Porosity in Aluminium

[matt1978]

Have been working on a project lately which involves a lot of Mig welding of Aluminium.

It isn't really a question of IF you will get porosity when Mig welding on Ali but more a question of how much.

Hydrogen induced porosity can come from many sources, the wire, the plate itself, "dirt" of your gloves, insufficient gas, too much gas, oil and other surface contaminants and so the list goes on. It presents itself as large round holes/craters and it bad cases the macro looks like the surface of the moon.

Anyway, here you can see a couple of macro examples, one of which with gross porosity and one with minor and which is to an acceptable level. There is also a lack of penetration on the second image due to too low welding parameters.

 

[Welderpaul]

There is porosity in the top weld?

How do you prep ally before welding?

 

[matt1978]

Yes also in the top weld, you can see two small pores....but minimal and a more than acceptable level.

If your serious about it, you should look at degreasing, then grinding, then degreasing again.

As I said there will always generally be some, but of its minimal it won't be detrimental to the integrity

 

[Welderpaul]

How is an 'acceptable' level of porosity standardised?...obviously someone is not going to NDT every weld

 

[matt1978]

It will be outlaid within the welding spec. What makes it acceptable or not is to do with the size of the pores and the grouping.

Problem is with this type of Porosity it is rarely visible from the surface so visual and even dye penetrant testing isn't going to do much.

 

[Welderpaul]

We have a big ally welding job coming up soon. I've never had much luck with ally mig, so are considering tig welding it. it's going to be a long process though.

How is allowable porosity quantified in a wed spec if a visual/dye pen check won't pick it up?

 

[henry Kadzielski]

Good morning Welderpaul.
In the weld procedure and welder qualification for that procedure there were a set of parameters that have to be followed. When I did my alli qualification prior to It being submitted for testing I broke and band sawed several samples to check for both penetration and porosity which is quite visible. It is only once the welding procedure has been verified, you follow the preset conditions and all should be the same and be OK. Joint gaps, cleaning, position and welder setup (current, voltage and travel speed) are all predetermined so if they are followed there should be no problems.
If it is a bigger alli job mig it otherwise it will kill you, gas usage and fatigue
Spend the time to sort the mig out, the new machines with double pulse are great and easier. I have done all my setups with out pulse just straight mig, it is doable

 

[Richard.]

Hi Paul.
I'd GMAW your job personally as going by your usual trend of work I bet it is big?
Mig welding Alu is only difficult if there is a short cut taken in the set up which more often than not leads to a birds nest at the rollers.
Porosity acceptance. Well I'd be inclined to (if possible) push that one onto the customer.
Get a good few samples made and cut, note down the welding conditions and pass the best ones on to your customer
They accept your welding and you generate your wps to the accepted sample.

 

[matt1978]

Hi Paul,

As mentioned above, you would need to weld in accordance to a qualified WPS.

In order to get the WPS qualified you would need to pass some sort of non destructive test like X-Ray or destructive test like a Macro.

What's the details of the job? Don't forget you have Pulse and TwinPulse option on your Saprom machine

 

[Jim Davey]

You can chase your tail till the cows come home trying to make micro-porosity a thing of the past. It's always going to happen to some degree unless conditions are 100% laboratory perfect. I've seen the Lloyds acceptance criteria for a local aluminium fabricator and even they are realistic about the fact that in the real world it's virtually impossible to eliminate altogether.

 

[TechnicAl]

The first 3 rules for welding Ally.........
1. Clean it
2. Clean it
3. Clean it

and if youre not going to weld it soon clean it again before you do

dont use silicon carbide......the specialist burrs are best

buy wire from a good source and get the bagged stuff

 

[henry Kadzielski]

Good morning gents
Safra 5356 or 5183 depending on the parent material, this is what has been recommended to me to use as it has the lowest porosity when welded. In the WPS I have if you clean alli, it should be welded within 20 minutes of cleaning, otherwise as above
CLEAN IT

 

[Welderpaul]

Lads, thanks very much for your replies - sorry to hijack your post Matt.

The job isn't structural and it's non CE work, and we don't have WPS's in place for ally work as it is so rare for us to do it. It is a very large number of box section frames.

If needs be we can get a WPS sorted, but on the basis non of us can weld ally, this could be tricky at this stage

I've spent hours and hours in the past messing about trying to get our machines to weld ally and just got nowhere.

 

[TechnicAl]

The machines are the same........its the bits that make the difference..........tips, liners, torch, drive rolls

Standard MIG sets give OK results but the fancy stuff is better....pulse on pulse etc....stuff I dont understand

Im sure Matt would sort if for you

 

[didsthewelder]

hey paul. i know what you mean about mig ally.we used to do a lot of repairs builds of tipper bodys and it used to drive me nuts trying to do it ..porosity ,sticking wire ,spool guns etc etc .. for me tig welding is the way but having said that you have a bunch of lorch machines and a really helpfull chap called matt ??

 

[Jim Davey]

Get Matt back in to give you some refresher training, once you've got the prep, gas flow and settings right it's all about keeping things clean.

 

[matt1978]

Hi Paul,

Did you get some U groove rollers? Change the liner in the torch and remove the brass capillary tube?

Try it on the S rather than the P's. Call me tomorrow and I'll talk you through the set up