Alu TIG - Random small pinholes

[FASTdan]

I have noticed on occasion whilst fillet welding 3mm thick alu tube to 10mm plate that I sometimes get little pin holes appear. Usually at the extremity of the weld. Other than that the weld looks reasonably neat - not like when you have a nasty contaminated bit thats dull and rough looking.

I cant quite put my finger on what might be causing this?

Welder is a GIANT chinese machine. 2.4 white tungsten, argon shield, welding current pedal operated, but circa 180amps.

Any suggestions would be much appreciated

 

[backpurge]

Are you wire brushing all the oxide off the material before you start welding and is your filler wire oxide free as well

 

[TechnicAl]

Aluminium welds will always have some porosity, all you can do is keep it to a minimum. So the first 3 rules are
clean it
clean it
clean it again

 

[FASTdan]

I am cleaning, but perhaps that is it - never sure how rigorous to be and maybe I've gotten a bit lazy. If there's nothing more fundamental? Id best go buy a new brush!

 

[weldequip]

Correct gas would be a good start Might just be the way you've typed it, but a lot of people do refer to "Argoshield" (brand name) as Argon Shield - as you quoted; needs to be pure Argon for TIG (BOC brand name "Pureshield Argon"), not Argon/CO2 mix. It is pure Argon you are using?

 

[hotrodder]

Hydrogen is the source of porosity in aluminium, very soluble in liquid ally but not in solid Al. Hydrocarbons (oils, grease, solvent residues) are one source, water vapour/moisture is the other. Al oxide can trap any of these which'll be 'split' by the heat of the arc resulting in hydrogen being absorbed by the weldpool and then rejected as it freezes resulting in porosity

As said it's a cleanliness thing, base metal and/or filler wire. Problems with shielding quality can make it worse but will typically cause other more noticable problems too

 

[FASTdan]

Sorry yes pure argon gas.

Sounds like its definitely a cleanliness issue then.

Thanks for the responses.