This part is made from 6061-T6 aluminum and welded using a 4643 filler with no post weld heat treat. Why the 4643 was chosen in the first place is beyond me. I went to the design engineer and asked if I could switch the filler to the much cheaper 4043 (4043 5.31 a # and 4643 21 dollars+ a #) He said he based his decision off of some chart that had 4643 shear strength at 13.5ksi and 4043 shear strength was 11.5ksi. He told me told me that this fillet weld failed in shear because fillets always fail in shear so we have to keep the same wire. The part withstood 20,000 psi before it failed which is well above what it was designed for according to the engineer. He is afraid that if we change wires that it would fail below 20ksi somewhere and he would loose his 2 to 1 safety factor. I understand where he is coming from, but I don't think he will loose his 2 to 1 safety factor. For one, the welds on the part that failed were absolute Sh!t. No penetration to the root, lack of fusion everywhere and undersized welds.
Now, here's my take. I've never seen 4643 used in a chart for welds in the as welded condition because it is used for post weld heat treat applications. I was able to get our procedure qualifications to pass in the as welded condition using the 4643, but tensiles went at just above 24ksi. I also did a procedure qual with 4043 in the as welded condition and it's tensiles went at 25ksi almost 26ksi. Now you look at any chart for 6061-T6 welded with 4043 in the as welded condition and tensiles are supposed to be at 27ksi. Needless to say I don't go by charts that often. I know I know, you think I must have did something wrong while welding up the sample, like it must of got to hot or something. Well, we welded it really slow to allow interpass temps to get well below what they were supposed to be because I knew it was going to be a pain to get this thing to pass in the as welded condition. So what do ya think about what I got cookin here?:-)