Airweight frame composition

[semperfi.45]

In reading the Gun Digest Book of S&W I find this...

"Aluminum is much lighter and softer than steel. What makes aluminum appear hard is anodizing. The hard coat anodizing we are all familiar with is a surface treatment, not a through hardening like heat treatment is. Once you either wear through the anodizing, or break it, the softer substrate will quickly peen or propogate the crack".

Is this true of the newer Airweight's or is the Airweight composed of an aluminum alloy that is hardened through? I ask because I recently cracked my 442-2 just forward of the thumb piece where the center pin rubs against the frame. S&W customer service came through for me and replaced it with a no lock 442.

 

[Alk8944]

That statement was not entirely true even when it was published. While pure Aluminum in not heat-treatable, neither is pure Iron.

From the beginning the most common Aluminum alloy used for firearms frames was alloy 6061, commonly referred to as "aircraft aluminum" since it is used in aircraft applications. This is both forgeable and heat-treatable to various degrees of hardness from T-1 to T-6, the hardest, and strongest. S&W also uses a Scandium-Aluminum alloy in current revolvers which are designated Sc for Scandium. The Scandium alloy is also heat-treatable.

Even the hardest heat-treatment, T-6, is still relatively soft, about the same as so-called "mild steel", compared to common gun steels. For this reason it is finish treated by a process nown as anodizing. This is literally an electrolytic process in which the Aluminum part becomes the Anode, hence the name. Anodizing does nothing more than accelerate the normal oxidation of the Aluminum creating a much thicker depth of Aluminum Oxide on the surface.

In chemical terms Aluminum Oxide is called Corundum. Corundum is second only to Diamond in hardness, and is aproximately the same hardness as the Tnngsten Carbide typically used for Carbide reloading dies. Diamond has a hardness of 10 Mohs, while Corundum and Tungsten Carbide are aproximately 9 Mohs.

The anodized surface, while hard, can be worn off of the base metal. The larger bearing surface the better. The center pin doesn't have much surface and will ear through the anodozing into the base metal.

 

[Spotteddog]

There are so called "modern" alloys that are "harder" through out. But most of what you read is essentially accurate and still applies. Think about Chevy Vega cylinder walls (aluminum) poor resistance to the piston rings (iron) and how often you saw them blowing oil. So, in areas that abrade or are subjected to excessive clearances you'll have trouble sooner with aluminum, than with steel.

 

[endgameAK]

My M396 Mountain Lite in .44
special has a frame made of 7075 T-7 ... has thrived thru 1000+ rounds, with no failures or dings The tempering scale doesn't end at T-6.

There are 3 different series of "aluminum aircraft" alloys, that I've used for various projects. 6000, 2000, and 7000. 6000 is the most common, the longest in service, and the weakest. 7000 series, the strongest, most durable, is used for the receivers of our M-16 series of rifles.

Don't lump all aluminum into the same category.

 

[Spotteddog]

Absolutely Endgame.
All I meant was that the base characteristics of the parent material are still present, regardless of improved metallurgy? And yes, there are tremendous examples of toughened up Aluminum! The difficult part sometimes, is trying to determine what material was in play at the OEM.

 

[wheelgun1958]

6000 series aluminum is also the only AL alloy that is weldable.

My M396 Mountain Lite in .44
special has a frame made of 7075 T-7 ... has thrived thru 1000+ rounds, with no failures or dings The tempering scale doesn't end at T-6.

If I recall correctly my structures (aviation) background, T6 is a temper designation from the factory while T7 is a temper as applied in a shop environment. They are essentially the same.

 

[endgameAK]

I believe that 5000 series (marine) Aluminum is also weldable.