Stove element as a resistor
Do you have an ammeter to measure precisely how much current the tig welder outputs at its lowest 15A settings? 

Generally welding machines output current is not so well regulated in tight margins especially at such low settings. 

To answer your question, YES, you can use nichrome coil from stove heaters to get the current you want if you follow these steps.


Connect your 50A fullscale ammeter across the welder's output which is already set at its lowest current setting and mark the reading. Let say it reads 15A.
Now break the circuit and connect the anodizer to the welder and see how much current flows thru the anodizer. This current reading will definitely lower than 15A. Let say it now shows 10Amps.


Now you know that you need to dump 4Amps of current thru shunt the tig welder with some dummy resistance in order to get only 6Amp into the anodizer.


While keep observing the ammeter, connect the stove elements across the tig welder's output. Lower the resistance of the shunt to reduce the ammeter reading of the anodizer.


Adjust your resistance accordingly to get your desired current for proper anodizing process.