Aluminum grinding dust contaminating HSLA steel A656

Date 03-30-2011 18:31

I understand very small amounts are sometimes used as deoxidizers and adds hardness, I have a situation where grinding dust from aluminum operation is covering the tacked A656 grade 80 parts that are to be welded and I'm concerned that air blowing the dust will not get it out of the joint interfaces completely. What type of concerns should I have if the aluminum dust were to be welded over?

By 803056

Date 03-31-2011 16:46

Aluminum is used as a deoxidizer when killing the reaction between carbon and oxygen while pouring steel so the formation of CO is reduced. Aluminum oxided is the byproduct of the interaction between oxygen and aluminum. The aluminum oxide has a high melting temperature (between 3200 and 3600 degrees) and acts as nucli to which the iron (and other metals) atoms anchor themselves.

There is a limit to how much aluminum can be introduced. Excessive additions of aluminum reduce toughness. Other deoxidizers such as ferrosilica and ferromanganese can be used as deoxidizers as well as aluminum.

I've have seen aluminum oxide from grinding show up in radiographs on thin material. It may not be remelted by the welding arc, thus it can remain embedded in the base metal.

I usually have the welder go over the area that was excavated with an aluminum oxide disc (thick "back gouge") with a carbide rotary file to remove just a little base metal and any embedded aluminum oxide before welding. It seems to work, but unless the base metal is soft (think monel, etc.) it is not usually necessary if the welder does not bear down on the grinding disc too hard to begin with.

Best regards - Al

By Mwccwi

Date 04-01-2011 09:38

Thanks Al,
My concerns is stopping production all together because our "King of Idiots Welding Master" employee was grinding aluminum extrusions in the HSLA steel welding bay and managed to coat every thing with a fine aluminum dust.
I'm pretty confident that the customer specifed A656 Grade 80 material for its high strength and fatiuge resistance and the introduction of aluminum into the weld could cause product failure.
Since sometimes around here the "RFI" is teated as taboo "we do not want to contact the customer because we screwed up", so with this I quarentined all of the parts that were in the powder covered bay until I can get approval from the customer or somehow be satisfied that all contamination is removed.
So far I looked in AWS/Linnert's Welding Metallurgy Vols. 1&2, Lincoln's- Metals and how to weld them and the Welding Procedure Handbook, AWS's- Welding Inspection Technology books and have not found satisfaction.

By js55

Date 04-01-2011 11:51

I am in agreement with a cautious approach because we don't really have enough information, but keep in mind every weld made is chock full of non metallic inclusions of which aluminum oxide would be one. Al (meaning aluminum not our distinguished colleague Al) is not uncommon as a deoxidizing element in filler metals because it is far more aggressive in bonding with oxygen than say manganese or silicon (for example, the very reason it is one of the deoxidizers in ER70S-2 and many many other alloys and the very reason S-2 does not have the Mn/Si levels of S-6 or S-7). In some instances non metallic inclusions can even improve mechanical properties since they can also be initiation points for acicular ferrite and improve toughness.
But in this case we simply do not have enough information.
It is my contention, as a theory of course, which is all we have right now, that your worse case scenario would actually be the aluminum more readily bonding with oxygen in the weld puddle, most of it ending up in the slag.
If you tested the weld deposit and the slag chemistry you would see manganese, silicon, and other less aggresive deoxidizing elements increase in volume percent in the weld deposit because the aluminum will have deoxidized instead, and you will see aluminum increase in the slag. What will increased Mn and Si do to the weld deposit? Most likely make it stronger.
A better volume than Linnerts for understanding aluminum in weld metal is Metallurgy of Basic Weld Metal by Evans and Bailey. Or, you can get all of the chapters as articles through IIW since the book is a collection of years of research.
This could be a very interesting study.

By 803056

Date 04-01-2011 12:42

If your concern is with the aluminum "dust"; clean the surfaces and adjacent areas prior to welding. I doubt the aluminum dust is going to bond with the surface of the base metal simply because the aluminum dust particles are going to be encapsulated by a tough aluminum oxide as soon as the hot particles are exposed to air. The dust should be easily removed by wiping or vacuuming the surfaces.

I was going to suggest, "blowing the particles off with compressed air", but that would simply make the particles airborne. Once airborne the particles will settle on something else. For that reason I would suggest simply using a vacuum cleaner to pick up the errant particles. Any foreign material that can be inhaled by workers is not a good thing. The aluminum dust isn’t going to promote the “good health” of the workers in the work space, so it is just one more vote for using a vacuum cleaner to pickup and remove the offending particulate.

By the way, nice discussion and some good information about deoxidation JS. I don't own a copy of the book by Evans and Bailey. I'll have to find a copy and add to the "mess" as my wife calls it.

Best regards – Al

By js55

Date 04-01-2011 13:55

Al,
This would be a really good study. I do not believe the OP's problem is isolated. The aluminum involved is a wild card. It would certainly have some effect, but what?
Your advice on cleanliness is certainly right on. Especially for the health issue.
And even though I do not believe there would be any actual harm, I would not act in that manner given the ignorance (including my own) here.
Also, the Evans and Bailey book is based upon SMAW but there were also some TWI papers on SAW that made similar discoveries about oxide and non metallic inclusions.
And if memory serves, though I do not swear to it since memory seldom serves, the work had tremendous fallout in how filler metals were formulated to acheive better mechanicals.
The book also spoke of titanium, again if memory serves, though for the same reason (it is more aggressive than Mn and Si) and is an excellent initiation point for acicular ferrite (and it is no coincidence that Ti also is one of the triple deox elements in S-2).
I kind of think this was an evolution not unlike the sulphur in SS issue wherein that which was originally though to be detrimental actually has great value at controlled levels. They get the stuff too clean and then find out they gotta go the other way.

PS; I have that same mess and same complaint from the wife.

By 803056

Date 04-01-2011 16:50 Edited 04-01-2011 19:59

I need to visit Amazon and see if I can get a copy of that book. It sounds like an interesting read.

Best regards - Al