Alloy Structure - AlZnSn

In an attempt to formulate a Nordic Gold alloy, I managed to fail forward and learn a decent amount about the issues I came across. Information first verified by failure, then learned through research after, is somehow more rewarding to my mind than just reading about it and not trying it. That being said, I had no intent to act imprudently. I simply learned all I understood I needed to know, and found out through trial that there were some assumed details left out. Those omissions that caused error were not terribly surprising when I looked into them. Evidently, if you are doing such things, there is a vague assumption that you have some experience and did not just decide to start at this phase.

The composition of Nordic Gold is 89% Copper, 5% Aluminum, 5% Zinc, 1% Tin. The first problem I ran into was when I added the Zinc in my first attempt. I knew that it had the lowest melting point, and I knew that the Copper melting point of 1,085ºC (1,984ºF) exceeded Zinc's evaporation temp of 907ºF (1663.6ºF). No one talked very much about it being an issue besides warning that some Zinc Oxide smoke would be released and very visible and must be avoided. What I did not see in the attempts of others, or warned anywhere was that the Zinc being added last (and in my case of available pellets) act like a bunch of fire crackers when it sublimated on contact. Not expecting that, you can see I jumped a bit. In the top middle of the photo, you can see a bunch of zinc pellets flying back when I jumped at my surprise popping.

The entire attempt was a failure overall, but a learning experience. The mold did not pour correctly either as air became trapped and a mixture of oxidation and porosity made the end result in to a nearly unrecognizable mess. However, it did turn out looking fairly golden. Some pieces even had an odd bluing to them.

This bar is a result without any sanding or polishing. Uneven cooling is evident.

So, for the follow-up attempt, I wanted to try to avoid the issue of losing the Zinc. My idea was to first alloy the Aluminum, Zinc, and Tin, then I would melt the copper and add that bar. The thought was that it would reduce the immediate contact surface area and allow more to stay under the flux protected from oxidation. Specific Heat - the amount of energy, measured in joules, needed to raise the temperature of 1 gram of a substance by 1 degree Celcius. Different substances have different specific heats. Latent Heat - (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process—usually a first-order phase transition, like melting or condensation.

Latent heat can be understood as hidden energy which is supplied or extracted to change the state of a substance without changing its temperature or pressure. This includes the latent heat of fusion (solid to liquid), the latent heat of vaporization (liquid to gas) and the latent heat of sublimation (solid to gas) https://en.wikipedia.org/wiki/Latent_heat

I looked into available information and found out very quickly that I did not have much chance tightly controlling the situation in my backyard. However, I did understand better that Zinc requires little energy for vaporization, so starting 179ºC above the melting point as a minimum, due to needing the copper melted, left few options to control Zinc loss (at least in my back yard). So, I pursued my idea to make an alloy bar first to add to the copper. I first melted the Aluminum, using a little table salt (NaCl) as flux and to lower the melting point. I then added the Tin, which melted quickly and lowered the melting point of the Aluminum further. I'm still not comprehending how that works. Then, I added the Zinc after backing the temp down a little bit. I then poured it into a bar.

Left Aluminum Bar ---- Right 50% Aluminum, 25% Zinc, 25% Tin

The difference in appearance is very noticeable. In fact, when the sun peeked through the clouds, it was too bright to just stare at. The edges are rounded because the alloy cooled much less evenly than the aluminum did. They both have the feathering from rapid cooling while pouring, but a close up of the alloy bar revealed something odd that made the bar seem to sparkle.

The bar formed a hairlike pattern. This is apparently indicative of the brittleness of the alloy, and is present throughout. I ran it by ChatGPT and it credited the hairlike or needle like structures to: "Crystalline protrusions or solidification artifacts, very likely due to metallic phase separation and incompatible crystallization fronts. The fact that they're random in direction and extremely fine suggests intermetallic needles or whiskers forming as the alloy cooled—particularly from tin and zinc behaving erratically in the presence of aluminum." It went on a lot about it, but I'll leave the quote there. ChatGPT is often wrong about things I can verify, so I tend to grain of salt it on things beyond my comprehension. This is the end of the thought for now. Observations, not conclusions. I have taken the project much further, but further details are not read to be shared yet.