Choosing the right aluminum

[sg64]

I am designing a part that will be used as a mounting fixture and heat sink for a small printed circuit board. It needs to have a few 4-40 screw holes, haven't decided whether they will be tapped or use self-tapping screws. The part has no requirements for mechanical strength, it bears no loads, and it is not subject to vibration. It will be exposed indirectly to outside air, but not directly to precipitation, and its surface will never be visible, so finish quality is not an issue, and surface hardness is not an issue, either. The part is (roughly) cylindrical, about 1.5 inches in diameter and 1 inch high, so I expect it would be turned down from rod, then cut off and milled to remove a lot of the interior metal.

So the question is, How should I select the right aluminum for an application like this? What considerations apply? For example, does my choice of material affect the choice between using tapped holes or self-tapping screws? Does the material choice significantly affect the cost (time) to machine it? I assume that the material cost itself is overwhelmed by the machining cost for something this small--is that right?

I've read the aluminum descriptions, and it seems like any of them could work in this application, since I don't care about welding or mechanical strength, but I'd like to do better than flipping a coin. Thanks!

[Tech2]

In applications such as yours where there are really very few material considerations you generally want to go with the lowest cost. You can check which is lowest by trying each one and checking the price. Any aluminum can be tapped.

[sg64]

Thanks for the quick response!

Is there any difference among aluminums with respect to how well they will retain self-tapping screws? In some environments, the part will see a significant range of thermal cycling, from as low as -40 C to +40 or +50 several times per day.

[Tech2]

For that type of engineering assistance I would have to refer you to:
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