I know that at least one of you here has experience casting metals, so that is why I pose this question here rather than on some more appropriate forum where I don't know anyone.
I am trying to design the most efficient propeller possible for a human powered boat (pedal boat). In the pictures below you can see a metal propeller made by Rick Willoughby who is arguably the foremost expert in high performance pedal boats. It is a proven efficient design, I hope to at least equal its performance, if not exceed it.
In case you don't know, when it comes to efficiency in foils wether they be propellers or airplane wings or hydrofoils etc, the ideal is to have a high aspect ratio (long and skinny) in order to affect the greatest volume of fluid just a little bit; as opposed to affecting a small volume a whole lot to get the same amount of thrust/lift.
I have 3d printed quite a few propellers and blades but so far have only tested the white one seen in the first picture. We could not perceive a difference in performance between it and the crude stock propeller that the pedal drive came with. Not surprising since the 3d printed propeller was not very smooth and had a very blunt trailing edge. It was far from ideal but it did prove that a FDM printed propeller can hold up to the forces involved - at least when printed at that thickness.
The blades that I have resin printed have turned out very nice and surprisingly strong. They require only a little wet sanding to make them very smooth, nice sharp trailing edges too. For the relatively meager power that they need to absorb I think they will do fine for testing.
My problem is that longer skinnier blades will not hold up - they may not break but they would bend too much, and the long skinny blades are where the best efficiency will be. I will need to either make them out of composites or metal.
Now for the question; what is the strongest metal that melts at a low enough temperature to be used in silicone molds? From what I have read, pewter and zinc can be cast in silicone molds. The blades only need to be strong enough for testing, not consumer use. Injecting epoxy into a mold that contains something to strengthen it might also be a possibility - but I think metal would be simpler. If it is strong enough.
I am looking for a solution that will allow me to 3d print lots of different blades, make molds then make test blades from those molds - later when I have settled on the best blade I can pursue a solution for casting it in something durable, like bronze.