Cast aluminum-nickel bronze (pics!)

[StevenRS11]

Hey! So, I've recently been playing around with different bronzes to cast bells in. Considering how expensive tin is, I thought the high alloy aluminum bronzes might work. Well, they don't- too hard to cast.

That said, they are incredibly strong alloys, so I decided to see if I could cast a simple knife and actually get a cutting edge on it.

All things considered, I'm rather pleased. It's a bit rough, but that's just more room to improve, right?

In terms of the metal itself, it's pretty close to C95500. 10.5% Al, 5% iron, 4% nickel and 3% manganese with balance copper. As cast, it's nearly impossible to file and after heat treatment the file doesn't even touch it. I peened the edge to harden it further, and I'll get back with some cutting tests later!

I feel like it would make a good metal for a dive knife or something. Anyone worked with these bronzes before? They seem more than comparable to many of the stainless steels used in knives currently, except they have even better corrosion resistance. Gotta love self healing sapphire coatings!

 

[Stacy E. Apelt - Bladesmith]

I have made a few bronze daggers and period pieces. It worked for a few millennia, so there is nothing wrong with it. Edge holding is an issue when compared to steel.

IIRC, bronze is a bit more brittle than a hard use knife wants.

Work on your casting quality, and use plenty of flux to clean off the molten bronze when casting. Make a larger bar and machine/file/forge it to the final shape. This removes most of the surface flaws and inclusions. Casting temperature control is also an issue with getting voids and pitting.

 

[StevenRS11]

Huh, pictures broke. Fixed them. In that picture, the knife is just stuck in there, not permanently mounted. I think I will use some black epoxy to mount it and fill the gaps. Should look decent sanded down.

Yea, I need to work on the casting setup for this alloy. Its not particularly fluid, has massive shrinkage, and develops a rather tenacious aluminum oxide dross layer. Its also tricky to flux- I cant use any boron bases fluxes because they react with the aluminum, and it's too hot for chlorides. I need to get some fluoride based salts and try those.

As for performance, it seems to work pretty well. It's actually harder than the cheap SS kitchen knives I have, and it hones to an absolutely razor sharp edge on a polished length of hardened drill rod. Are their any decently objective tests for edge durability/etc that I can use? I am running out of hair on my arms.

I hope this class of bronzes may work better than the traditional tin bronzes because they have significantly higher yield strengths and better elongation. What determines edge holding ability anyway? I bet that's a science all by itself.

 

[Bill DeShivs]

If your file is skating off bronze, you need a new file!

 

[StevenRS11]

If your file is skating off bronze, you need a new file!

Honestly, 'new' might be the problem. All I've seen for sale are cheap overseas crap that half the time aren't even ground right. It hardly would sharpen my old axe the day I bought it. Anyone know where to get decent files?

Also, the file did mark the bronze, it just wouldn't bite at all. It felt like filing spring temper 1085.

I went ahead and epoxied it in the antler, added a picture of the finished product to the op. Now I'm using to carve the next one out of foam, heh. I mangaged to get some fluoride based flux, so hopefully I'll have a better melt.

 

[Stacy E. Apelt - Bladesmith]

I agree with Bill. Bronze may get hard, but it will still be in the upper Rc 40's. It should file. It may be tough, and difficult to file, but not as hard as hardened steel.