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Up Topic Welding Industry / Technical Discussions / OK, LET`S HEAR IT PROBLEMS WITH ALUMINUM
- - By LAMAN Date 12-22-2002 14:01
WE`RE HAVING TROUBLE WITH POROSITY AND TUNGSTEN INCLUTIONS[6061 BASE METAL-4043 FILLER WIRE,GTAW 100% TUNGSTEN,AC, HI-FRIQ,WATER COOLED,ARGON,ACITONE CLEANING,FLAPPERWEEL BUFFED,PREHEATED,6" SCH. 80, J-BEVELS. WHAT ELSE CAN WE DO TO HELP OR FIX THE PROBLEMS WERE HAVING? THE WELDERS I`M TESTING HAVE OVER 20 YEARS RT QUALITY PIPE WELDING EXP,SO I DON`T THINK THERE`S A PROBLEM BETWEEN THE SHOULDER AND THE HOLDER.PART OF THE PROBLEM IS WE DON`T DO MUCH ALUMINUM WELDING [PETRO-CHEM MAINT.].WE DON`T HAVE MUCH TIME,I HAVE TO REQUALIFY THEM SOON!!! ANY INLIGHTENMENT ON THIS SUBJECT WOULD BE APPRECIATED,TIP`S,AND NEW PROCEDURES,THANK YOU AND MERRY CHRISTMAS
Parent - By Niekie3 (***) Date 12-22-2002 15:24
In Al, porosity is generally caused by hydrogen. You need to eliminate all sources of moisture or hydrocarbons.

Have a look at your oxide removal again. It must be clean because the oxide attracts water out of the atmosphere. In addition, you must be carefull with the acetone. Some acetones have oils in that can leave a residue when you use it to clean with.

The Tungsten inclusions are basically a problem with welder technique. They must not scratch-start or in any other way touch the base metal with the tungsten.

Hope this helps.

Regards
Niekie Jooste
Parent - By Michael Sherman (***) Date 12-24-2002 12:23
To elaborate on the above post and to add the your cleaning process that is already in place: Clean the inside of the pipe atleast one inch back from the weld. Use stainless steel wire brushes immediately preceding any welding, everytime you stop, before welding again use the stainless brush. Running too cool (low amperage) will also cause porosity by allowing premature solidification of the weld metal. The tungsten inclusions can be caused by using too small of a tungsten. Aluminum sch. 80 pipe needs at least 1/8" or 5/32". If the tungsten is dipped, welding must stop immediately and the weld and the tungsten must be ground. Use a gas post flow if possible, check your flow meter (35-40 cfh). Check your cup size too. Porosity is caused by gas trying to escape the molten puddle, eliminate the source of the gas, keep the puddle molten long enough to let any remaining gas escape and you should eliminate your problem. One last note, check your equipment too, a leak or bad connection somewhere in the gas or water lines will give you fits.

Mike Sherman
Parent - By mcwelding (**) Date 12-24-2002 18:45
hey laman,
one prob i had was the back screw in piece of the tig torch had a crack. another problem is acetone. it is a poor degreaser and leaves residue. if the alum has a somewhat clean appearance use regular iso. alcohol. it is safe, degreases, evaporates. make sure it evaporates before you weld. also wipe down the filler metal with alcohol and any other thing yer clean lookin but naturally oily fingers touch. clean gloves. and make sure not to add filler until you have a nice shiny molten puddle. if you dont have a nice shiny clean puddle, yer already lookin for probs. what are you using to preheat? torches create h20. porosity is a direct result of hydrogen, like mentioned above. hey, im not tryin to act like a pro but i attended an alcotec alum seminar and discovered alot of bad alum habits. check out their site. www.alcotec.com since i went to this seminar, i havent had one bad time with alum. dont use a hard wheel on the grinder, it will smear grit into base, use stainless brush or wheel and soft abrasive disk, keep rpms low. you must removed the aluminum oxide. do not let the tungsten touch the alum at all. good luck
rich
Parent - By brande (***) Date 12-28-2002 08:00
Seems as if you have most of your stuff covered.

A couple of things come to mind that might help.

First-make sure you degrease with acetone or other similar solvent. Acetone does not cut all greases and oils. Toulene or MEK can sometimes remove what acetone can't. Be sure joint is dry before assembly.

The other thing-use no abrasive products prior to welding, whether they are rated for aluminum or not. Abrasive products (grinding wheels, sanding discs, flap wheels, etc) tend to leave grains of abrasive in the soft aluminum. When the welding arc hits these grains, they steam or volitize in the weld puddle easily and can cause porosity. The same goes for sandblasting. Yes- sandblast media including glass bead can lodge under the surface and cause porosity.

Degrease first-this is important-then prep the weld with a carbide burr or similar cutter. Prepping before degreasing will drive contaminants deeper into the base metal. Be careful if you prep on a lathe, mill, or similar machine. A lot of oils used on these machines will not come out with solvent. Aluminum likes to absorb oils and greases.Trying to "burn" these contaminants out with a torch will evaporate the solvents or carriers, but will leave the solids behind-not a good thing.

One last thing-be sure you penetrate the weld completely before adding filler metal.
You should see a clean shiny puddle at the bottom of the groove before adding filler. If you are too quick adding filler on aluminum, you will trap the root joint groove. This can lead to incomplete fusion problems or if the groove is contaminated, porosity.
If you can-be sure to "work" the weld so that any porosity can boil out to the surface.

If the J-groove is not dictated by code or print-a joint known as an "extended land bevel" can really help. It is very common in code aluminum pipe welding. Email me for details.

Let us know how you make out!!

brande
Parent - By chall (***) Date 01-06-2003 15:00
Excellent coverage of this topic. I'll repeat the info that we learned the hard way.

Porosity: Our experience with what you describe was cured by eliminating the use of abrasive cleaning (as stated above). If you have to do last minute cleaning only use a machining process (router bit) or stainless. We have gone to the use of 80/20 (Ar/He) gas in some cases. Truthfully though, I think we were not cleaning properly. We changed the gas and fixed our cleaning technique at the same time. I think the best step was making sure the cleaning was done properly.

Tungsten inclusion: Tungsten too small, technique unforgiving.

One last thing, experience in welding steel (no matter how good you are) does not gaurentee you will be able to do aluminum well. Charles Hall
Up Topic Welding Industry / Technical Discussions / OK, LET`S HEAR IT PROBLEMS WITH ALUMINUM

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