A general purpose aluminum rod will do just fine. I don't know what you're doing BUT get that sucker spotlessly clean first.. I'd run it through your parts washer then a couple cycles in your dishwasher. Then clean both the area and the rod with acetone just before welding.
I need to move some bolt holes. Will de-grease it and I have a good industrial ultrasonic cleaner. Will put it through several cycles. Just finished welding my oil pan and it got the pan nice and clean for welding.
I always clean with acetone as a final clean. I can tig weld just haven't done it in a couple years.
