Anodising specification for solar mounting structures
Solar mounting structures are one of the few applications where anodising is not a choice. The specification says a minimum coating thickness — commonly 15 microns and often more — against a service expectation of 25 years, on structures that must carry wind loads to 2,400 Pa and mechanical loads to 5,400 Pa under IEC 61730.
The commercial difficulty is the gap between those two facts: the project is won on price, and warranted for a quarter of a century. Five years later, on a coastal site, the difference between a compliant coating and a nearly compliant one becomes a warranty claim.
What the specification actually asks for
Mounting rails and module frames are typically 6063-T5, chosen for extrudability and adequate strength rather than for corrosion behaviour. The anodic coating does the corrosion work.
A specification calling for "15 micron anodising" is asking for three things, only one of which most purchasers verify:
- Thickness, which is measurable and usually checked.
- Uniformity, which is rarely checked and is where thin spots hide.
- Seal quality, which is almost never checked in India and matters more than the other two combined for long-term coastal performance.
Why sealing decides coastal life
An anodic coating is porous as formed. Those pores run perpendicular to the surface and, left open, they are a direct path for chloride to reach the aluminium beneath. Sealing hydrates the oxide and closes them.
An unsealed or under-sealed 20 micron coating will underperform a properly sealed 15 micron one on a salt-exposed site. Thickness is the number on the purchase order; sealing is the property that determines whether the structure survives. And sealing contact time is the first thing shortened when a line is chasing throughput, which makes it the first thing to audit when field failures appear.
See sealing methods compared and nickel acetate sealing. The definitive test is admittance per ISO 2931 — the most sensitive sealing-quality check available, and one almost no Indian processor runs.
Where thickness goes wrong on a mounting rail
Inside channels and returns
Mounting rails are full of C-channels and internal returns. Current density falls sharply inside a recess, so the coating there can be half the thickness measured on the flat outer face — and the recess is where water sits.
At jig contact points
No coating grows where the jig touched. On a structure with a 25-year expectation, an uncoated contact patch on a salt-exposed surface is a corrosion initiation site.
Along the profile length
Current density varies down a 6-metre rail. Measuring the middle and passing the batch is how thin ends reach site.
At cut ends after fabrication
Cut, drilled or punched after anodising and the exposed aluminium has no protection at all. Fabrication sequence is part of the corrosion specification.
The measurement discipline that catches these is straightforward: multiple points including inside recesses and at both ends, not a single reading on a convenient flat face. See eddy current thickness measurement.
Specifying so you can enforce it
If you are buying anodised structures, a specification that can actually be held to account states:
- Minimum thickness and the measurement locations, explicitly including internal channel faces.
- Sealing verification method and acceptance criterion, not merely "sealed".
- Corrosion test evidence per ASTM B117, with duration matched to the site's exposure rather than a default.
- Fabrication sequence — anodise after cutting and drilling wherever possible, and a defined treatment for any surface cut afterwards.
- Alloy and temper confirmation per lot, since anodising response varies with chemistry.
If you are producing them, the same list is your qualification pack, and having it is the difference between competing on price and competing on evidence.
Doing it in house
Set the archetype to Long profile in our plant cost and payback calculator and enter your longest rail — solar rails commonly run 3–6 metres, so the line is cheaper than an architectural one at 6–7 metres.
For a structure maker currently outsourcing, use Captive mode with the rate your vendor charges today. The case here is often less about the rate saved and more about control: on a product warranted for 25 years, owning the process that determines whether it survives is worth something the spreadsheet does not show.
For the wider archetype, see anodising for extruded profiles.
Frequently asked questions
Specifications commonly call for a minimum of 15 microns on 6063-T5 rails and frames, and often more for coastal or high-exposure sites, against a 25-year service expectation. But thickness alone is insufficient: uniformity and sealing quality matter as much, and an unsealed 20 micron coating will underperform a properly sealed 15 micron one on a salt-exposed site.
Usually poor sealing rather than insufficient thickness. An anodic coating is porous as formed, and those pores are a direct path for chloride to reach the aluminium unless sealing closes them. Sealing contact time is also the first thing shortened when a line chases throughput, so it is the first thing to audit when field failures appear. The definitive check is admittance testing per ISO 2931, which almost no Indian processor runs.
At multiple points including inside C-channels and internal returns, at both ends of the profile, and away from jig contact marks. Current density falls sharply inside a recess, so coating there can be half what the flat outer face shows, and the recess is exactly where water collects. Measuring one convenient flat face in the middle is how thin sections reach site.
Before, wherever possible. Any surface cut, drilled or punched after anodising is bare aluminium with no protection at all, and on a coastal site that becomes a corrosion initiation point. Where post-anodising fabrication is unavoidable, the specification needs a defined treatment for the exposed surfaces.