AWS D1.2 Aluminum welding procedures

By yojimbo (***)

Date 12-10-2013 17:14

Thank you for your responses gentlemen, both of which reiterated the standard reasons for the absence of pre-qualified welding procedures in aluminum that I had discovered prior to posting. But let me play devils advocate here for a minute because while I appreciate the points the argument against prequalified WPSs for aluminum that are being made I think there is a logical rebutal to them.

If 6061 aluminum, as an example, can be qualified to D1.2, following PQR X, using filler metal X and staying within the listed essential variables while following whatever joint preperations are required in the notes, then why can't that PQR X be substantiated by AWS, and listed as a prequalified WPS?

The arguments presented seemed based on following a WPS to the letter because aluminum is so tricky. That doesn't preclude the WPS from acceptance as prequalified. One could use any prequalified WPS from D1.1, make a mess of the welder qualification test and have a weld coupon that fails. That wouldn't invalidate the WPS, just the test coupon.

I think it is a logical conclusion then to state, IF a WPS CAN be qualified for aluminum to D1.2, THEN a FEW of the more common aluminum alloys, using a few of the more common weld processes/fillers/gases/parameters/ect. could/should be established as prequalified by AWS and released for acceptance. If they are then followed to the letter a welder should be able to produce a weld meeting the requirements of D1.2. If the welder fails to produce a weld that meets those requirements it doesn't invalidate the WPS, which has been demonstrated to work.

Actually, the argument against prequalified WPSs for aluminum seem a little sketchy, almost as if welding aluminum will only produce sound welds if certain mysterious powers have been satisfactorally compensated with voodoo sacrifices. Surely science can overcome such restrictions.

And Aaevald, can you give me any insight as to how WABO used to have a welder qualification for aluminum but no longer offers that? How did they offer it in the first place and why/when did they retract that offering. It's another bone I'd like to pick with those guys in Olympia.

Look forward to your responses. Thanks.

By 803056

Date 12-10-2013 18:06 Edited 12-10-2013 18:09

Evidently the majority of the people on the committee feel prequalification is not appropriate for aluminum.

The philosophy of prequalification entails the use of base metals with a history of successful use when a prequalified welding process is used, a matching filler metal is used, and specific techniques are used.

Aluminum doesn't have a long history of successful use as a welded material. It is almost a metal.

Minor changes in the cleaning regiment can make a difference in success and failure. A change in interpass temperature can make the difference between success and failure. There are a number of elements that if changed intentionally or inadvertently can result in substandard welds. Unlike carbon steels, they is little forgiveness when welding aluminum alloys. The looks of the weld bead may very deceiving.

The thought is, you can use aluminum in a welded structure if you can demonstrate you can do it successfully.

Personally, I like aluminum. It has provided me with a steady income because people do have such a difficult time welding it and meeting the code required mechanical properties.

Best regards - Al

By aevald

Date 12-10-2013 20:30 Edited 12-10-2013 20:37

Hello yojimbo, yes, you are absolutely correct in noting that WABO used to offer qualifications/certifications for aluminum welding. And, you are also correct in that they retracted that provision. When I was first qualified as an examiner they did have the provisions with WABO for aluminum, then they issued statements that they would no longer offer that feature and that anyone who had one and kept if current would be "grandfathered in" and be allowed to keep it as long as they kept up on their renewals. I honestly don't know if there are still those out there who are currently "grandfathered" or if they have dropped it completely, I didn't ever do any testing/qualification for aluminum when it was offered. I believe that the retraction occurred around 92/93 or somewhere in there, I don't honestly know if that date/time coincides with AWS's stand on the matter.

Now for my attempt to reason through some of your other questions. Since we are speaking of either GMAW or GTAW likely, possibly SMAW to a very small extent. With the GMAW process we have the possibility of operating in parameters where there could be short-circuiting transfer, globular transfer, spray transfer, and recently, pulsed transfer or propietary pulse transfer. This information alone presents the first issue of the welder being able to qualify for the "certification". Do we require a single performance qualification test, do we "assume" that a weldor can weld to alternative WPS's after successfully welding to one, do we have to adminster all of them, or do we simply qualify based on the applied process and limit the welding certification to a specific application/process with a specific WPS? How would you generalize the process and provide proof that it would work? I believe this is one of the main reasons for the lack of a "prequalified". Just calling out a joint design and GMAW with a specific WPS for 6061T-6 aluminum wouldn't ensure that the completed weld would meet engineering requirements. I have based this final statement on the additional "recipe requirements"(joint cleanliness, preparation, ambient temperature, preheat, wire diameter, similar or varied thicknesses) to make successful aluminum GMAW welds.

GTAW of aluminum can be even more tricky with regard to keeping everything on an even grid as far as repetitiveness and conformity. In this case, a weldor can travel fast or slow with respect to weld progression and depending on this aspect alone can possibly overheat or soften the metal in the weld zone. Additionally, filler metal diameter choice could arguably have an effect here as well. A large diameter filler could aid with reducing heat input by acting as a heat sink, whereas, a smaller diameter filler might promote a slower progression, more heat soak in the weld zone and hence result in a larger or more pronounced annealing condition of the overall weldment. Throw the various "arc characteristic" choices into the mix with the newer inverter type machines and you can see even more differences in finished products.

I believe that one of the biggest things that goes on with aluminum is the things that you "can't see". Do X-ray testing, visual inspection, UT, Die-penetrant or other non-destructive inspection/testing of aluminum weldments and everything may "appear" to pass muster. Start checking tensiles and using other types of strength/elongation type testing and you will likely notice a huge difference in the results.

It is this particular issue that I believe has brought AWS and others to remove the prequalified status for aluminum. As you already eluded to, even if there were prequalified WPS's to cover some of the common basic configurations for welding aluminum there is still no guarantee for the correct results everytime. As with any welding, a lot of things have to be done correctly to achieve the optimum results. Everyone has to do their part, the engineers, metallurgists, fitters, weldors, qc folks, inspection, etc.

Well, you've certainly heard enough from me, hopefully some of the better educated folks on here will chime in with additional and likely more accurate information. Thanks for the great topic yojimbo, got my grey-matter active, that's a good thing. Best regards, Allan

P.S. I just re-read your post, when WABO retracted/dropped the aluminum component there was no formal explanation or statement for why. I was certainly very green back then and didn't even think to inquire as to why. As I mentioned, I also was not involved much with the welding of aluminum in a structural sense, the majority of my experience was on aluminum products.