Aluminum/Zinc alloy vs. straight aluminum?

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Nephron44

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What are the advantages and disadvantages of aluminum/zinc alloys vs. regular aluminum for knife handles?

I have seen review after review of various knives (and some firearms) that denounce the use of zinc/aluminum alloys dubbed as “pot metal” and raving reviews for knives made of straight aluminum.

The way I understand it, metallurgically, zinc alloys are easier and cheaper to cast and manufacture, and they are more durable, stronger, and more impact resistant than aluminum.

The only downside I can think of to zinc alloys is the heavier weight.

If zinc alloys are so much better on paper than aluminum, why are they frowned upon in the knife community?
 
I would think the frowning depends on where the country of the forming and metals came from....?
 
I could be completely wrong here, but I wonder if the main reason zinc alloy materials gets a bad rap is that they are usually cast, whereas billet aluminum, particularly with knives and other small parts, is usually milled/machined. It seems to me there would be much more precise control with regard to fitment, tolerances, and general appearance of quality workmanship with milled/machined aluminum, as opposed to cast materials.

Overall the differences in strength between the two may be negligible, when it comes to knives anyway, as most applications are realistically non, or at least minimally-load bearing, whereas we all like good looking, light weight stuff in our pockets. The ability of aluminum to be anodized for color/coating options may also be a factor that zinc alloy cannot provide as readily.

Perhaps manufacturing, with CAD involved in most machining processes might be more cost-effective with regard to quality control over thousands, tens of thousands, hundreds of thousands of cycles, as opposed to casting. I don’t know if zinc alloy is even machinable, or harder to machine if it is.

I dunno, I might be a metalhead, but I’m not a metallurgist. Just spitballing.
 
Centermass said:
I could be completely wrong here, but I wonder if the main reason zinc alloy materials gets a bad rap is that they are usually cast, whereas billet aluminum, particularly with knives and other small parts, is usually milled/machined. It seems to me there would be much more precise control with regard to fitment, tolerances, and general appearance of quality workmanship with milled/machined aluminum, as opposed to cast materials.

Overall the differences in strength between the two may be negligible, when it comes to knives anyway, as most applications are realistically non, or at least minimally-load bearing, whereas we all like good looking, light weight stuff in our pockets. The ability of aluminum to be anodized for color/coating options may also be a factor that zinc alloy cannot provide as readily.

Perhaps manufacturing, with CAD involved in most machining processes might be more cost-effective with regard to quality control over thousands, tens of thousands, hundreds of thousands of cycles, as opposed to casting. I don’t know if zinc alloy is even machinable, or harder to machine if it is.

I dunno, I might be a metalhead, but I’m not a metallurgist. Just spitballing.
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Those all are valid points.

What sparked my question was I recently got a Cobratec that supposedly has an “aluminum alloy” handle, and is much heavier than my Benchmade/HK with straight aluminum, while being a smaller knife. I looked into it and found all this information about zinc vs. aluminum.

I agree the finishing between the handle scales is lacking, but for me, durability is more important than aesthetics, as long as there isn’t something grossly obvious.

The biggest place I see these gripes is when talking about Walther .22 firearms that use a zinc/aluminum alloy for the slides. I have had a few, and never had an issue, and the finish was spot on. People still complain all over the internet about Walther’s use of “pot metal” and I can’t figure out why.
 
Nobody uses "straight aluminum" for knife parts. Pure aluminum is nearly useless for structural parts. Aluminum alloys like 6061 or 7075 (itself an aluminum-zinc alloy) are commonly used.

You would be adding substantial weight by using zinc-aluminum alloys like ZA8/ZA12/ZA27, and would end up with worse properties. Plus, you're going to want to machine the castings to get precision fits on a knife handle anyway.
 
Nephron44 said:
Those all are valid points.

What sparked my question was I recently got a Cobratec that supposedly has an “aluminum alloy” handle, and is much heavier than my Benchmade/HK with straight aluminum, while being a smaller knife. I looked into it and found all this information about zinc vs. aluminum.

I agree the finishing between the handle scales is lacking, but for me, durability is more important than aesthetics, as long as there isn’t something grossly obvious.

The biggest place I see these gripes is when talking about Walther .22 firearms that use a zinc/aluminum alloy for the slides. I have had a few, and never had an issue, and the finish was spot on. People still complain all over the internet about Walther’s use of “pot metal” and I can’t figure out why.
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Your cobratech almost certainly uses cast parts with some zinc alloy. It is denser than most aluminum alloys while having worse mechanical properties.

This is why people don't like the Walther P22 having a cast slide. It is a cheaper material and inferior to a machined aluminum or steel part. They are notorious for cracking slides.
 
marrenmiller said:
Nobody uses "straight aluminum" for knife parts. Pure aluminum is nearly useless for structural parts. Aluminum alloys like 6061 or 7075 (itself an aluminum-zinc alloy) are commonly used.

You would be adding substantial weight by using zinc-aluminum alloys like ZA8/ZA12/ZA27, and would end up with worse properties. Plus, you're going to want to machine the castings to get precision fits on a knife handle anyway.
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Can you elaborate on the “worse properties?” Which properties? Exactly how much worse?

After scratching off a bit of finish on both knives, I can’t tell the difference in materials between my Benchmade/HK and my Cobratec, apart from the obvious weight difference. I’m guessing the Cobratec is made of one of the latter alloys you mentioned.
 
marrenmiller said:
Your cobratech almost certainly uses cast parts with some zinc alloy. It is denser than most aluminum alloys while having worse mechanical properties.

This is why people don't like the Walther P22 having a cast slide. It is a cheaper material and inferior to a machined aluminum or steel part. They are notorious for cracking slides.
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I’m sure it does, which I kind of knew when purchasing…well, at least I knew it was a lower quality than my Benchmades.

Can you elaborate on the worse mechanical properties? What exactly suffers? My biggest concern would be screws not holding, but so far they have been solid.
 
Nephron44 said:
Can you elaborate on the “worse properties?” Which properties? Exactly how much worse?

After scratching off a bit of finish on both knives, I can’t tell the difference in materials between my Benchmade/HK and my Cobratec, apart from the obvious weight difference. I’m guessing the Cobratec is made of one of the latter alloys you mentioned.
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As a quick example, something like ZA12 is about twice as dense as 6061/7075, and is generally slightly less strong than 6061 and substantially less so than 7075 (nearly half). Stiffness and hardness are relatively similar between the materials.

You're getting equivalent or worse mechanical properties, at least as far as knife handles are concerned, for substantially more weight. I'd argue that's a bad trade.
 
Problems occur during Anodizing with the Zinc added. During the anodizing process the part is Anodic ( positive) Aluminum oxide is brought to the surface creating the anodized surface. Zinc is an impurity that not only makes it more difficult during the etching process prior to anodizing in the way of heavy smutting, it also creates a porous surface. Usually any colored Anodizing is a sulfuric acid anodize( clear) followed by a dying process to give it the color of choice. After anodizing and dying there is a sealing process to close the pores to retain the dye. Not trying to be long winded, I am an electro player by trade , 42 yrs now. Thanks for listening,Troy
 
pholder said:
Problems occur during Anodizing with the Zinc added. During the anodizing process the part is Anodic ( positive) Aluminum oxide is brought to the surface creating the anodized surface. Zinc is an impurity that not only makes it more difficult during the etching process prior to anodizing in the way of heavy smutting, it also creates a porous surface. Usually any colored Anodizing is a sulfuric acid anodize( clear) followed by a dying process to give it the color of choice. After anodizing and dying there is a sealing process to close the pores to retain the dye. Not trying to be long winded, I am an electro player by trade , 42 yrs now. Thanks for listening,Troy
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🤣 Electro plater
 
The Zamak 3 alloys (96%Zn-4%Al) are used for die casting metal parts. They have poor corrosion and abrasion resistance so they need a thick protective coating (usually Copper, Nickel, and Chrome). Many automobile trim parts used to be made out of them. Hood ornaments, door handles, head and tail light bezels, nameplates, trim pieces, lock escutcheon plates, etc. Exterior parts needed roughly 1.5 mils of plating thickness to protect them from the elements. Zinc is so cheap that they are making pennies out it and then Copper plating them.
 
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Granted, the Zamak in these "quality" firearms often replaces steel rather than aluminum. The use of zinc in knives is pretty much exclusively with handles, but the die casting will nearly always result in a lower-spec product than machined aluminum, if only because the choice to use cast Zamak rather than machining aluminum means the manufacturer is already cutting costs and corners.

I'd add that calling Zamak an "aluminum/zinc alloy", if that's what whichever POS knife company in question is doing, is being somewhat deceitful and disingenuous. It's a zinc/aluminum alloy. Calling it an aluminum/zinc alloy implies that the major ingredient is aluminum when in reality it's a small amount.
 
Nephron44 said:
What are the advantages and disadvantages of aluminum/zinc alloys vs. regular aluminum for knife handles?

I have seen review after review of various knives (and some firearms) that denounce the use of zinc/aluminum alloys dubbed as “pot metal” and raving reviews for knives made of straight aluminum.

The way I understand it, metallurgically, zinc alloys are easier and cheaper to cast and manufacture, and they are more durable, stronger, and more impact resistant than aluminum.

The only downside I can think of to zinc alloys is the heavier weight.

If zinc alloys are so much better on paper than aluminum, why are they frowned upon in the knife community?
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You'll have to be more specific. Many aluminum alloys contain zinc. Many don't.

>>The most common aluminum alloy used for knife handles is likely 6061. Sometimes used in aerospace. I've seen it called "aerospace aluminum". It's not completely incorrect.
>>The most common aluminum alloy containing zinc I can think of off hand is 7075. Commonly used in Aerospace for primary structure.

6061 has better corrosion resistance. Less expensive. Easier to machine.
7075 has roughly twice the tensile strength of 6061.

For a knife handle, I'd likely choose 6061. Knife handles don't really require high tensile strength alloy. By the time you have enough volume of alloy to make a handle, 6061 will provide more than sufficient strength. And the other properties of 6061 also make it more desirable.
 
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