Anyone familiar with aluminum?

[olmeri]

I am interested in buying aluminum tubes to be used as standing slats in a deck railing. These will be outdoors and exposed to rain at times. Is anodizing necessary or will a natural oxide layer form over time? I don't mind if the surface becomes a bit mottled/grayish like a lamppost, but if the surface becomes grainy, pitted, and unevenly discolored, I'm very hesitant. Does anyone have personal experiences with this or have pictures of how non-anodized aluminum looks after a few years in the rain?

 

[Gabbe1]

As long as there are no salts or other chemicals in the rain, I don't think aluminum corrodes. It might also depend on what alloy it is, but generally it should withstand regular water.

 

[MB77]

Aluminum that is not treated will corrode, we in the industry call it "white rust" and it is almost impossible to remove without processing/polishing.

Untreated aluminum left outdoors for an extended period does not look good, it becomes white mottled as mentioned.

The belief that untreated aluminum does not corrode is a misconception that many people have.

 

[Drosen]

I correct the spelling to corrode.

 

[mexitegel]

As mentioned, you need to treat it for it to work, if you want the same surface as a lamppost, then it's hot-dip galvanized steel.

 

[Thomas_Blekinge]

There are many different aluminum alloys with completely different properties. Pure aluminum forms a protective oxide layer that resists further corrosion. Other alloys are extremely resistant in all environments, for example, marine aluminum.

The following table provides an overview:
Table 1. Aluminum alloys and their applications
Alloy series Alloy elements Properties Applications
1XXX None (>99% Al) Good weldability, good corrosion resistance Conductors, food industry, deep drawing
2XXX Copper High strength, poor weldability, good machinability Air frames, Aircraft parts, rivets, machinery components
3XXX Manganese Good weldability, good corrosion resistance Marine structures, building industry, radiators, tubes/pipes, soft drink cans
4XXX Silicon Welding material
5XXX Magnesium
Good weldability,
Good corrosion resistance Chemical plants, marine structures, shipbuilding
6XXX Magnesium
Silicon Good weldability, good corrosion resistance Extruded profiles, window frames, sailing boat masts, diversified constructions
7XXX Zinc
High strength Bridges, beer barrels, aircraft, space industry, ski poles

Unfortunately, the formatting went haywire.

What kills all aluminum is galvanic corrosion when aluminum is in contact with other metals (iron, steel, stainless, brass) under moisture.

I assume you're building the rest of the railing with pressure-treated wood that contains a lot of nasty and toxic heavy metal salts. This is a mistake most people make. Then you should not use aluminum.

 

[olmeri]

Aluminum that is not treated will corrode, we in the industry call it "white rust" and it is almost impossible to remove without processing/polishing.

Untreated aluminum that is left outdoors for a long time does not look good, as mentioned it becomes white-streaked.

The belief that untreated aluminum does not corrode is a misconception many hold.

One is taught that aluminum oxidizes and that this oxide layer (unlike iron rust) forms a protective film. That's what is done with anodizing, though the oxide layer becomes thicker.

This white rust is something that continues to develop and not something that occurs when the oxide layer forms?

 

[ion]

Cheaper alternatives are iron pipes painted with Hammerite, http://www.hammerite.se/metaltype-specific/aluminium,stal/

 

[olmeri]

There are very many different aluminum alloys with completely different properties. Pure aluminum forms a protective oxide layer that resists further corrosion. Other alloys are extremely resistant in all environments, e.g., marine aluminum.

The following table provides some overview:
lications.
Table 1. Aluminum alloys and their applications
Alloy series Alloy elements Properties Applications
1XXX None (>99% Al) Good weldability, good corrosion resistance Conductors, food industry, deep drawing
2XXX Copper High strength, poor weldability, good machinability Air frames Aircraft parts, rivets, machinery components
3XXX Manganese Good weldability, good corrosion resistance Marine structures, building industry, radiators, tubes/pipes, soft drink cans
4XXX Silicon Welding material
5XXX Magnesium
Good weldability,
Good corrosion resistance Chemical plants, marine structures, shipbuilding
6XXX Magnesium
Silicon Good weldability, good corrosion resistance Extruded profiles, window frames, sailing boat masts, diversified constructions
7XXX Zinc
High strength Bridges, beer barrels, aircraft, space industry, ski poles

Unfortunately, the formatting went awry.

What kills all aluminum is galvanic corrosion when aluminum is in contact with other metals (iron, steel, stainless, brass) under moisture.

I assume you are building the rest of the railing with pressure-treated wood containing lots of nasty and toxic heavy metal salts. This is a mistake most people make. In that case, you shouldn't use aluminum.

6060 is the one most people peddle. Then it should work without anodizing, right? Do you mean that against pressure-treated wood you can't use aluminum at all, regardless of whether it is anodized or not? It should be possible to solve this with plastic plugs where aluminum meets/goes into wood?

 

[ion]

A link to read, http://www.alumeco.se/Files/Billede...tomhus användning av obehandlat aluminium.pdf
Sure, it's a fantastic material. But for some things, I prefer iron, it offers many more possibilities, unless you are an expert at welding aluminum, then it's almost the same.