Somewhere around 17°F, it supercools to the point where an unopened can is still liquid, but as soon as the can is opened and the pressure is released, it almost instantaneously forms slush. This is actually my favorite way to drink Diet Coke because it's so much fun.
However, when you leave a 12-pack outside in the breezeway and forget it while the thermometer drops down to hover in the low single digits, It gets cold enough to freeze. There is a partial separation of the water from the syrup, and the dissolved carbon dioxide is released under tremendous pressure. The water freezes and expands, and it crowds the can and pushes out the safety dimples.
If you're lucky, you remember the 12-pack in time before the cans explode and bring the 12-pack inside and put it in the kitchen sink.
Unfortunately, there's this other bit where a gas under a lot of pressure in a tank actually increases in pressure as it warms up.
Sometimes to the point of making the cans explode. Really loudly.
And when you've forgotten about the whole thing and one of the cans explodes right next to you, it sounds an awful lot like a gunshot.
For all intents and purposes, it is best if this happens at a time when neither you nor any of your pets has to pee.