Yes you can cryo treat copper or any other metal. Treating the foil prior to folding would be best, you could also freeze again after folding or embossing the foil if you wanted but additional improvements will not be as significant compared to the first treatment. Heat treating the foil to soften the metal is worthwhile. The foil I used were heat treated first then I cryo treated them after embossing the foil with a zig zag fold. I hope this helps.
You need to figure out the alloy foil is made of and go check how to. Some alloys can not be neither tempered nor annealed. Whether or not 5um can be heated without oxidizing through is yet another question.
thank you for the answer. I almost got what I needed. i found the heating method doesn't work with the 0.4um copper foil that i have, because i tried it this morning, the copper foil is deformed, discolored and more fragile at 350 degrees celsius. maybe i will switch Use dry ice or liquid nitrogen to treat.
i tried heating with 0.4um copper foil branded as mont marte, it didn't work. perhaps the cryo method is more suitable. and I find this copper foil can't be folded at the moment because it's quite thin. I hope after cryo, I can fold it as I want.
I"m not quite sure what people think that cryo'ing copper would do. Unless there's a phase transition upon cooling (which there is for many types of steel - but NOT for copper), cooling simply slows down any change in microstructure. The kinetics are strongly exponential with temperature - if no beneficial changes happen for Cu alloys at room temperature, they certainly aren't going to happen when you cool it to cryo temps.
Many steel alloys undergo beneficial changes when cooled to cryo temps - but that is because of a martensitic phase transformation that occurs at low temperatures. Of course, this transformation isn't always a good thing - look at what happened to the liberty ships in the North Sea during WWII.
Rich