Dissimilar Metals

[Weldingiron]

Tonight while deburring ribs it occurred to me that, while we make a point never to use steel wool or silicon carbide sandpaper on aluminum parts, router bits, round files and deburring tools made of steel seem to be acceptable. Is the introduction of carbon a non-issue with these tools or is their acceptance based on lack of an alternative?

[fairchild]

I think its a matter of if microscopic bits of the foreign object are going to break off and be injected into the lattice crystal structure of the aluminum. The foreign objects act like an imbedded wedge
and create stress and hardness at that spot. Then- because thats a local hard spot--- the crack starts there. But its more complicated than just invisible splinters. some elements or molecules
can be shoved into the latticework---- and if they are a correct size and electric charge--- they can take the place of an aluminum atom and everything is happy. If the thing is in the same
periodic table colum as aluminum--- it fits and is happy. As you move left or right--- gradually less so. Probably even more complicated than that ---
They use this process of substatution in making computer chips. They add other elements into silicon from the same column to change the electrical behavior of the material.

Carbon in steel kind of works the opposite way. The carbon falls out of solution as the steel cooks and the carbon forms clumps which stress the steel lattice. And the stress makes the material more rigid. But as it get harder from the carbon---- it gets easier and easier to induce a crack from stress or corrosion. These intruders cause stress and that stress makes corrosion thart there
where it would not have otherwise. This is why if a steel part is heat treated too far--- it gets too hard and breaks early --- ahead of its expected lifetime. You see this on the knifemaking TV
shows. Too hard--- drop it on the floor--- breaks like glass..... :-) bet you didnt expact a crazy answer like this did you ? :-)

T
PS
dont use steel wool on wood if it has not been sealed. Only after. The bit get driven into the grain--- then they turn black and look like specks of black paint. after you do some kind
of treatment to fill the grain -- it wont go in. Learned that the hard way making violins.

[Weldingiron]

Thanks! Definitely more in depth than I expected but good stuff. Who would have thought chemistry had a place at the homebuilders table

[Archer39J]

Honestly we're not building space shuttles here. So I figure while I won't use anything like steel wool if I happen to use a file on steel then aluminum I'm not going to sweat it too much.

[way_up_north]

Tonight while deburring ribs it occurred to me that, while we make a point never to use steel wool or silicon carbide sandpaper on aluminum parts, router bits, round files and deburring tools made of steel seem to be acceptable. Is the introduction of carbon a non-issue with these tools or is their acceptance based on lack of an alternative?

It’s a good question...

how I look at it is iron or whatever is getting into the cut... but the deburing and finishing of the edge removes the contamination... the idea that the contamination is right at the site of the cut edge

but this is also why you would not use steel wool to work on scuffing up a wing skin for painting as you’re putting contamination into an area that is not going to be removed...

[davzLSA]

Scotch brite pads and wheels works great on aluminum, it is not as hard as steel so you dont need the steel tools to finish the cut surfaces, then the steel that would be deposited by cutting tools would be removed by the scotch brite products. Like as been said just dont use steel products to finish the cuts.

[Gerhard Rieger]

Hi, I have two files that I only use on aluminum and cutting disc's on my grinder gets marked Alu so not to get microscopic steel embedded into it and then transfer that to the Aluminum.