aluminum vs steel - strength question (help please)

You are way overtthinking it.

Think about it this way how many aluminum tool boxes have you seen in the beds of old beat up pickup trucks and how many of them have steel hinges.

 

Ahh kinda....before you weld it you can drill tap, & machine fairly easy...after welding ....you may want to have them annealed first...When I was building motorcycle frames, I had some tapped bushings that would get welded to the tubes...I forgot to tap one the full depth....4 taps later it was done...I would just use plain old cold finished steel (1010-1018) amd call it a day. Aluminum will work but it does have a service life, and if it is highly stressed I would go with the 7075 siries , which is non weldable...Shawn

 

Thanks for all the input. I decided to go with 3/8" - A36 thick steel. I may drill them to remove some weight.

 

We use 7075 t6 to make our own ar15 lowers. I have one that has a 50 cal bolt action upper on it. And it handles it fine.