Melting point of boron is much higher than aluminium why
Answers
Those are two pretty strange elements to be comparing. Is this actually a homework question? Or is in a general interest question? Either way it seems a tad odd.
I can't really give you a decent answer. Hopefully someone else will for both our sakes, but I'll answer in case no one else has time to.
All I can say is intermolecular forces. That's essentially the only factor that affects melting or boiling point (at the same temperature and pressure).
Elemental boron has a giant covalent structure much like diamond. Boron nitride is isoelectronic with carbon so you can get diamond and graphite like structures. It obviously won't be the same for trivalent boron and I can't quite picture it (given that 3 coordinate boron is normally planar).
Silicon also has a giant covalent structure just like carbon. The difference is that B-B bonds tend to be a lot stronger than Si-Si bonds. Stronger bonds mean more energy to break which means higher melting point.
Hopefully someone will tidy up this answer!