6061-T6 is often the alloy of choice because it has excellent as wrought tensile strength and yield strength. Elongation, not so good when it is in the T6 temper or the as welded condition (when compared to carbon steels). The two common filler metals are 4043 and 5356. If I were to make a guess, I would say the majority of aluminum alloy that is welded for structural application is probably 6061-T6 and it is welded with either 4043 or 5356. So, for me, this is an interesting discussion.
As noted, the wrap around bending fixture solves many of the problems experienced when performing the guided bend tests. As observed by a previous poster, the bends will often fail when using a plunger and die set because the HAZ is softer than the unaffected base metal or the weld, thus the bend is concentrated in the HAZ, and the bends fail as a result. The wrap-around bend fixture eliminates that problem. Another common mistake is failing to reduce the bend test samples to 1/8 inch when testing in the as welded condition. This requirement is included in AWS D1.2, B2.1, and ASME Section IX.
As for consistency between the various AWS welding standards, both AWS D1.2:2008 and AWS B2.1:2009 list different bend radii for M-23 base metals in the as welded condition and PWHT (annealed) condition. In the as welded condition both welding standards require the guided bend sample to be reduced to 1/8 inch (or less for job thicknesses). The bend radius for the 1/8 inch thick as welded sample is 2 1/16 inch (16 1/2 T for thicknesses less than 1/8 inch) in both AWS publications. Both AWS publication require full thickness guided bend samples up to 3/8 inch thick and both require 2 1/2 inch bend radius when the sample is in the annealed condition. Again, just so as not to lose track, we are limiting this conversation to M-23 (6061-T6 aluminum alloy). If the aluminum alloy is welded with an F-23 filler metal, it is treated in the same manner as 6061-T6 (M-23) in the as welded condition.
I find it interesting to note that in AWS D1.2:2008 clause 3.12.2 states that PWHT must be addressed by the WPS. Clause 3.12.1 states that the PQR must record the essential variable and references Annex F for a sample form. Yet, I find Table 3.1 does not include PWHT as an essential variable. I did find an interesting bit of information in clause
3.8.1.7 Special Bending Conditions - M23, M24, M27 Base Metals, and F23 Filler Metals. It does include provisions for annealing the guided bend samples before bending them. Whereas D1.2 does not list PWHT as an essential variable in Table 3.1, I must agree with Tom that annealing the guided bend sample is permitted for the base metals listed AWS D1.2.
Now let's switch gears for a moment and go back to AWS B2.1 which was referenced by the individual that started this thread. Clause 4.14 lists all the essential variables that apply for various welding processes, base metal groupings, i.e., M numbers, etc. Under the heading of PWHT, item 4.14.6 (2) PWHT is an essential variable for all welding processes. So, I guess there are some inconsistencies between the various AWS welding standards. In the case of AWS B2.1 I would conclude that annealing the guided bend samples is not permitted for a WPS qualified in the as welded condition. The only time AWS B2.1 permit the guided bend sample to be annealed is if the WPS is qualified in the annealed condition.
This has been a great exercise. Tom, I agree with you that if you are welding in accordance with AWS D1.2 you can anneal the guided bend samples before performing the bend tests. However, in this case, whereas AWS B2.1 was referenced by the individual initiating this post, I conclude you cannot anneal the guided bend samples if the WPS is qualified in the as welded condition. I guess one really has to study the applicable welding standard before taking a position. Once again, I have learned something new. Consistency between all the AWS standards? Not from what I just read.
There are techniques involved or should I say procedures that must be followed explicitly in order to qualify M-23 aluminum alloys or alloys welded with F-23 aluminum filler metals. Short cuts always prove to be fatal. Aluminum is one of my favorite metals. I make a good living working with contractors that must qualify their aluminum WPSs. Some chose to ignore my advice and learn the hard way, others ask me what steps must be taken and we pass the tests the first time most of the time. I have had very good results qualifying aluminum alloys, even the M-23s, over the years. I spent nearly five years working on the Aegis missile system as a welding consultant for several of the main contractors working the project. It is safe to say I learn a lot about welding aluminum alloys during that time. If it was easy, they would not need my expertise.
Tom, you did good job of standing your ground. Still, how are you annealing your samples? Are you reducing the sample thickness to 1/8 inch or 3/8 inch? And what bend radius are you using?
Best regards - Al