Complex sentence: 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.
Split into simpler sentences: 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.