The Mythbusters were testing weather two semi trucks that collide at highway speeds into a car would turn the car into a pancake and fuse the semis trucks together. The were not able to prove either scenarios.
In usual Mythbusters fashion, they have to see what it will take to do what they were testing. To turn a car into a pancake, they went to New Mexico Tech to use their rocket rail to smash the car. There is a video of the results on YouTube.
They also fused sheets of metal together using explosives. If I can find that video I will add it.