Arcane Weapon

Source: Unearthed Arcana 60 - The Artificer Returns
  1st-level transmutation
  Casting Time: 1 bonus action Range: Self Components: V, S Duration: Concentration, up to 1 hour
  You channel arcane energy into one simple or martial weapon you’re holding, and choose one damage type: acid, cold, fire, lightning, poison, or thunder. Until the spell ends, you deal an extra 1d6 damage of the chosen type to any target you hit with the weapon. If the weapon isn’t magical, it becomes a magic weapon for the spell’s duration.
  As a bonus action, you can change the damage type, choosing from the options above.
  At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, you can maintain your concentration on the spell for up to 8 hours.
  Spell Lists. Artificer