Galvanized metals contain zinc and is considered toxic, so why do people use this type of wire for housing breeding parrots?  I can't answer this question, but it has been used for years to keep birds in.  When building aviary cages or flights it needs to be washed and scrub to knock off any loose metal particles  so the bird can not ingest any loose particles. 

Galvanizing is a process to coat wire or metal to prevent  metals from rusting.  It is used as it's  probably the cheapest form of coating.  You absolutely could not afford wire if it could be  powder coated.  It would be so outrageously  priced that no one could afford it.  Galvanizing is mainly used for outdoor products.  Painted wire does not last at all outdoors.

We use this type of galvanized wire which is considered Galvanized After Welded (GAW). Pictured top left is rolled wire and comes in a variety of gauges and mesh sizes, we use 10 gauge being that it is good for most all Macaw size parrots. It is a fact that a Macaw can break the weld on the 10 gauge wire if they really wanted to, I have never had any problem with it.  The 8 gauge should be used with Hyacinth Macaws.  The smaller the gauge number, wire is larger.

Picture top right is the 12 gauge wire and is a good size for other parrot sizes. 

Picture on left is the 10 gauge wire and using 1 inch galvanized square stock, we have welded it to make a gate that is on the back door of the garage to keep the little dogs in the backyard when we want to keep the main door open to let air flow through the garage.
Picture on right is chain link fence which is also a galvanized product and is standard 11 gauge wire. Some people do use this for large Macaws. We do not use chain link for our birds as I feel it is too large for other critters to get in such as rabbits and squirrels.