Air carrier Captain reported two hard over events when connecting Autopilot A. Flight crew disconnected autopilot and hand flew aircraft back to departure airport.

Narrative

Turning right into the sun out of 5000ft; eyes started to water; with aircraft trimmed; I selected autopilot A. Immediate; abrupt; right hard over exceeding autopilot parameters and it disconnected. Hand flew aircraft to 12;000 checking trim; overhead; assessing for any obvious issues. Nothing unusual was noted. I ensured aircraft was in trim; while flying wings level in a climb; and selected autopilot A again. Repeat of previous abrupt/violent hard over to the right; exceeding autopilot parameters; with resulting autopilot disconnect. Ran the checklist for uncommanded autopilot disconnect. Elected to return to the airport as it was an extreme autopilot disconnect. Ran non-routine landing checklist. Burned down fuel to max landing as the aircraft was flying as expected and without issue by hand. Landing uneventful. Cause - Startle effect is real. I missed the 'my aircraft' call getting the aircraft under control the first time. (I'm not sure if flight recorders are checked; but there was likely some expletives in place of the 'my aircraft' call; I apologize.) My First Officer (FO) did say 'your aircraft.' When we ran the checklist for uncommanded autopilot disconnect; it did not say to select the other autopilot; although we discussed it; and decided the airplane was flying fine manually; and the disconnect on A was extreme enough that we didn't want to experience issues with B. That said; the first thing maintenance asked; was if we tried B. Suggest revising the checklist if they want the crews to try the other autopilot regardless of a hard over.Suggestions - Mechanical failures happen no matter how good a maintenance program. I don't see how this could have been prevented.