Cracking in base metal aluiminum (MACROS included)

Date 12-01-2015 18:50

Textbook quality macros! Beautiful grains. I'll bet you could blow those up, slap on a frame, and sell em to the artsy rich community. When it comes to aluminum, I can only speculate. But I suspect travel speed/heat input may be a factor, in addition to technique.
100% Argon?

By Trackergd (**)

Date 12-02-2015 11:48 Edited 12-02-2015 11:52

We are have having the exact same issue with 6061 using 4043 filler, only we are joining sheet to sheet. I am seeing every discontinuity in the book, crater cracks, lack of penetration, lack of fusion and base metal cracking. Even had one of those welds that looks like a caterpillar crawling down the joint, if you tap on it hard, you can break it off... First we had some animated discussions about technique, then we tried changing the filler to 4047 with some success, now we are trying different mixtures of argon/helium to see if that helps any. Nice pictures!

By jwright650 (*****)

Date 12-02-2015 12:07

I agree with the others...those are great pictures. I find it interesting that several of those joints with fusion problems at the root didn't crack. I would have thought those had every opportunity to initiate a crack.

I suspect that when adding filler it cools the puddle just off enough to prevent the cracking, as it may be a really fine line regarding that point where shrinkage overcomes the strength of the material....and you may also be on to something regarding the way the welder starts his puddle.

By Lawrence (*****)

Date 12-02-2015 12:29

I would look at two things to start.

Concave fillet profile

Travel speed

Porosity can come from a million things with aluminum... I'm callin Hy pickup.

Starved puddle wants more filler.

I'll wager a flat to slightly convex profile solves the cracking and increased travel speed solved the porosity

By ssbn727 (*****)

Date 12-03-2015 06:41

I have to agree with Lawrence on calling Hydrogen Induced Cracking otherwise known as "HIC" or Hydrogen assisted cracking "HAC"
What are some of the most common causes to this problem? It's important to note that the Ionic/atomic hydrogen that is entrapped in Al as a result of the presence of water, and/or hydrocarbons is not the same as dry gaseous Diatomic hydrogen gas originating from a pressurized cylinder... In other words, Ionic/atomic hydrogen is much smaller than normal diatomic/molecular hydrogen mainly in size... The smaller of the two types is the Ionic/atomic gas that is usually segregated from either moisture or some form of hydrocarbon and then diffused into the metal... When ionic hydrogen is produced such as during arc welding, or welding in a wet environment, it may indeed cause embrittlement of both ferous and non-ferrous metals... Certified welders prevent this with proper techniques such as cleaning, preheating and keeping their work pieces dry during welding... A properly constructed steel pipeline that currently caries natural gas can also transport hydrogen without a problem...

Here's a short list of possibilities:

1.) Humid environments and condensation or puddling of water on the surfaces over a period of time of the base metal to be joined and the same goes for the treatment of the filler metal and it's exposure to a humid environment, or becoming wet on the surface also...

2.) Shielding gas dew points is too high usually from excessive moisture mixed with the shielding gas resulting in atomic hydrogen diffusion into various metals...

3.) hydrogen from any type of hydrocarbon such as: grease, oils, water based cutting fluid used in machining some cleaners that don't really degrease the metal, and instead introduces a very thin layer of hydrocarbons on the surface... I would like to discuss this further but, I need to hit the bunk because I need to be ready by 6AM to go for dialysis treatment so I need to stop here...

Below are 3 websites and a book recommendation that get down to the nitty-gritty of some modelling methods used in prevention as well as studying the mechanisms which result in HIC or HAC. :eek:

http://www.slideshare.net/tkgn/hydrogen-damage?related=1

http://www.vsgc.odu.edu/src/Conf2010/Grad%20Papers/Francis%20-%20Paper.pdf

http://arxiv.org/pdf/cond-mat/0503483v1.pdf

"Welding Metallurgy and Weldability" by John Lippold and, The Welding of Aluminum and Its Alloys by Gene Mathers:

http://www.amazon.com/s/ref=nb_sb_ss_i_2_18?url=search-alias%3Dstripbooks&field-keywords=welding+metallurgy+and+weldability&sprefix=Welding+Metallurgy%2Cstripbooks%2C250 Lippold

http://www.barnesandnoble.com/s/welding+metallurgy+and+weldability?_requestid=255972    Lippold

http://www.amazon.com/Gene-Mathers/e/B001KIKB0A    <------- Mathers
   /
http://www.barnesandnoble.com/w/welding-of-aluminium-and-its-alloys-gene-mathers/1101586491?ean=9780849315510

Respectfully,
Henry

By MRWeldSoCal (***)

Date 12-03-2015 18:58

Thank you so much Henry! Just What I was looking for!

Jordan

By MRWeldSoCal (***)

Date 12-03-2015 19:13

Why though if you try to do a fusion weld on 6061 it cracks without filler metal added? what is happening when you add filler that cause the bonds to better form? Is it simply adding new material or is it something specific in the new solution that is reviving the bonds in that matrix?

Jordan

By aevald

Date 12-03-2015 19:36

Hello Jordan, "VERY SIMPLE" answer here: "liquification" of the base metal causes a migration and clumping of certain elements that are generally evenly "dispersed" in the metal and I believe that there is also a "loss" of a certain needed component through volitilization in the arc, upon cooling a crack will almost always occur and if it doesn't show up the weld bead will still be prone to giving out in short order. Filler metal addresses these conditions by re-introducing necessary components to the weld bead.

I know that there are others on this site that can very specifically describe this and in a much more accurate manner, likely they'll chime in here and correct me as needed. Best regards, Allan

By MRWeldSoCal (***)

Date 12-03-2015 21:32

Thank you very much for your input Allan, I think I am to that point of understanding but I want the not as simple way too I think haha. Id like to know what goes missing and what exactly is replaced. Why does it go missing? What atomic form is the solution when it begins to crack? Im at the edge of the rabbit hole ready to jump in it!

Jordan

By aevald

Date 12-03-2015 22:20

If you go the search function on the forum here I'm pretty sure that it has been discussed and has that sort of detail. It's been a long time since I followed it and so I can't remember off the top of my head what the heading was or anything like that. After looking a bit myself I found a little something that might address your question more readily.

http://www.thefabricator.com/article/aluminumwelding/aluminum-workshop-welding-6061-t6-without-filler-metal-choosing-shielding-gas-for-gmaw

Best regards, Allan

By Lawrence (*****)

Date 12-03-2015 23:20

understanding the mechanisms is important.

But when the rubber meets the road: If you increase the travel speed and make the fillet profile flat or slightly convex according to the required leg size... Your cracks will vanish I'll wager.

By Don56

Date 12-03-2015 19:38

I'm no wizard when it comes to welding aluminum, but I know it has to do with the chemistry. That's why you don't use 6061 filler metal to weld 6061 base metal. You'd have the same cracking issues.

By 803056

Date 12-04-2015 03:55 Edited 12-04-2015 04:02

Sorry I couldn't download the macros. The connection here in the hotel is painfully slow.

From the conversation and the description I would suspect the welder is not adding sufficient filler metal to fully dilute the weld. 6061 cannot be fusion welded using typical autogenous fusion welding process such as GTAW and GMAW because the silicon segregates along the grain boundaries through a precipitation process.

Filler metals typically used such as 4043 and 5356 dilute the base metal, i.e., alloys with the base metal that admixes with the filler metal, to prevents silicon precipitation.

6061 is heated to a high temperature to allow the alloying constituents to go into solution. The base metal is then quenched to prevent the alloys from come out of solution. What you have after quenching is a supersaturated solution. The base metal is then aged either naturally or artificially. Artificial aging is faster and more predictable. The supersaturated solution is heated forcing the alloying constituents to "clump" within the atomic lattice. The clumping of alloying constituents distorts the atomic lattice which causes it to be strengthened. Anything that distorts the atomic lattice strengthens the alloy. One can cold work the base metal or add alloys to the base metal. Either mechanism or a combination of both distorts the atomic lattice and presto - the metal alloy is stronger.

Fusion welding overages the heat treatable aluminum base metal in most cases. Overaging simply means the alloying constituents that are clumped together have an opportunity to precipitate to the grain boundaries and causes weakness along the grain boundaries.

Using the proper filler metal and ensure the proper amount of dilution (base metal mixing with the filler metal) prevents the precipitation or at least mitigate precipitation by forming an alloy that differs from both the undiluted base metal and the undiluted filler metal.

In all cases, heat treatable aluminum alloys suffer a degradation of the mechanical properties in the HAZ due to overaging as a result of fusion welding. Those mechanical properties can be partially recovered if the weldment is heated to a high temperature forcing the alloys in the HAZ to go back into solution. Then the weldment is quenched, often in glycol, and then it is aged to force clumping within the atomic lattice. The problem now is, what happens to the properties of the diluted weld metal? The chances are good that the alloy of the weld will not respond to the HT in the exact same manner as the HAZ.

Fun stuff!

Best regards - Al