Quote:
Originally Posted by JamesCH95
This is not always true.
While the weld should be designed to be stronger than the base material, this isn't always the case. Frequently teams will make parts out of 6061-T6, but when welded 6061-T6 turns into 6061-T0, and the welding rod alloy (generally 4043) won't ever be as strong as the parent material, even if it's re-heat-treated. The weldment must be designed to take this into account.
The trick here is that the HAZ (heat affected zone) near the weld is still parent material thickness, but has been annealed by the welding process, and is thus weaker than it used to be. This is where most failures will occur. While the HAZ is not precisely the 'weld bead' itself, it is part of the weld in a holistic sense.
To address the 'bolts are always stronger than welding' stance some people have... It depends, on a lot of factors. They each have their place. To point out one specific example in FRC: welding the old C-Channel kit frames saved about 3lbs in brackets and fasteners and resulted in a stiffer, stronger chassis. The C-Channel was 5052 alloy, no heat-treatment and thus no strength loss when being welded.
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I think that is where the "properly" and "correctly" come in to play. If you are welding an item for heavy use, you had better be sure that you are using the proper materials. In the 6061 case that you mentioned, the wrong materials are employed if they aren't up to the task that is placed upon them. All these alloys and issues raise all kinds of things that I don't even like to think about...
Personally, I love steel.