Ralph wrote a nice answer for the Boeing 737, which is a conventionally controlled aircraft, meaning the yokes are mechanically linked to the flight control actuators.
The Airbus A320 however is a fly-by-wire controlled aircraft. This means that both sidestick input and autopilot commands are sent to flight control computers, which then calculate how to move the control surfaces to achieve the desired flight path:
(Airbus A320 FCOM - Flight Controls - Description)
While the autopilot will happily command inputs that would increase the angle of attack above its critical value, the flight control computers have built-in protections against this. These protections are active regardless of whether the pilots control the aircraft via the sidesticks or the autopilot controls the aircraft:
Control with autopilot engaged:
- The ELACs and SECs limit what the autopilot can order. [...]
- All protections of normal laws remain effective.
(Airbus A320 FCOM - Flight Controls - Normal Law)
In the case of increasing angle of attack, the following protection law would apply:
High angle of attack protection
Under normal law, when the angle of attack becomes greater than αprot,
the system switches elevator control from normal mode to a protection
mode, in which the angle of attack is proportional to sidestick
deflection. That is, in the αprot range, from αprot to αmax, the
sidestick commands α directly. However, the angle of attack will not
exceed αmax, even if the pilot gently pulls the sidestick all the way
back. If the pilot releases the sidestick, the angle of attack returns
to αprot and stays there.
This protection against stall and windshear has priority over all
other protections. The autopilot disconnects at αprot + 1°.
(Airbus A320 FCOM - Flight Controls - Normal Law)
Since the autopilot disconnects itself at αprot + 1°, it would not automatically recover from a stalled condition. However, AoA would reduce now anyway because the flight control computers would not allow any further elevator up actuation until AoA is below αmax again.
In addition to limiting the angle of attack via the elevator, the aircraft will also automatically set maximum thrust at some point. This is called Alpha-Floor protection:
Alpha-floor protection automatically sets the thrust at TOGA thrust,
when the aircraft reaches a very high angle of attack.
The Flight Augmentation Computer (FAC) generates the signal that
triggers the alpha-floor mode. This, in turn, sets TOGA thrust on the
engines, regardless of thrust lever position (Refer to 1.22.30 A/THR
The FAC sends this signal when the angle of attack is above a
predetermined threshold, that is a function of the configuration.
(Airbus A320 FCOM - Auto Flight - Flight Augmentation)
The accident you linked was in a Boeing 777, which is also fly-by-wire controlled and therefore also provides flight envelope protections. However, Boeing uses a somewhat different approach, where the protections increase the required force on the yoke to overcome them, rather than limiting what is being transmitted to the flight control actuators. This means, pilots can always overpower the envelope protections in a fly-by-wire Boeing.
The autopilot will however obey the flight envelope protections and therefore not stall the aircraft:
Flight Envelope Protection
There are three forms of flight envelope protection in the autopilot:
- stall protection
- overspeed protection
- roll envelope bank angle protection
An AUTOPILOT caution message and roll or pitch mode failures alert the
pilot if the envelope is exceeded, and the autopilot prevents further
(Boeing 777 FCOMv2 4.20.19 - Automatic Flight - System Description)
The stall protection will not allow the autopilot to trim the aircraft into a stalled condition and — similar to the Airbus Alpha-Floor protection — also use the autothrottle to increase airspeed:
Stall protection reduces the likelihood of inadvertently exceeding the
stall angle of attack by providing enhanced crew awareness of the
approach to a stall or to a stalled condition.
Stall protection limits the speed to which the airplane can be
trimmed. At approximately the minimum maneuvering speed, stall
protection limits the trim reference speed so that trim is inhibited
in the nose up direction. [...]
The autothrottle can support stall protection if armed and not
activated. If speed decreases to near stick shaker activation, the
autothrottle automatically activates in the appropriate mode (SPD or
THR REF) and advances the thrust to maintain minimum maneuvering speed
(approximately the top of the amber band) or the speed set in the mode
control panel speed window, whichever is greater. The EICAS message
AIRSPEED LOW is displayed.
(Boeing 777 FCOMv2 9.20.12 - Flight Controls - System Description)
In the accident flight, autothrottle inputs where obviously no longer available since both engines had already failed. This also has other implications (e.g. both engine generators fail, which requires emergency electrical power from battery or RAT), which can result in the loss of flight envelope protections:
Flight Control System Secondary Mode
When the PFCs can no longer support the normal mode due to internal
faults or lack of required information from other airplane systems,
they automatically revert to the secondary mode. [...]
The following functions are not available in the secondary mode:
- autopilot [...]
- envelope protection [...]
(Boeing 777 FCOMv2 9.20.7 - Flight Controls - System Description)