Aluminium

The aluminium alloys used in New Zealand for roof and wall cladding are included in the 5000 series.

• Aluminium 5005 has excellent workability, weldability, and corrosion resistance.
• Aluminium 5052 is a higher strength marine-grade alloy with exceptional resistance to corrosion in marine or industrial environments.

Following strain-hardening of aluminium alloys, tempering increases the ductility by low-temperature heating, and their description regarding hardness relates to the last number, e.g. H12 or H32.

The description of tempers given to aluminium alloys can be confusing because the different alloys are strain-hardened in different ways. As a result, different alloys with the same hardness description may have significantly different yield strengths.

Pure aluminium (99%) can be used as a soft edging for ridge or apron flashings required to act as a wind barrier.

Aluminium alloys are available in three surface finishes.

• Mill finish: A smooth, lustrous finish which will dull relatively quickly.
• Stucco finish: An embossed mill finish, which reduces the specular reflectance of a mill finish sheet.
• Painted finish: A range of painted finishes are available similar to those offered in painted steel.

The high reflectance and emissivity of unpainted aluminium can reduce heat transmission considerably.

Aluminium develops a thin oxide film on the surface that is impermeable to most airborne contaminants, except for strong alkalis and acids.