TIG Problems "incursions"

[TheOldOne]

When I attempt to touch up a weld using TIG it seems to always look like I have introduced contaminate incursions. Just wondering if anyone else has that problem.

[chip hayden]

yes, it can happen frequently with low carbon steel and many reactive metal castings[aluminum,magnesium,etc.]. i believe what you are seeing is outgassing. i have my own solution[i'm not sure it's the best], so hopefully someone else can correct me or elaborate.

[Roger]

If your welding aluminum you have to preheat to drive off all water or you will have out gassing problems.

[Guest]

Good responce, Roger. I'm thinking he may not know that aluminum absorbs moisture. It may be dry on the outside, and still have water present. To preheat to welding temperature, blacken the aluminum weld area with acetylene, then heat it up till the black is gone, and you will be at welding temp then.
Hope this helps.

[morpheus]

To preheat to welding temperature, blacken the aluminum weld area with acetylene, then heat it up till the black is gone, and you will be at welding temp then.

Hey Rocky, is this preheating method only good for aluminum or other materials also ?

- jack

[chip hayden]

ok guys, trust me, i'm not being a wiseass, but how does the aluminum[especially in wrought form] absorb moisture? are we talking gas disassociation by arc and hydrogen entrapment or something else?
hope you don't mind wandering from the original thread but this is a very interesting subject. thanks, chip.

[morpheus]

i thought most metals, except maybe titanium or something, absorbed some degree of moisture.

- jack

[Guest]

Originally posted by morpheus


Hey Rocky, is this preheating method only good for aluminum or other materials also ?

- jack

It wouldn't hurt, but usually not necessary, except for heavy cast iron. It is normally done on the heavier materials.

[Roger]

As I understand it the moisture aluminum absorbs is in surface aluminum oxide. The aluminum surface will look and feel dry but it will have water. The water changes to hydrogen and O2 gas in arc. Molten aluminum absorbs lots of hydrogen in solution and the hydrogen has to out gas as aluminum returns to solid because hydrogen doesn't combine with aluminum. Get swiss cheese welds full of little bubbles.

[TheOldOne]

Chip

Welding carbon steel. What is your solution?

[chip hayden]

er347.
gta welds with cr and ni will hold the hydrogen in solution and not effect the weld.[when's the last time you saw outgassing in gta stainless welds?]. i also like the cb/nb [columbium/niobium] added to prevent the ouside chance of carbide precip in the heat affected zone. it also prevents machinability problems. downside is cost and ferrite number[FN]. i accept the cost because this type of weld is usually associated with small piecework-not much filler needed. finally, i've read about the fn but i haven't witnessed any loss in toughness or ductility associated with this "overalloyed" weld. try it-you"ll like it!

[Mike Sherman]

Old one, are you "dressing up a weld" made with another process, like SMAW?? Or are you dressing up a weld made with GTAW? Or have I misunderstood your question?

[Guest]

Originally posted by Roger
As I understand it the moisture aluminum absorbs is in surface aluminum oxide. The aluminum surface will look and feel dry but it will have water. The water changes to hydrogen and O2 gas in arc. Molten aluminum absorbs lots of hydrogen in solution and the hydrogen has to out gas as aluminum returns to solid because hydrogen doesn't combine with aluminum. Get swiss cheese welds full of little bubbles.

Roger, That's the simplest most understandable answer to the subject I have ever heard. Thanks!!

[bitternut]

aluminum oxide

No one has mentioned that any aluminum joint should be wire brushed with a stainless brush reserved for aluminum only prior to welding. Aluminum oxidizes very rapidly and should be brushed just before welding for best results. Just thought I would add this in case some readers may not be aware of it.

[chip hayden]

i think we are all in agreement that the hydrogen disassociates from the contaminants on the aluminum[hydrocarbons and some form of water].
i usually clean the aluminum with a basic cleaner with sodium hydroxide[like those wheel cleaners that say "NOT FOR BARE ALUMINUM WHEELS"], dry off the surface, then prep the weld area with a carbide bur. if it is heavily oxided, i have even used draino. be careful though, it fumes badly! Arcair use to make an aluminum metal prep but i haven't seen it in years.
i also wipe the cut lengths of filler with stainless wool that you can buy at marine supply houses.
i will preheat with oxyfuel if the sections are
1/2" or thicker. i also use a 95/5 ar-he blend for shielding gas. all these steps help me in getting a good weld in wrought aluminum.
now how do you guys get non-void welds in castings? especially sand cast weld repairs.