From "The Avengers: Earth's Mightiest Heroes: Ultron Unlimited (#2.17)"
We have to get to Ultron!
Aye, the robotic demon has much to answer for!
[not even a dent
] My chassis is comprised of pure adamantium now, Avenger. It is unbreakable, even by your hammer.
] Well, if you don't mind, we'll keep trying!