AZ Coatings

AZ coatings are zinc-aluminium alloy coatings with a majority of aluminium. AZ coating, marketed as Zincalume® steel, is an alloy of zinc and aluminium which is now the most commonly used coating in New Zealand for protecting steel roof and wall cladding.

AZ coating is applied in the same way as other coatings, but with a pot temperature at about 140˚C higher than galvanised coating, and it is rapidly cooled to provide a dual-phase microstructure.

The alloy consists of 50 to 60% aluminium, zinc, and a small addition of silicon. In New Zealand, the ratio is nominally 55:45. These percentage ratios are by mass; by volume, the percentage ratio changes to approximately 80% aluminium and 20% zinc. Volume is probably a more realistic measure of its nature.

The alloy coating thickness generally used for steel roof and wall cladding is 150 g/m² (AZ150). This coating is approximately the same thickness (0.04 mm) as Z275 zinc. AZ200 coatings are available as a substrate for organic coated products to be used in very severe environments.

An AZ coating protects steel both as a barrier and sacrificially, as the aluminium content provides a barrier, while the zinc content of the coating will sacrifice itself to protect the base steel.

The AZ coating is finer grained than zinc alone and has a silver matt hue with a lightly visible spangle. This finish has a relatively high level of initial reflectivity, which darkens over time.

A thin acrylic film is applied during manufacture in New Zealand. The acrylic film acts as a roll forming lubricant and minimises finger marking and surface discolouration.