Does gallium expand when frozen?

Question

Gallium at room temp is liquid Water expands when frozen.

If gallium is kept from expanding as it becomes solid at a real low temp what would happen?

Answer 1

Yes, gallium, like water, germanium and bismuth, expands on freezing. You'll have to apply pressure to keep liquid gallium from expanding as it freezes. In fact, initially, this pressure will keep it in a liquid state. However, as you keep lowering the temperature, the metal will solidify at last and, if the container is tough enough, will either exist as a solid mass under enormous compressive strain or break up into pieces to accommodate the strain.
That's what would happen to water / ice too !

Answer 2

No. Water is rather exceptional in this case. Most liquids contract when they freeze because their molecules become more closely bound as they transition from a (disordered) liquid state into the orderly crystal structure of a solid. Even without phase changes, matter generally contracts as it cools because their molecules don't bounce of each other as fast due to thermal motion.

All this assumes that the pressure stays the same. To reverse your question, if gallium is contained in a strong container that prevented it from expanding as it melted, it would still melt, but at a higher melting point, and its pressure would increase significantly when it did.