Alloy and Temper
The four-digit system used for designating the alloys is an international one which has been adopted by all major aluminium producers. The first digit indicates the alloy group. The second digit indicates modifications of the original alloy or impurity limits. The last two digits identify the specific alloy and aluminium purity.
Alloys recommended for roofing and wall cladding products are 5052, 5005 and 5251. In particular, the magnesium and chromium content of 5052 makes this alloy appropriate for recommended use in marine environments, and this alloy is in common use in New Zealand for roofing and wall cladding products.
The temper designation describes the combination of cold working and heat treatment performed to give the material appropriate forming and end use mechanical properties. The tempers used for roofing and wall cladding products are H34 for crimp curving and folding, and H36 for rollforming.
These tempers involve strain-hardening and then low temperature heating to slightly lower the material strength and increase ductility
Working and Finishing
All aluminium alloys work harden and gain strength during forming operations. Thus the appropriate alloy and temper must be selected to allow the appropriate degree of formability, without excessive hardening and consequent splitting.
Mechanical fasteners, whether rivets or screws, are available in aluminium. Where the use of aluminium fasteners is plainly unsuitable, e.g. self-drilling screws, stainless steel is normally regarded as the best alternative.
With correct pretreatment procedures, aluminium is an excellent substrate for applied coatings. The pretreatment uses phosphate or chromate conversion coatings to chemically remove the aluminium oxide layer.