (*****)

Date 07-23-2003 10:46

To both Jeff and brande

very good advice in using a vapor-degreaser.
However, I noticed that both of you have been concentrating on the cleaning of the base material which is good but, "does'nt cover all of the bases" so to speak.
It's just as important to also clean the the filler rods prior to welding.
If the filler rods have been out of their protective plastic seal for awhile, and have'nt been cleaned prior to welding then, the chances for the filler rod to become contaminated have increased. Surface oxides may have also formed when exposed for a prolonged period to the atmosphere, and increased humidity can also cause further contamination. Acetone or Xylol will work as you mentioned before.
Just make sure that you use a non-lint forming, non-abrasive material when you wipe the filler rods immediately before welding.

Another area that you might want to look at is the amount of moisture that can sometimes be found in the shielding gas because, the porosity may come from the increased amount of moisture in the gas cylinder or a leak in the regulator/flowmeter or conections that are'nt properly tightened. Even the gas solenoid in the machine may be a source of increased moisture in the shielding gas especially if it's location is in close proximity to the water/coolant solenoid which could transfer some of it's own condensation to the gas solenoid. this is highly unlikely but you want to "cover all of the bases". Also check the gas lines, torch connections, and if there is any type of moisture barrier between the gas, and coolant line inside the torch. condensation transfer may also be a cause here. One other possibility is that you could probably use a gas diffuser on your GTAW torch in order to shield the weld zone better.
In other words start by eliminating all of the possibilities!

To Jeff,
If you could tell me a little bit more on how thick the material is, the joint design, and the method (DCEN, DCEP, AC(HF)), and the type of tungsten you are using to GTAW the Aluminum. I then could give you some more suggestions that could help eliminate the problem you are encountering. Brande might also give you some more suggestions if there is more information provided. No offense brande!

Finally, you may want to check the amount of cfh you're using for your shielding gas, because not enough shielding gas in itself can be the cause of porosity. Even if the shielding gas is as pure as you can get, if there is enough moisture in the atmosphere then, it can easily mix itself with the shielding gas even if the flow rate is adequate or not. If you need onsite help, you may want to call your welding supplier, and ask them to help troubleshoot the problem if it still exists. If the supplier does'nt feel that they're responsible in helping you out then, get one that will!!!

A serious and complete audit regarding all aspects of the procedure being used is necessary in order to eliminate the problem. Please let me and others know what you find as the cause

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By brande

Date 07-27-2003 07:37

Porosity will rarely be caused by oxidation on the filler rod.

A quick scratch with some stainless steel wire wool should take care of any possible contamination.

Shielding gas production is rarely a cause for concern. Most cylinder gas is produced from liquid product. This will keep porosity producing (moisture) to a minimum (especially with argon).

Tungsten of the wrong type may give undesirirable opertional charateritistics, but tungsten alone will not cause poposity.

The amount of cfh is an important thing to check. Not enough and the weld can be contaminated.
Too much and the arc can be jeopardised as well as a high flow rate can actually "suck" atmospheric contamination into the weld area.
You should be using a "gas lens" equipped Linde style or Air Products/ KG style torch. These have the best gas flow.
I am sure that your answer is here somewhere.
Any other questions, please let me know.

Keep in touch and let us know how you make out!!

Good Luck-

brande