Many components on an outboard motor are aluminum such as the lower unit. I’m not a metallurgist, but I want to learn how different metals like aluminum and steel interact when put in water and subjected to different petroleum products. I also want to keep in mind the density and strength of metals so I choose a screw strong enough to avoid breaking, but not too strong to damage the aluminum.
As I dismantle outboard engines for parts, I find plenty of rusty screws that I’d like to replace as I rebuild a magneto or rebuild a lower unit. In the past I’ve just gone to a hardware store to buy screws, but not all metals are the same. I found this reference helpful: http://navybmr.com/study%20material/14250a/14250A_ch1.pdf
The first thing I do which is super easy is to put a magnet to the screw or part to see if it is steel or another metal. If steel the magnet attracts it. If aluminum, brass, etc. it does not. My next step will be using the reference above. I’ll be observing the colors of the screws and observing sparks from my bench grinder with some of these screws that I salvage.
By the way, in a lower unit I just disassembled I found studs that were steel and others that were aluminum. My guess is the aluminum studs may have been replacements, but I will try to figure that out over time. I know one retired Mercury mechanic. I’ll try to find some old timer design engineers from Mercury.
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