Brand of the Sun

The metal of a dagger or sword you are holding is imbued with the Sun's power.
For the duration, you can use your spellcasting ability instead of Strength for the attack
and damage rolls of melee attacks using that weapon, and the weapon's damage die becomes one d- higher. (d4 becomes d6, etc.) 
The weapon also becomes magical, if it isn't already.
The spell ends if you cast it again or if you let go of the weapon.