(a) Possibility -1 : One base material ( say metal A ) is more noble or cathodic than both weld metal (say W ) and other base metal (say metal B ) and weld metal W is more noble or cathodic than metal B - In this situation initially some galvanic corrosion will occur in W and B and A will have no corrosion. This may be possibly the case if we want to join Cu and Al with M51 where Cu (A) will be more cathodic to M51 weld (W) and Al (B) . So M51 weld and Al may corrode and Cu remains corrosion free.