Did I ruin my upper receiver?

[MWAG19919]

Long story short, I had my upper in the oven to cure Rustoleum high temp paint on the FSB. I'm adding a Centurion Arms C4 MLOK rail to my 14.5" SOCOM upper, and after cutting and shaving the FSB into a low profile GB, I needed to protect the metal. Their instructions say to bake at 250 for 30 minutes, cool for 30; bake at 400, cool for 30; bake at 600, cool for 30. All was well and the upper looked normal until I pulled it out after the 600 degree bake. It now has a rusted appearance. If it's just cosmetic that's fine, as I plan to Cerakote it anyway. But I'm afraid I might have weakened the receiver somehow by getting it hot. Am I okay, or is this landing me in the Gunsmithing Hall of Shame?

[url=https://flic.kr/p/2j2eaZM]

[sidewaysil80]

Why on earth didn’t you just put the fsb (or barrel) in their by itself :/

As far as your question I would guess finish, although 600 seems high

[Valhalla]

The color change is just from the finish; it is somewhat well known that baking black anodized surface will turn them into some kind of dark-brown color. But I do have concerns on the temperature... a quick Google search for "7075 annealing temperature" got me to this diagram:



Which would've suggested you may have significantly lowered the hardness of the upper... (600F = 315C)

Any metallurgist willing to chime in?

[Aetius]

Don’t know about you, but I would spend $70 and not have to worry about it

https://bravocompanyusa.com/bcm-uppe...emo-scratched/

[sidewaysil80]

Question, though...what happens if you out oil on the upper?

completely cosmetic/aesthetically speaking I’m wondering what oil does as it looks like a match to geissele ddc lol

[greene]

Burnt bronze for real on that one.

[MistWolf]

Annealing requires heating the alloy between 570°F to 770°F for thirty minutes to three hours, depending on the composition of the alloy and the size of the part. Temperatures for annealing 7075 are at the higher end. I'm certain you've partially annealed your upper, reducing hardening and strength. It can be heat treated to return it to full strength and worth doing for hands on learning.

From a practical standpoint, it's easier and more economical to replace the receiver. Chances are it's good enough to use until you can get a replacement.

[themonk]

Annealing requires heating the alloy between 570°F to 770°F for thirty minutes to three hours, depending on the composition of the alloy and the size of the part. Temperatures for annealing 7075 are at the higher end. I'm certain you've partially annealed your upper, reducing hardening and strength. It can be heat treated to return it to full strength and worth doing for hands on learning.

From a practical standpoint, it's easier and more economical to replace the receiver. Chances are it's good enough to use until you can get a replacement.

Exactly what I was going to say. I would add in the future and for other reading this thread to use Brownells aluma-hyde, duracoat, cerakote or even just krylon rattle can. None of those products get even close to that heat range.

[drewthebrave]

I work in the coating industry, and anodizing will discolor at high temp, but will not degrade until you get over 1000F. However, I'm not a metallurgist, so it's hard to say whether or not the aluminum was affected. Occasionally we'll see warping of aluminum sheets at temps above 600F, but most of that will depend on the quality of the aluminum. Thicker metal will take longer to warp or soften, and 7075 is probably the best case scenario for holding up at that temp.

How long was it at 600F? That's going to be the determining factor for whether or not your receiver is compromised... I think worst case scenario is that the receiver softened and could have warped out of true "center". Not a risk for catastrophic failure, but it may affect your zero or reduce precision. It could be fine, but you won't know for sure until you shoot it. If you see a major deterioration of accuracy, get a new receiver. If not, just call it a learning experience.

For future reference, I agree with the user above with a strong recommendation to only use coatings that cure at low temps (under 400F) like Duracoat, Alumahyde, Cerakote or even rattle can paint.

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[1_click_off]

You could al least show a pic of the FSB....