Welding Tips and Tricks

I'll start by saying that I have no scientific proof for any of this, it's just what I garnered from reading enough on the interweb to make my eyes blead. Someone stated,and others agreed that Aluminum was hygroscopic and this led me to search the web to see if this was in fact true. After finding myself 30 pages deep in a Bing search I came upon my own response to the post in this forum and that was where my search ended, I figured I'd gone full circle.

I ask that anybody who has done their own research and have found anything contrary to what I have found to please bring it to the table. I welcome being corrected if I have it wrong, except spelling and grammar, I know I suck in that regard, so don't rub it in.

I've learned quite a bit about Aluminum and it's different compounds. Aluminum is an element but is never found free standing but always in compound. The compound that is most important to this discussion is Aluminum Oxide and it is in fact hygroscopic but the alloy itself is not in the true sense, so the answer to the question has to be yes and no. Most of the other compounds are known as Aluminum salts and are not found in Aluninum as an alloy.

As Aluminum is exposed to Oxygen it develops an Oxide layer that's around 4 nm thick when new and slowly grows with exposure. This Oxide layer is hygroscopic because of it's pourus nature and does hold moiture. Aluminum Oxide is actually misted with Gold particles and used in most electronic moisture analyzers by measuring impedance across the two to measure the amount of moisture in a gas.

The Oxide layer needs to be removed either chemically or mechaniclly before welding for critical welds. Reason being is since it's nature to hold moisture and the fact that as an Oxide it's much heavier than the molten alloy it's attached to will cause it to be introduced into the weld puddle. It's melting temperature of nearly 3 times that of the base metal means that it will not be melted in the weld puddle. On new Alluminum the cleaning action of ACHF is enough for non-critical welds for this to cause little consequences.

The one thing that should be noted is that if the Oxide layer is not removed it can lead to Hydrogen embrittlement of the weld because the moisture that's trapped in it wil bring Hydrogen into the weld and it gets suspended in the fast freezing metal and forms porosity which can lead to hot short cracking. From everything I've read, I'm led to believe that the Oxygen that is introduced to the weld from the moisture may be what causes the dull surface and grainy appearance in the form of Oxides within the weld.

It also should be noted that Anodising actually increases this Oxide layer in thickness so it presents a whole other set of circumstances which would compound the problems mentioned here. We'll leave that for another day.

One cool side note from all this is I learned quite a bit about the town that I live in from all this. Charles Martin Hall, one of the original folks to develop a way to extract Alluminum from Bauxite started a little company called Pittsburgh Reduction Co. that quickly out grew it's space in Pittsburgh and had to move to a larger building in my town. In New Kensington, my town, he started what turned into a company most of you might recognise, ALCOA, then later to include ALCAN. GreinTime was born about 2 blocks from the birthplace of the Aluminum Industry, a couple of years later though.

Len

Len

Great information, well researched and presented, but I really dig those historical facts like the birth and nurture of a company, especially when you find that so much invention actually happened in your own back yard. Gives you a good feeling, eh?

Thanks for sharing

Trev

Please don't read this as argument. It is a question. If water boils away at 210 D. and aluminum doesn't melt until 1200D. how is there hydrogen in the weld?

There are millions of things I know enough about to be dangerous, but not enough to be of value. A fluorescent bulb ionizes a gas that is otherwise inert. It does so by throwing electrons off a cathode, like, but thicker than, an incandescent filament. It does this at instantaneous high voltage. Once ionized, (made unstable by an imbalance of electrons and protons in the atoms), low voltage current can freely flow. A TIG welder does this on the EP half of the cycle knocking off the oxide layer in doing so. As oxide of aluminum is a poor conductor of electricity, a heavy oxide layer severely hampers the initiation of the EP half cycle arc, making cathodic cleaning ineffective. HF helps maintain ionization of the shielding gas, or square wave power switches polarity so quickly ionization, therefore conductivity is not lost. I often feel my cleaning methods have been very effective, yet I get black gunk boiling out of the pool. If I'm not flawless in technique dipping filler, a gray ball forms. Within the cloud of shielding gas, where does this black ooze come from? What is it?

Bill,
Now this is just a theory but I would think that the Argon being heavier than both Hydrogen and Oxygen that the blanket of Argon would keep them from escaping. When water boils the Hydrogen and Oxygen separate but they don't evaporate so they're both still present. Plus there's also a strong Hydrogen bond within the Aluminum's grain structure, but that's getting way beyond my research and pay grade.

If I knew that I was going to have to answer all these questions at 50 years old I would have paid more attention in science class. I was the one saying under my breath "when am I ever going to need to know this crap" when the chemistry teacher was talking.

I think that the black specks that are in the puddle are the silicon that's used in the alloy and maybe other impurities that are fluxed from the metal itself.

Len

@Trev,
I terms of industrial history I live within a mile of the first PPG glass plant which is almost directly across the river from the first ALCOA plant that I spoke of. Pittsburgh was the birthplace of USS and many other companies. Locally they say that our glass and steel built the modern world. I live less than 2 hours from the first producing oil well. The engine for the Wright brother's plane had the block cast from ALCOA's Aluminum, found that out last night.

But one thing that still amazes me is that I can sit at my desk and answer and ask questions of a person in Australia, like yourself, in almost real time. That's amazing to me.

Len

Yeah, thank god for Al Gore, the inventor of the internet.

Bill Beauregard wrote:Yeah, thank god for Al Gore, the inventor of the internet.

I thought he invented the overheated polar bear?

MinnesotaDave wrote:

Bill Beauregard wrote:Yeah, thank god for Al Gore, the inventor of the internet.

I thought he invented the overheated polar bear?

Nope, internet and the Prius.

Man I used to troll a kid so hard about Al Gore inventing the Interwebz lol. He used to get soooooooo mad it was hilarious

Bill Beauregard wrote:... If water boils away at 210 D. and aluminum doesn't melt until 1200D. how is there hydrogen in the weld?

Water, in the arc, does not boil, per se. The oxide layer reaches a few thousand degrees with water trapped, and the arc is in the "surface of the sun" range, which disassociates the water into Hydrogen and Oxygen ions (plasma), not atoms. As aluminum in pure form (not to mention high temperature) is highly reactive, I have little problem seeing hydrogen ions mixing in the puddle, and attempting to attract anything in an alloy with a negative valence to combine, while the free oxygen ions will gladly glom on to the atomic aluminum.

A strong argument for basing the cleaning of a weld on the purpose of the weld, I suppose.

Steve S

Otto Nobedder wrote:

Bill Beauregard wrote:... If water boils away at 210 D. and aluminum doesn't melt until 1200D. how is there hydrogen in the weld?

Water, in the arc, does not boil, per se. The oxide layer reaches a few thousand degrees with water trapped, and the arc is in the "surface of the sun" range, which disassociates the water into Hydrogen and Oxygen ions (plasma), not atoms. As aluminum in pure form (not to mention high temperature) is highly reactive, I have little problem seeing hydrogen ions mixing in the puddle, and attempting to attract anything in an alloy with a negative valence to combine, while the free oxygen ions will gladly glom on to the atomic aluminum.

A strong argument for basing the cleaning of a weld on the purpose of the weld, I suppose.

Steve S

Steve;

You mention aluminum oxide as containing water, does that mean clean aluminum has none, or little?

What I've read and heard since I last posted on this topic suggests that aluminum and it's alloys have too tight a molecular structure to allow water molecules in. I'm not calling that the "final word", but it's what I've been finding.

Aluminum oxide, OTH, is permeable, or color-anodizing wouldn't work.

Steve S

Good write up Len.

I did some research too and was really surprised how little information I found with google Some articles said that aluminium is hygroscopic in some ways, but nothing more and some articles didn't mention of it at all. I'm not very satisfied with my search yet, but these aren't things that you just read in 5 min and that's that, right?

Anyway as said Aluminium itself is not hygroscopic, but oxide layer is and here is the fun part. Once oxide layer is removed it will renew itself in one second or so. In other words oxide layer is always present! Why to clean it then? Simply because it tends to absorb moisture in time, so it's always better when oxide layer is as new as possible = contains minimum level of moisture etc.

Then to hydrogen. Some of it, but not all will burn away. When there is much of it. Hydrogen will appear in the weld as bubbles, which itself are not that big deal. Problem is when the hydrogen atoms moves away from aluminium and leave dislocations to structure. Which can cause cracking. (I believe so, but need to find more facts to this).

At this point I would like to point out that hydrogen atoms tends to diffuse in time, even through a thick steel.


Here is a good catch about porosity from AGA's guide:

Porosity
Porosity causes much concern despite the fact that, unless
it is severe or aligned, it usually has less effect on weld
strength than other defects. It is rather easily detected
through standard radiography and thus has become a
highly regulated defect. Porosity is caused by hydrogen
gas trapped in the metal as itcools. The sources of
hydrogen are many, such as moisture and dirt (oil and
grease). To control porosity, it is essential to eliminate
these contaminants by correct metal preparation and
control of the welding procedure. Welding procedure is
important; the longer the weld remains fl uid, the greater
is the opportunity for the hydrogen to escape. For this
reason, TIG welds usually have less porosity than MIG
welds. The shielding gas, regardless of composition,
should therefore have a purity of at least 99.95% with the
lowest possible moisture and hydrogen content.

Btw it's Aluminium, not aluminum

4AhZ8503WPs

OK, since we're bringing up subjects of question, if a single Hydrogen atom gets trapped in a compound such as a metal, is it still Hydrogen since Hydrogen is diatomic?

@Markus, cool video, and I for one have an easier time pronouncing Aluminium than I do Aluminum. For what it's worth, it auto corrects to Aluminum.

Len

Since I'm a part of this forum i would like to say few things too , while you weld aluminum there are also strong
electromagnetic forces ( due to high currents involved ) .So if the area is a bit oily close or moisture by to the puddle due to the heat eventually will evaporate and then it will orientate with negative and positive charges this will attracted in the base metal . I'm not a science to analyse it but I have seen it happen . The worse bit and most difficult is
when you weld thick cylinder heads where the gasket seats it is must not for any porosity , what do you do them to eliminate
it .CLeanig and Heating to a good degree helps do you know something else ?
ESENTI

Otto Nobedder wrote:What I've read and heard since I last posted on this topic suggests that aluminum and it's alloys have too tight a molecular structure to allow water molecules in. I'm not calling that the "final word", but it's what I've been finding.

Aluminum oxide, OTH, is permeable, or color-anodizing wouldn't work.

Steve S

Wouldn't that also depend on the production method?
Say cast aluminum vs rolled or whatever?
Really don't know, just asking.

Sent from my SM-T537R4 using Tapatalk

Otto Nobedder wrote:What I've read and heard since I last posted on this topic suggests that aluminum and it's alloys have too tight a molecular structure to allow water molecules in. I'm not calling that the "final word", but it's what I've been finding.

Aluminum oxide, OTH, is permeable, or color-anodizing wouldn't work.

Steve S

Wouldn't that also depend on the production method?
Say cast aluminum vs rolled or whatever?
Really don't know, just asking.

Sent from my SM-T537R4 using Tapatalk

Braehill wrote:OK, since we're bringing up subjects of question, if a single Hydrogen atom gets trapped in a compound such as a metal, is it still Hydrogen since Hydrogen is diatomic?

@Markus, cool video, and I for one have an easier time pronouncing Aluminium than I do Aluminum. For what it's worth, it auto corrects to Aluminum.

Len

I don't know if hydrogen atoms actually bond with aluminium atoms in the lattice. In the other hand aluminium is a strong oxidant and it is used in stainless steels to trap free oxygen atoms, so that in mind it is possible.

Also I doubt that one or two hydrogen atoms does not do a thing, but when it is in form of gas and trapped between grain sturctures. Then we may have problems.


To Essenti
I dont know, but I would drop the hole part in to asetone bath and clean it with ultrasonic machine.

Marcus , I speak out of my experience , old aged aluminum , you weld it carefully we talk for expensive parts where there is no room for mistakes . You find babbles in the form of void in base metal of porous structure and you insist to remove it, ( you have done all sorts of cleaning even sand blasting ).It might have been hydrogen entrapped in force casting when the piece was cast. This is problem with no easy solution.
You insist and keep the puddle liquid and wide so gas can escape or the porous created , working on it . You boil base metal with a strong arc , you stop ,you boil it again and eventually it escapes , sometimes it explodes locally and you do it all over again.The same thing happens in the edge of where you weld and the base metal .This has nothing to do with skill or machine . ESSENTI..

What about solidification btw? Aluminium solidifies in around 660 °C and hydrogen in −259 °C. So it's in form of gas in room temperature with ease.

I think! So just one point of view, but not fact.

Markus wrote:What about solidification btw? Aluminium solidifies in around 660 °C and hydrogen in −259 °C. So it's in form of gas in room temperature with ease.

I think! So just one point of view, but not fact.

Then also why aluminium and even steel traps hydrogen gases, but austenitics stainless steel don't? Due to density of metals?

Bingo!!!

http://www.aws.org/wj/supplement/WJ_1974_03_s97.pdf


So far we know that aluminium itself isn't hygroscopic, but oxide is. Done! Next why it traps hydrogen and what it cause in the weld? Soon we will have an answer for that too. Within a week or two, I hope

Here is my very limited knowledge on the subject... The Austenitic grain structure traps the hydrogen. It can escape to cause delayed hydrogen cracking. This is why we use austenitic consubles (309, 312) on hard to weld steels. Speaking from a little experience and more from a spiel given to me by a former supervisor (who was a bit of a fruit loop) so it may be way off.

Mick

Have you ever seen hydrogen atoms coming out of the weld? Checkthis out, it's amazing

bv9ApdzalHM