In some cases, the negative potential of magnesium can be a disadvantage: if the potential of the protected metal becomes too negative, hydrogen ions may be evolved on the cathode surface leading to hydrogen embrittlement or to disbonding of the coating.
The negative potential of magnesium can be a disadvantage. This is in some cases. Hydrogen ions may be evolved on the cathode surface. This cathode surface is leading to hydrogen embrittlement or to disbonding of the coating. The potential of the protected metal becomes too negative.