No it won't.
Since Generation VI, flinch chances do not stack with items. Air Slash no longer gets a higher flinch rate because of King's Rock/Razor Claw, and neither do any other moves that already have a flinch chance. This includes Dark Pulse, Rock Slide, Iron Head and such.
Before this however, the flinch chances did stack, and the flinch chance by Razor Fang used to be 10%. So it followed this formula: flinch rate" + ("flinch rate"- 1)x .1
Since Air Slash's original flinch chance (before Serene Grace) is 30%,
Here's the expression: 30 + (30 - 1)x .1
= 30 + 29 x .1
= 30 + 2.9
And after factoring Serene Grace = 32.9 x 2
= 65.8% for a flinch.
Hope I helped!