India is building metro networks in more than 25 cities and localising coach manufacture, with domestic aluminium coach production targeted by FY27. Each metro coach uses roughly 6–8 tonnes of extruded aluminium, and a single 30-train line consumes around 1,500 tonnes. Much of that supply has historically been imported.

Operators specify that interior profiles be anodised or powder coated. That "or" is where suppliers lose money, because the two finishes fail differently on a surface the public touches thousands of times a day, and the qualification path is not the same.

What a coach interior actually demands

Rail interiors are an unusual duty. The profile is simultaneously a structural member, a visible surface, and something a standing passenger grips at speed. That produces four requirements that rarely appear together:

  • Abrasion resistance against continuous hand contact, luggage, and cleaning regimes that are far harsher than a building's.
  • Appearance stability over a service life measured in decades, not the five to seven years a commercial fit-out expects.
  • Cleanability without the finish degrading — including aggressive disinfectant cycles.
  • Fire, smoke and toxicity behaviour, which is where organic coatings carry an obligation that an anodic layer does not.

How the two finishes differ where it matters

Anodising

The coating is the substrate, converted. It cannot delaminate, because there is no interface to fail at. Hard, inorganic, contributes nothing to fire load, and wears rather than peels. Colour range is narrower and colour matching across production lots is genuinely difficult on long profiles.

Powder coating

An applied organic film with an adhesion interface — and an interface can fail. Far wider colour range and easier batch matching. Thicker, so it hides substrate imperfections. Carries fire, smoke and toxicity obligations that anodising does not, and chips rather than wears.

The practical distinction for a rail interior is failure mode. A worn anodic surface looks progressively duller. A failed powder coat chips, and a chip on a grab rail is both a visual defect and a maintenance liability. On a component replaced every few years that is tolerable; on one expected to last the life of the coach it is not.

Where powder still wins

Colour. If the operator's livery demands a specific shade across thousands of metres of profile from multiple production batches, powder will hold that match more easily than anodising will. This is a real constraint, not a preference — see anodising vs powder coating and the AAMA 2603/2604/2605 comparison.

The real barrier is qualification, not capacity

For an extruder or fabricator entering rail supply, the constraint is rarely tonnage. It is demonstrating a repeatable, documented process to a customer who will audit it.

What that means in practice

  • First-article approval against a written specification, with retained samples.
  • Documented process control — bath chemistry logs, thickness records per batch, sealing verification. Not a certificate, a system.
  • Traceability to alloy lot. This is where suppliers with recycled or mixed input struggle, because anodising response varies with alloy chemistry and the variation shows as colour drift.
  • Test evidence — thickness per eddy current measurement, corrosion per ASTM B117, and sealing quality, which is the test most often skipped in India.

A supplier with no anodising history is not disqualified by that history. They are disqualified by having no evidence system to show. That gap is closeable in months, and it is closeable before the plant exists.

Colour consistency along a six-metre profile

The problem that catches new entrants is not thickness. It is that current density varies along a long profile and between positions in the tank, and anodic colour follows current density. On a 6-metre coach profile, a variation invisible on a 2-metre component becomes a visible gradient — and adjacent profiles in a finished coach interior are compared side by side under even lighting by people with nothing else to look at.

Controlling it means cathode placement and area ratio, agitation that reaches the full profile length, jigging that presents every profile identically, and dye bath control if the finish is coloured. It is a plant design problem, decided before commissioning.

What the plant costs

Set the archetype to Long profile in our plant cost and payback calculator and enter your longest coach profile — typically 3–4 metres, shorter than architectural work and therefore a meaningfully cheaper line.

An extruder evaluating this as a captive investment should use Captive mode and put a figure on the unlocked market. For rail that term is the whole case: the outsourcing saved is modest, while qualifying for coach supply against a localisation deadline opens a market that is currently closed.

For the wider archetype, see anodising for extruded profiles.

Frequently asked questions

Should metro coach interior profiles be anodised or powder coated?

Operators typically permit either, so the decision turns on failure mode. Anodising is a converted layer of the substrate with no adhesion interface, so it wears progressively duller rather than chipping, and contributes nothing to fire load. Powder coating offers a far wider colour range and easier batch-to-batch matching, but has an interface that can fail and chips rather than wears. For a component expected to last the life of the coach and be gripped daily, anodising's failure mode is usually preferable; where a specific livery colour must be held across thousands of metres, powder is easier.

What is the main barrier to supplying anodised profiles for Indian rail?

Qualification, not capacity. A supplier needs first-article approval against a written specification, documented process control with bath chemistry and thickness records per batch, traceability to alloy lot, and test evidence for thickness, corrosion and sealing quality. Suppliers with no anodising history are not disqualified by that; they are disqualified by having no evidence system to show, and that gap can be closed before the plant exists.

Why is colour consistency harder on long profiles?

Anodic colour follows current density, and current density varies along a profile and between positions in the tank. A variation invisible on a two-metre component becomes a visible gradient on a six-metre one, and adjacent profiles in a finished coach interior are compared side by side under even lighting. Control comes from cathode placement and area ratio, agitation reaching the full length, and identical jigging — all plant design decisions made before commissioning.

How much aluminium does a metro coach use?

Roughly 6 to 8 tonnes of extruded aluminium per coach, so a single 30-train line consumes around 1,500 tonnes. With more than 25 Indian cities operating or building metro networks and coach manufacture being localised, the pipeline represents substantial demand that has largely been met by imports.