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Up Topic Welding Industry / Technical Discussions / GTAW open root alluminum vee groove question
- - By SEAPLANE (*) Date 12-15-2011 00:35
Hi all, I've welded alot of alluminum over the years, But I have never had to certify on an open root vee groove alluminum test. I am welding 062 6061 with 4043 on a 1"  thick groove block fixture with an argon backing purge. I'm running 3/32 wire with a 3/32 gap and a feathered edge. Everything is clean and prepped with an alcahol wipe down. Miller synchrowave 350 with foot pedal. I'm getting a crusty look on the root side with a line of non fusion in the center. The root is broken down on both walls But it looks like the very edge of the bevel is still visible in the center of the root !
This is an xray test and other than turning it over and back welding the root side, I don't know how to eliminate the line. I also don't know if the plate is annealed or if it's in it's hardened state before I weld it. It's T6 6061. I beleive the last welder that tested for this place back welded his coupons. I have not been told not to do that, but would think it would break down easy enough from the front side with a purge on it.
The other technique I'm thinking of trying would be a square cut non beveled edge and butt both pieces up tight and then run the one side and flip it over and gouge the back side and then weld it on the backside.The WPS for this shows a squared edge/non bevel on the drawing and does not list any bevel angle. I could sure use some insight on this one! Thanks!
Parent - - By Leandro Sabino Date 12-15-2011 03:57 Edited 12-19-2011 17:01
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Parent - - By rodofgod (**) Date 12-15-2011 04:16
Hi All!

I think what Leandro is trying to describe is an 'Oxide Break'?

Open root aluminium v groove procedures are very, very rare in my experience! However, Leandro's advice is relevant!

Regards
Parent - - By SEAPLANE (*) Date 12-15-2011 21:27
Thanks for the replies . I prepped the joint as Leandro suggested in his diagram with a slight back bevel. It requires welding on front and back side. I'm sending a coupon in to shoot. I;ll let you know how it turns out! Now I have to do a Magnesium coupon. This stuff is nasty!  After the Mag. I will do some 718 inconel. I've done that one a couple of times, so I am familliar with it. The alluminum and Magnesium is a different beast!  The T6 alluminum is in it's hardened state when welded. I was wondering if it should have been annealed first? Guess I'll find out in a day or two.
Parent - - By DaveBoyer (*****) Date 12-16-2011 04:27
The T6 aluminum doesn't have to be annealed first, but the heat from welding WILL reduce the tensil & yield strength in the heat affected area. For this reason, it is good to keep heat input as low as possible, unless the parts will be heat treated after welding.

Is there any mention of minimum tensil strength after welding?
Parent - - By 803056 (*****) Date 12-16-2011 05:30
If you are welding 0.062 inch thick 6061-T6 there is no need to bevel the edges or to use a root opening. A square groove preparation with a tight root is fine up to about 1/8 inch thickness unless your welding machine is less than 200 amps.

The aluminum can be welded with AC and argon shielding gas or DCEN with helium. Most people find AC easier because of the cathodic cleaning obtained with AC.

The important thing is to wire brush the joint just before tack welding the assembly and actually welding. You should consider draw filing the groove face to remove any oxides present on the sheared or cut edges. Aluminum oxidizes immediately upon exposure to air. 90% of the maximum oxide layer forms in the first 24 hours, so it is imparative to clean the groove and adjacent surfaces just before welding.

Wire brushing should be performed with a clean stainless steel wire brush after the joint and adjacent surfaces have been cleaned with solvent such as virgin acetone followed by 90% isopropyl alcohol. Once cleaned, keep your fingers off! I can't tell you how many times I've seen welders clean the material only to contaminate it once again by running their finger down the cleaned edge as they check for burrs. Oils keep your skin soft and flexible. The same oils will produce porosity in the weld. So, wear latex gloves while washing the material with solvent, wire brushing, etc. Wear clean gloves while welding. Using bare hands to feed the filler metal only contaminates the rod with oil from your skin. Wash the rod with solvent and deoxidize the rods by rubbing them down with stainless steel wool. Never use regular steel wool. Iron and aluminum do not play well with each other.

You will typically see the line down the center of the weld on the root side of the weld even when it is perfect. It is normal. If you weld without purge, the surface will be crinkly and oxidized. Again, it is normal and not detrimental to the weld. Better results (appearance wise) will be obtained with root purge, but it will do little for the mechanical properties. They will suffer whenever you weld 6061-T6 and there is no way to get the material back to the original properties even with post weld heat treatment.  A good weld in 6061 will have a tensile strength of 24 to 28 ksi. Roughly a 40% reduction in tensile strength can be expected if the weld is made properly.

The fewer weld passes required the better. A single pass weld will suffer less degradation of the mechanical properties than a weld that requires several weld passes. 6061 is time at temperature sensitive, so if multiple weld passes are required to fill a thick groove, allow sufficient cooling time between weld passes. As a matter of fact, a fan blowing cool air across the weld area is preferred to cooling is still air. Artificial cooling is better yet when it comes to perserving the mechanical properties. DO NOT PREHEAT the base metal. If the metal doesn't flow are the ampera you are using, increase the amperage until it does flow. Preheat is not good if you are trying to perserve the tensile strength. Remember, a good weld in 6061 only has to meet 24 ksi to meet AWS D1.2 or B2.1 requirements and it is considered to be "good".

Best regards - Al
Parent - - By DaveBoyer (*****) Date 12-16-2011 06:51
Not to hyjack the post, but...

Shortly after I left Dana/Parrish Frame they started to develope the aluminum space frame for the Corvett. They came up with some process to anneal the 6061 T6 tube enough to hydroform it, and supposedly it was back close to T6 properties after 24 hours. One of My friends worked on the project, but moved away before I got to pick His brain about it. Know anything about it?
Parent - By 803056 (*****) Date 12-16-2011 16:35
6061 aluminum alloy is a heat treatable alloy that is precipitation hardened. The hardening mechanism is accomplished by heating the alloy to a high temperature to put all the alloying constituents into solution. The material is then quenched to keep the alloying constituents in what is essentially a supersaturated condition. Hardening is initiated by aging the alloy at an elevated temperature to initiate "clumping" of the alloying constituents within the atomic lattice. The clumping of the alloying constituents strains the atomic lattice thereby strengthening it. However, if the alloy is held at too high a temperature for too long a period, precipitation occurs. The alloying constituents precipitate to the grain boundaries thereby weakening the base metal. Precipitation is typically referred to as "overaging". 

Overaging is what happens when the alloy is welded. The extended time at temperature allows the alloying elements to precipitate to the grain boundaries. There can be some benefit to post weld heat treatment if the entire weldments can be heated to force all the alloying elements back into solution and if the entire weldments can be quenched without causing unacceptable distortion. There’s the rub, usually the PWHT required to recover the mechanical properties destroys the component.

In your case, I suspect the alloy is annealed by heating and quenching. The hydroforming is performed and then the part is artificially aged at a high temperature to drive the clumping action needed to gain strength. The benefits can be and will be lost if the frame is welded after the frame is formed and aged. Welding results in overaging.

The aging temperature varies from one alloy system to another. Aircraft cylinder heads used in the old radial engines were aged at ambient temperatures. The raw castings were allowed to age for up to a year before they were machined.  I remember seeing pallets of cylinder head castings sitting beside the buildings for months on end before they were taken inside to be machined into finished parts.

Best regards – Al
Parent - - By Lawrence (*****) Date 12-16-2011 17:38
I wonder if the strain/movement that occurs during the hydroforming might have a pretty significant effect on the mechanicals of the 6061..

Post hydroforming heat treatment sounds like it would have to have some super controls in order to keep geometries correct.

I did a google search and there are some abstracts out there on what your talking about, but nothing for free and nothing in my library that is totally current.
Parent - By DaveBoyer (*****) Date 12-17-2011 00:26
The parts were not heat treated after forming, I think the dislocation from hydroforming strain hardened the parts.
When they were developing that frame, it was probably propriatary information, but that was near 20 years ago.
Parent - - By SEAPLANE (*) Date 12-17-2011 01:37
This particular weld I am refering to is a test coupon that is subject to a radiographical inspection. If there is a line on the root side and it is considered normal, won't that show up as lack of fusion?
I was hoping to be able to weld the coupon from one side, But after looking at older coupons on file, I see that they have been welded from both sides. I guess that is standard practice for this test? This is a D17.1 code and a class C part that really doesn't require a qualification if i interpreted the code correctly. But we are doing the test just the same.
QC only sends the coupon out to be shot, and I will get the results in a few days. The actual work that I will be required to do will be partial joint penetration and padding welds that are machined after welding. Thanks for all the info!
Parent - By Milton Gravitt (***) Date 12-17-2011 01:57
Can't you just grind the back side of the test plate to get the line out . I know theirs a lot of people that don't believe in grinding a test plate I probably will take a lot of bad mouthing, but I don't see nothing wrong with it some times is hard to get the line out of 6061 T6.

                                    M.G.
Parent - - By Lawrence (*****) Date 12-17-2011 05:46
Listen to Al,

A D17   .063 test coupon is not typically welded from both sides.

a clean file on the root face right before welding will help get a good fusion...  The line is also typical.

Don't confuse procedure with performance in your code... ALL welders must be performance tested.. the only type of performance qualification tests are to the standards of a class "A" weld or a production mock up.

The difference in classes is focused on inspection criteria and procedure qualification.

The weld may not require qualification but the welder does.
Parent - - By 803056 (*****) Date 12-17-2011 14:48 Edited 12-17-2011 14:50
If the coupon is welded propely, there will be some melt-through on the root side. The line will run right down the middle of the root reinforcement. That area is thicker than the adjacent base metal, thus, complete joint penetration is achieved and the is no incomplete fusion. If however, the welder does not preclean the parts completely, i.e., oxides remain on the groove faces, the line will be more pronounced and the oxidation more obvious.

As for interpretation of the radiograph, the film interpretation is based on differences in film density. Darker images indicating less density, i.e., less thickness indicating a crack, incomplete joint penetration, etc. The area through the sound weld is thicker, thus it appears lighter on the film. A good radiographer should be able to discriminate between weld (lighter), base metal, darker, and unacceptable indications (typically darker).

There is no reason not to grind the weld flush if there is any concern that the radiographer will question the film due to roughness on the root side provided it passes the applicable visual acceptance criteria of the welding standard. Most welding standards (with the exception of ASME Section IX) hold the welder performance test to a higher standard than the production welds, so make sure the appropriate criteria is applied.

D17.1 is the most goofy welding standard imposed on the welding industry. Make sure you understand what it requires.

In my most humble opinion, aluminum performance tests should only be subjected to bend testing using a wrap-around bending fixture. RT will not usually disciminate between sound aluminum and aluminum oxide trapped within the weld since both have nearly the same density. Oxides don't usualy break down in the weld pool because of their higher melting temperature (above 3200 F) and they do not float out, thus a radiographically sound weld can be brittle due to oxide inclusions. The bend test will definately show you if oxides are present. Keep in mind that the guided bend test sample must be 1/8 inch or thinner. This is in contrast to most other bend tests where the standard is 3/8 inch thick. Since you are welding 0.0625 inch thick material, this is not a concern. However, the bend radius must be based on the actual thickness of the sample, the P/M/ or group  number of the base metal, and classification of the filler metal. If there is a question regarding the proper bend radius, refer to AWS B2.1 or MIL-STD-1595A. If I remember correctly, D17.1 omitted referencing the appropriate standards for determining bend radius.

Best regards - Al
Parent - - By DaveBoyer (*****) Date 12-18-2011 06:03
I am just wondering... How large must the bend radius be when You get into thicker sections of 6061-T6 ? Or do You mill the test specimin to a thinner dimension [the 1/8" You mentioned]?
Parent - - By 803056 (*****) Date 12-18-2011 15:25
All the welding standards I've worked with, i.e., D1.2, B2.1, MIL-W-8604, MIL-STD-2219, etc. require the sample to be machined to 1/8 inch thick when working with 6061 or 6063 (P23 or M23) aluminum alloys or 4043 type filler metals (F23) . ASME Section IX only lists bend diameter/radius for 1/8 inch and for less than 1/8 inch thick. No provisions are made for thicker samples. Similar information is included in AWS documents.

I always mill the samples, either removing the material from the root surface if performing a face bend or the face surface if performing a root bend.

Best regards - Al
Parent - - By DaveBoyer (*****) Date 12-18-2011 23:44
Thanks. I wondered how they handled that.
Parent - - By SEAPLANE (*) Date 01-05-2012 00:28
Well, My little coupon shot acceptable and I am officially certified to weld paper thin alluminum! I appreciate all the input and commentary on this subject.
Parent - By 803056 (*****) Date 01-05-2012 01:52
Good show.

Al
Parent - - By Lawrence (*****) Date 01-05-2012 04:36
Great..

Now tell us how you went about the test.  Which way did you do it?
Parent - - By SEAPLANE (*) Date 01-07-2012 16:58 Edited 01-08-2012 19:27
I followed the WPS! I prepped the edges of the .063 plate with a dremmel tool and small rotary file with just a slight chamfered edge. Wiped everything down with alcohol including the 4043 wire. Clamped both coupons to a grooved test fixture with no gap and an argon back purge. I used 2% thoriated tungsten 1/16" diam.The balance was set at Balanced and the amps around 60 with a potentiometer. I welded one pass and that gave me sufficient reinforcement for the cap and the penetration was 100%.
I took a scotch bright round disc and buffed the root side lightly to remove the line that was visible. It brushed to a solid root and still had a light reinforcement. That was the part that I was very curious about. I am glad you guys responded above with what was acceptable on the root side.Thank you!
Anyway, They were  sent out to X-Ray and came back acceptable. I am now waiting on the Magnesium WPS so I can get that one out of the way. We may have to qualify the Mag procedure, as there doesn't seem to be an SWPS available from AWS for this one. We will have spend a ton of money doing that . Thanks for all the input!
Parent - - By Lawrence (*****) Date 01-07-2012 19:55
"Followed the WPS"

Perfect answer  :)

I was very confident you could do this from one side.

Those groove welds can be done from one side with a normal square groove (no beveling) all the way up to 0.93, even with a zero root opening...  It takes a bit of practice.   The main point, especially with 60xx series aluminum is to learn how to go hot and fast,

Many beautiful welds fail x-ray inspections or tensiles because slow travel speed allows too much Hy to get into the weld pool, and it doesn't all escape during solidification and the extra heat buildup removes our friend T6.

Great Job!

Now post about the Mag when the time comes... I was chained in a basement for about 2 years repair welding Mag castings.   It's fun to talk about now that I don't have to do it any more  :)   One piece can weld like a dream and the next one that looks exactly the same can be a 40 hour nightmare.
Parent - - By SEAPLANE (*) Date 01-08-2012 19:24
Thanks Lawrence! I had never welded any Mag untill about a month ago. The only resource I have for tips and techniques is youtube and you guys! I have been playing around with what I assume will be the test and some old scrap castings that are AZ33 type. At first I was scared of all the horror stories of uncontrolled combustion and I am very careful to keep any shavings and slivers out of my welding area and off the floor. I'm hoping I can keep my caution up because the moment i get comfortable with it, I will surely have an uncontrolled fire! The Balance controll on my Miller Synchrowave 351 doesn't seem to make any difference where it is set at. I was used to a Thermaldynamics machine that would balance high enough to almost whistle on alluminum. I get a course sounding balance with this Miller, No matter where I set it. On the Mag,At low amperages, It wants to arc wonder all around the puddle and it causes the edge etching I was talking about in the other thread.
The Miller was calibrated a couple of weeks ago, But the balance controll was not checked. I may have to get the service tech back out to look at it. I hate a situation like this one... Is it me or the machine? I always said a good welder can come up with at least 5 excuses right off the bat! :)  On the thick material, I don't seem to have any problems as long as I have a good pre-heated case right out of the oven to weld on.
Parent - By Tommyjoking (****) Date 01-09-2012 02:47
Mag welds just like AL  never had any issues.   Congratulations on your test plate!  Most guys start struggling in that range of thickness.   I have exception with the paper thin comment tho....qualify on some 6061 .020 fillets with 0 burn thru.....then talk about paper thin!

Keep those thin tig skills going...from what I have found it is a rare talent!
Up Topic Welding Industry / Technical Discussions / GTAW open root alluminum vee groove question

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