I have this cracked Colt A1 upper receiver...

Can this be fixed / welded ?

Is there a certain way it should be fixed/welded ?

Thank you for your time

JB Weld? Not even sure if it'll hold up.

6061 can be welded, but I thought uppers were 7075 (which can't be).

It could be repaired by rare gas welding and then machining the repair back to the correct profile. then the repair would have to be refinished. Any welding shop that handles aircraft part welding will have the correct set up, I would bet anyone that does ship/boat or builds racing cars/trucks would have the correct equipment also.  There is a list some where here on the forums that had a couple companies that do Colt type receiver finish.  The real question is cost?  I bet in the end it will be much cheaper to purchase a Colt upper on the EE the next time one is listed, might be cheaper to buy a complete SP1 upper for that matter.

HERE is a complete upper..

Cheaper to replace than to have it fixed.

How did you manage that?

Could it still be used in a .22LR build anyone think?

Sure.  6061 can be welded.  7075 should be soldered, from what I'm reading.  A bunch of these just made it to market, and everyone who bit has the same problems:

www.weaponeer.net/forum/forum_posts.asp?TID=22863

http://www.ar15.com/forums/t_3_123/679929_has_anyone_been_able_to_weld_up_one_of_the_Royal_Tiger_A1_uppers.html

Someone who claims to have done it, albeit it might have been 6061:

http://www.ar15.com/forums/t_3_4/680224_Bolting_your_upper_to_a_lower.html&page=1#i6948905

You got one of these?  http://www.royaltigerimports.com/product-p/00053.htm

Start with a fresh upper.  No good reason to repair one to shooting condition that I can think of.

Yes it can be fixed. Is it worth doing it, no not really. Get a new upper receiver

Welding comments on this site make me face palm. Please, if you don't know what you're talking about, don't spread misinformation.

What the hell is "rare gas welding?" And aluminum is not typically soldered outside of electronics. Special applications, maybe; repairs, no.

I don't know what that upper is made out of. Newer ones are 7075 typically. The only way to truely know is have it tested.

When speaking of weldability of aluminum alloys in general, not receivers: 7075 is considered "not weldable." This is true for the entire 7XXX series as well as the 2XXX series. Why? Because these alloys are highly susceptible to hot cracking and stress corrosion cracking. Now, the term "not weldable" doesn't mean you can't place a bead on it or that it will crumble to pieces if attempted. It means the industry has deemed these alloys not sutable to be welded because of the two issues listed two sentences ago. These alloys are not to be used in structural applications where welding would be required. 6061 is welded all the time, it's a very popular alloy. Your next issue is the temper of the material. When you weld a tempered aluminum (usually t6 in off the shelf 7075 or 6061) you revert that temper back to T0 state. This affects the mechanical properties of the aluminum.

With all that said, could you Weld a 7075 receiver back together? Absolutely. Would it crack at the microscopic level? Yes. Would your eye ball notice or would that even matter in this relatively low stress application? Doubtful. Also, Receivers can be thin in places and could be difficult to weld if the welder is not skilled.

Looking at the costs, paying someone who knows what they are doing to weld, remachine and refinish the upper. That's going to put you in the realm of or over the cost of a new part.

Everything Hertz said. JB weld isn't going to do any good there. Hell devcon won't do any good there. Maybe for a .22 LR build, but for the price you can pick up a new upper I wouldn't bother.

I would not use a cracked upper for anything except a display.  I have a twisted upper that I'm still debating whether or not to use for a .22 build (I got it mostly un-twisted).

A stripped upper made from a quality forging isn't very expensive, and it will let you avoid all sorts of headaches.

The suggestion for soldering originated from me in a response to the other recent thread on this.  You are correct, aluminum typically isn't soldered.  But given the options I said soldering was the *least* objectionable.  The joint would be weak, but probably not as weak as that created by welding or brazing on 7075. It was given in the context of a "discussion" where the OP asked how a joint could have been welded better, and to which one of my answers was "It shouldn't have been welded in the first place."

This is spot on.

I'll only add that welding 7000 series aluminum is like trying to cold MIG cast iron; there is very little strength to the joint.  Also, on ruining the temper; it's even worse than an untempered piece, as the temper will only be affected where the temperature was high enough to anneal, resulting in a piece with inconsistent temper, further promoting cracking.