CHS Steel Sign Posts vs Aluminium Sign Posts

Steel vs Aluminium Sign Posts (Galvanised Steel vs 6005A‑T6 Aluminium)

Why this comparison matters

In the sign industry, sign posts can feel like a “commodity”: you pick a diameter, choose a finish, and get the job installed. The reality is that material choice affects almost everything that happens next — how easy the post is to handle on site, how it looks after a few winters, how it behaves if a vehicle hits it, and how well it stands up to wind loads.

This guide compares galvanised steel sign posts with aluminium sign posts made from alloy 6005A‑T6 (a higher-strength alloy than the more commonly used 6063‑T6). It explains the practical differences between the two materials in clear, plain language, while also covering the relevant standards and specifications that commonly apply to highway and commercial signage projects.

The short version (for buyers)

If you want a tough, traditional post with very high stiffness and a proven record on highways, galvanised steel is a safe choice — provided it is specified and finished correctly.

If you want easier handling, excellent corrosion resistance, cleaner aesthetics, and strong performance without the weight penalty — especially when using 6005A‑T6 rather than 6063‑T6 — aluminium often delivers a better whole-life outcome.

The best choice depends on where the sign is going, the wind loading, the risk of impact, the finish you need, and how much you value installation time and long-term maintenance.

Common sign post sizes (what most people actually use)

Most UK signage projects revolve around a small set of standard diameters:

50mm – small plates, estate and commercial signage, short installations
76mm – general signage, many single-post applications
89mm – the workhorse size for highway signs
102mm – larger signs and higher wind exposure
114mm – heavy-duty installations and large-format sign faces

It’s worth remembering that post size is not just about “strength”. It also affects passive safety classification, clip compatibility, foundation size, and (for steel in particular) handling effort.

Strength and stiffness: what people mean when they say “stronger”

Buyers often ask: “Which post is stronger?” but there are two different things going on:

Strength (how much stress the material can take before it permanently bends)
Stiffness (how much it flexes under load)

Steel generally wins on both, but that’s not the whole story — because aluminium’s lighter weight and corrosion behaviour can make it the better overall solution for many signs.

Aluminium: 6005A‑T6 vs the standard 6063‑T6

A big hidden factor in aluminium posts is the alloy. Two posts can both be described as “aluminium T6” and still behave very differently.

6063‑T6 is commonly used because it extrudes easily and gives a good surface finish.
6005A‑T6 is chosen for sign posts because it is roughly 30% stronger in yield strength terms, and offers improved rigidity.

In practical terms: if you’ve ever seen an aluminium post slowly “lean” over time on an exposed site, alloy choice is one of the reasons. A 6005A‑T6 post is more resistant to long-term bending, especially when supporting larger sign faces in higher wind areas.

If you’d like a deeper technical explanation of how these two alloys differ and why it matters for sign posts, see: 6005A vs 6063 Aluminium Alloy – What’s the Difference?

Steel: very stiff, very dependable — but heavier and coating-dependent

Steel sign posts are naturally stiff, which is a real advantage for larger signs. Less flex can mean the sign stays aligned, the fixings see less movement, and the structure feels “solid” even in gusty conditions.

The trade-off is weight and corrosion risk if the protective system is poorly specified or damaged.

Passive safety and industry standards: BS EN 12767 (Annex K)

When signs are installed near live carriageways, impact safety becomes a core requirement.

BS EN 12767 is the standard used for passively safe support structures for road equipment. Importantly, Annex K provides a commonly used route to compliance for standard posts without needing bespoke crash testing.

In simple terms, Annex K recognises that smaller, thinner-walled posts will naturally behave in a safer way during an impact. As a widely used rule of thumb:

Steel and aluminium posts with a diameter of 89mm or less
and a wall thickness of 3.2mm or less

are generally treated as passively safe when installed appropriately.

What this means for buyers is straightforward:

If your project needs passive safety, staying within the ≤89mm / ≤3.2mm envelope is a sensible and commonly specified path.
If you need 102mm or 114mm posts close to traffic, you may need additional design decisions (for example breakaway solutions, relocated siting, or engineered passive-safe systems).

This is one reason 89mm is so popular: it often provides a strong practical balance of rigidity and safety classification.

For a dedicated explanation of aluminium posts and impact performance, see: Are Aluminium Sign Posts Passively Safe?

Wind loading: when the post choice becomes obvious

Wind loading is where the difference between materials shows up quickly. A sign face is essentially a sail; the bigger the sign and the more exposed the site, the more force is transferred into the post and foundation.

When steel tends to make sense

Steel can feel like the easy answer when:

the sign is large
the site is exposed (coastal, hilltop, open road)
minimal flex is important
the project is cost-sensitive on material

Steel’s stiffness means you often get good performance without needing to increase diameter. For some large signs, steel can allow simpler designs (fewer posts or smaller diameters) compared with aluminium.

When aluminium 6005A‑T6 earns its keep

Aluminium comes into its own when you want strong wind performance but need to balance:

safer manual handling
quicker installation
long-term corrosion resistance
a cleaner, more consistent finish

Using 6005A‑T6 rather than 6063‑T6 matters most on larger signs and windy sites. The increased yield strength helps the post resist permanent bending and improves overall “rigidity feel” compared with standard aluminium posts.

A practical way to think about it:

If you’re choosing aluminium for a demanding site, alloy and wall thickness are not the place to cut corners.

Weight, logistics and installation: the everyday reality on site

This is often the deciding factor for installers. Aluminium is roughly one‑third the density of steel, which usually translates into major day-to-day benefits:

easier to carry and position
reduced manual-handling risk
faster installs (especially multiple-post jobs)
lower transport weight (more posts per vehicle, potentially lower cost)

Steel posts, especially in longer lengths and larger diameters, can become a two-person lift or require mechanical assistance. That might be fine on planned highway works, but it can slow down small commercial installs or reactive replacement jobs.

If you’re doing repeated installs, the labour time and fatigue add up — and that’s where aluminium can be a better “whole project” choice even if the material price is higher.

Finishes: what the customer sees — and what protects the post

Finishes aren’t only cosmetic. They’re also the frontline defence against weather, UV, road salt, and knocks.

Aluminium finishing options (appearance + durability)

Aluminium has a natural corrosion advantage: it forms a protective oxide layer on its own. That means finishes are often chosen for aesthetics, extra durability, or brand consistency, rather than because the post would otherwise fail.

Common aluminium finishes include:

Mill / raw finish – the as-extruded surface. Practical and cost-effective, but it can show die lines and may carry a light residue from production.
Powder coating – the most common finish in the sign industry. Tough, colour-stable, and available in standard and custom RAL colours.
Anodising – creates a hard oxide layer integrated into the metal. Gives a premium metallic look and excellent weathering performance.
Wood effect finishing – a decorative option that gives timber appearance with aluminium durability.

Steel finishing options (protection first, looks second)

Steel needs protection. The baseline for outdoor steel sign posts is hot-dip galvanising. This creates a zinc coating that acts as a barrier and also provides sacrificial protection if scratched.

Steel finish options typically include:

Galvanised (hot-dip) – the standard highway look. Very durable, but visually industrial.
Powder coated over galvanising – improves aesthetics and adds another protective layer.
PVC coated – a plastic outer layer. It can look neat at first, but it has a known risk: if PVC cracks or splits, moisture can get underneath and rust can spread unseen.

If you’ve ever seen a green PVC-coated post that looks fine at a distance but is rusting aggressively beneath, that’s the mechanism.

Corrosion and long-term maintenance: what fails first

In real-world UK conditions, corrosion issues often determine whether a post lasts 10 years or 30.

Aluminium: predictable and low-maintenance

Aluminium does not rust in the way steel does. Scratches don’t lead to spreading structural corrosion. That’s why aluminium is popular for:

coastal sites
areas treated with road salt
locations where maintenance access is difficult
commercial installs where appearance matters long term

Steel: excellent when galvanised properly — but vulnerable if coatings are compromised

Galvanising is very effective, but steel remains a coating-dependent system. Problems usually start where:

posts are struck or scraped (vehicles, bins, maintenance equipment)
PVC or paint is damaged and water is trapped
the post base sits in waterlogged ground

For UK highways work, it’s common to specify galvanising to BS EN ISO 1461. Buyers should check that this is explicitly stated and supplied, not assumed.

Recyclability and sustainability

Both materials are recyclable, but aluminium has a particularly strong story in signage.

Aluminium is 100% recyclable with no loss of properties and has a strong scrap value, which encourages recovery.
Steel is also widely recycled, but it is heavier to transport and handle.

From a practical sustainability angle, aluminium often wins on whole-life impact because it is lightweight to transport, corrosion-resistant (so less repainting/maintenance), and easy to recycle.

How to choose: a practical decision guide

If you’re buying sign posts, the “best” option depends on the job. Here are common, real-world decision points.

Choose galvanised steel when…

the sign is very large and stiffness is the priority
you want a traditional highway specification approach
the site is extremely exposed and you want maximum rigidity
handling and transport weight are less of a concern

You can view the available range of circular hollow section steel posts here: Galvanised Steel Sign Posts (CHS)

Choose aluminium 6005A‑T6 when…

installation speed and manual handling matter
corrosion resistance is critical (coastal, salt, wet environments)
you want a smoother, more consistent finish
you want strong wind performance without the weight
you want a long life with minimal maintenance

You can explore aluminium post sizes, wall thicknesses and finishes here: Aluminium Sign Posts

Avoid common mistakes

Assuming all aluminium posts are equivalent (they aren’t — 6005A‑T6 vs 6063‑T6 matters)
Choosing PVC-coated steel for harsh environments without considering cracking and trapped moisture
Oversizing posts near traffic without considering passive safety requirements (especially above 89mm)

Comparison table (quick reference)

Category	Aluminium Sign Posts (6005A‑T6)	Galvanised Steel Sign Posts
Strength (material)	High for aluminium; improved vs standard 6063	Very high
Stiffness (flex)	More flex than steel; alloy helps	Very stiff
Weight	Very light; easier handling	Heavy; slower handling
Corrosion	Excellent; no rust	Depends on galvanising and coatings
Finishes	Mill, powder coat, anodised, wood effect	Galvanised, powder coated, PVC coated
Passive safety route	Often straightforward at ≤89mm / ≤3.2mm	Often straightforward at ≤89mm / ≤3.2mm
Best use cases	High corrosion sites, fast installs, aesthetic projects	Very large signs, maximum rigidity, traditional highway specs

Final thoughts

Steel and aluminium sign posts both have a place in modern signage. If you need maximum stiffness for a very large sign and you are working to established highway-style specifications, galvanised steel remains a dependable option — as long as the galvanising and finishing system is specified properly.

If you want a post that installs faster, is easier to handle, resists corrosion for decades, and looks cleaner long-term, aluminium is usually the better choice — and if you want aluminium that performs confidently on larger signs and exposed sites, choosing 6005A‑T6 rather than standard 6063‑T6 is a meaningful upgrade.

For a broader overview of post materials and typical applications, you may also find this useful: Types of Sign Posts – Comparing Materials and Applications.