Biodegradable citric acid bath for cleaning aluminum.

By Lawrence (*****)

Date 02-10-2016 16:14 Edited 02-10-2016 16:23

There are a lot of citrus degreasers out there that are pretty good. As long as it is designed for this purpose there really should not be enough residue to cause the problems you are describing.

Same with any media from the water jet. While it is always possible that the soft aluminum may see some slight residue from the media via impact, I would suspect that the result would be noticeable only via RT and would look like VERY small porosity or inclusions. Any aluminum oxide media smeared into the base metal from the belt sander would also be seen as speckled porosity rather than a cause for hot or cold cracks.

What you seem to be describing is delayed cracking or "cold cracking" (days later). This is VERY unusual, and Hydrogen is not as likely to be the involved in mechanism as it might be with steel. Cold Cracking (post weld) in Aluminum is practically unheard of.

6061 (you probably know this) must have an alloyed filler metal added to avoid cracking as the weld solidifies (hot cracking). Typically 4043 and 5356 are used for this, with 4043 providing greater alloying of the two.

I recommend you take a very close look at your weld profiles. If they are flat to slightly concave, you may very well not be getting enough alloying from the filler metal and have a deposit that is susceptible to cracking. The thicker the base metal and the higher the joint restraint, the greater the likelihood this may be your problem.

It is always recommended that convex weld profiles are deposited with 6061 base metals, whether GMAW or GTAW.

I know this isn't the trail you were following, but take a second look at those profiles anyhow :)

Edit: Acetone or Toluene are preferred over Isopropyl alcohol for that final wipe down.

By Trackergd (**)

Date 02-10-2016 17:31

Thanks Lawrence!

One odd little tidbit I forgot to add. When the crater is filled (GMAW and some of the GTAW welds), there is a very small dark dimple in the center top. If you look at it under 10X, you see a cluster of little pyramids with micro cracks. The dimple is around a 1/16" in diameter. I cannot figure out what is causing it, hence my investigating contamination. It should not be aluminum oxide as that would not float to the top being the same density as the parent metal.

Currently we are using Argon with ER4043 fill.

To combat the "dimple" we have been over filling the crater, then while still hot, hitting it with a burr knocking it down to the weld profile. Even a couple of these ended up with a "crater crack". Also found one one longitudinal crack when I looked at the welds a week later in the field which I have never seen before on this particular weldment. I may cut that one apart and macro it.

We decided to get some "expert" review and have called in a specialist from the welding machine company as well as a CWI and SCWI from our local weld lab and testing service.

The only way I am going to know what contamination (if any) is in the cracked welds is to send samples out for analysis.

By Lawrence (*****)

Date 02-10-2016 18:11

Ok, now we are down to it!

That "dimple" is pretty typical with aluminum GTAW and GMAW. The weld pool cools from the outside-in. As it does there is often some shrinkage that causes the depression and star cracks.

As the aluminum weld progresses, the heat travels forward and often the weld pool grows a little larger. The larger pool requires more filler when the weld is terminated.

For GTAW (Technique)
I prefer to use the largest filler rod I can manage, and as the weld termination begins, rather than slamming off the current, ease off the foot pedal and add an extra dip or two in order to make the termination convex. Problem solved.

For GMAW
This may be a little more tricky... If you have a "crater fill" option on your feeder/power supply, you can set it to reduce current and add wire. This may require several different settings if you are working with different base metal thicknesses.
You can also "trigger" the gun after the termination to get the crater filled, but with aluminum that additional heat at the end makes this more tricky.

This really sounds like your process control issue is closer to the weld than to the preparation. But I think its going to be totally manageable for you.

By Trackergd (**)

Date 02-11-2016 16:32

OK. I had not seen that dimple in the past, but then again we are taking a much closer look at our welding processes and dealing with continued crater cracking...even when the crater is overfilled and ground down, which if I understand you correctly, puts more heat in that area and could create it's own issues.

Some of our welders use the crater fill option and some do not. I guess since we have Miller welders, I will let the Miller specialist evaluate and give me some feedback.

Still going with the citric acid bath since it is very hard to detect cracks when there is a bunch of soot and grinding dust all over the welds. I am going to insist they are clean parts before I inspect the welds.

I agree that this now sounds like a process control issue. I'll concentrate on that and still keep rolling on trying to control contamination and ensure the removal of the oxide...it can't hurt.

By ssbn727 (*****)

Date 02-15-2016 08:24

That's twice you mentioned the grinding dust... Now my question to you is this... Are some welders in the same perimeter of where the Aluminum welding and grinding is, welding and grinding steel? If so, that could be a source of contamination especially if some of the steel particulates from the grinding is falling on to the Aluminum surface and being smeared all over the weld zones where it's no longer visible... The area's where steel is being fabricated and welded should be separate from each other...

Still, I have to agree with Lawrence stating that your problem is most likely process related and he provides an excellent and descriptive set of points to consider... Too many of the points he has described are correct and makes sense as well as not to be overlooked in determining the root cause(s) of your problem.

Respectfully,
Henry

By kcd616

Date 02-15-2016 08:46 Edited 02-15-2016 08:48

Henry,
my very good friend
the problem could be the grinding wheels
ie aluminum oxide grinding wheels :eek:

both your ideas and Lars really hold water and make sense
but the Kent ideas start simple
and cheap :smile:

at the grinding disks
sincerely,
Kent

By Trackergd (**)

Date 02-15-2016 13:04

Not only are they in the same proximity, aluminum and steel are done in the same weld booths on a regular basis. The cut aluminum is stacked in the same area as the welding is done. No question that there is steel grinding dust falling on the aluminum.

Had the Miller welding expert in. The results of his evaluation will need a "wall of text" to explain. I will do so in the next couple of days.

By Trackergd (**)

Date 02-16-2016 20:50

Yes, Lawrence made all the correct points as has everyone else who chimed in. To sum up a lot of issues, it is a combination of grinding dust, incorrect cleaning materials, incorrect cleaning methods, incorrect welding technique, inexperienced welders (in a couple of cases) incorrect welder settings (way too low) for the material, incorrect weld call outs on the drawing and at least one design flaw area that no matter how we welded it, would have eventually cracked due to stress as it cooled. It was a rather sobering experience... The gentleman from Miller made all the same points you folks did.

By Lawrence (*****)

Date 02-16-2016 21:08

Now that you are sober, know this friend; Aluminum is NOT harder to weld than steel.. Just different.

When you learn the dark secrets you become a very valuable person.

The link below gives the best information I know about those dark secrets, given by a guy I trust and have depended on several times myself. Frank Armao

http://www.thefabricator.com/author/frank-armao

Read them all..... Then next time, you will be teaching that "Miller guy"

By devo

Date 02-16-2016 21:33

Having followed the advice of Al and Lawrence on here for years (always with good results), I've moved away from using SS brushes and started using a scraper for initial weld prep. Mine is just an old file, ground with a slightly positive rake, stoned sharp, and it goes much quicker with 6xxx alloys than trying to scrape that s**t off with a brush alone. A quick follow up with the SS brush makes for a nice clean result with less time and effort.
The timesaver probably isn't helping either, unless you need it for cosmetic purposes.

By 522029

Date 02-16-2016 21:43 Edited 02-17-2016 01:57

Just so you know, since Ford has started using aluminum frames and body parts, they have made their dealerships separate their "aluminum body shop" from the "steel body shop". This is due to potential steel contamination of the aluminum work in process.

HTH
Griff