Check your current system for electrolysis.

Should be less than .3 volt or 300 mV.

70blackfish went through this with two aluminum radiators in 6 months.

70blackfish already checked and added grounds from the radiator, motor, and every other component in his truck.

In your case you may have a bad ground or need to add grounds.

70blackfish cured his situation when he ran some Justice Brothers Radiator Cleaner (RC/3p)though the system. Then ran reverse osmosis water with Justice Brother Super Radiator Cooler (RC/22p).

He'd previously used Water Wetter with his other failed radiators. IMHO, the Radiator Cleaner chemical helped him a lot in his ordeal.

He lives in So Cal so freezing isn't an issue. But same results can be had with 50/50 antifreeze in place of the reverse osmosis water.

Check you electrolysis with a digital voltmeter. Put ground to battery and dangle the positive side in the liquid in the radiator without touching any part of the radiator itself.

The reading below is 76.8 mV or .0768 volts.