#The Dark Lord using Avada Kedavra had never disarmed Harry.

While it is possible that the Dark Lord may have gained mastery of the Elder Wand if he’d disarmed Harry, that never happened. The Dark Lord had tried using Avada Kedavra on Harry with the Elder Wand twice, and it hadn’t caused Harry to be disarmed either of those times. The first time the Dark Lord tried to kill Harry with the Elder Wand, Harry meant to die, and let himself be killed.

> Voldemort had raised his wand. His head was still tilted to one side, like a curious child, wondering what would happen if he proceeded. Harry looked back into the red eyes, and wanted it to happen now, quickly, while he could still stand, before he lost control, before he betrayed fear –

> He saw the mouth move and a flash of green light, and everything was gone. <br><sub><sup>*- Harry Potter and the Deathly Hallows, Chapter 34 (The Forest Again)*</sub></sup> 

Harry hadn’t been disarmed as a result of that, since he still had his wand on him when he got up.

> Harry did not dare open his eyes, but allowed his other senses to explore his predicament. He knew that his wand was still stowed beneath his robes because he could feel it pressed between his chest and the ground. <br><sub><sup>*- Harry Potter and the Deathly Hallows, Chapter 36 (The Flaw in the Plan)*</sub></sup>

The second time the Dark Lord tried using the Elder Wand to kill Harry, Harry casts *Expelliarmus*, and the Dark Lord himself is disarmed, as well as killed by his own Killing Curse rebounding.

> *‘Avada Kedavra!’*

> *‘Expelliarmus!’*

> The bang was like a cannon-blast and the golden flames that erupted between them, at the dead centre of the circle they had been treading, marked the point where the spells collided. Harry saw Voldemort’s green jet meet his own spell, saw the Elder Wand fly high, dark against the sunrise, spinning across the enchanted ceiling like the head of Nagini, spinning through the air towards the master it would not kill, who had come to take full possession of it at last. And Harry, with the unerring skill of the Seeker, caught the wand in his free hand as Voldemort fell backwards, arms splayed, the slit pupils of the scarlet eyes rolling upwards. <br><sub><sup>*- Harry Potter and the Deathly Hallows, Chapter 36 (The Flaw in the Plan)*</sub></sup>

The Dark Lord never disarmed Harry, so he couldn’t have mastered the Elder Wand that way.