Is it OK to screw a steel screw into aluminum?
Is it OK to screw a steel screw into aluminum?
(OP)
If we disregard galvanic corrosion, is it OK to screw a #8-32 a low strength steel screw into 3/16" thick aluminum sheet? I seem to remember that it is not generally recommended because the aluminum like 5052-H32 is not as hard as a steel screw and that is why we use helicoils. But what about if you use 6061-T6 aluminum? It appears to have a Rockwell B hardness of about 60 and a tensile strength of about 47,000 psi. This may be harder than a low cost low strength hardware store zinc plated screw, right? So would the steel screw work ok in 6061-T6 aluminum or is there some other consideration that I have not thought about?





RE: Is it OK to screw a steel screw into aluminum?
RE: Is it OK to screw a steel screw into aluminum?
Whether installing a zinc plated low cost low strength #8-32 hardware store steel screw directly into a tapped hole in 3/16" aluminum plate is "OK", that's between you and your customer.
RE: Is it OK to screw a steel screw into aluminum?
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RE: Is it OK to screw a steel screw into aluminum?
RE: Is it OK to screw a steel screw into aluminum?
Minimum typical thread size for a screw threading into aluminum in that application is M6x1.0 and with more thread engagement than you are proposing, though.
I use a torque wrench on every single fastener. Gorillas will do damage.
RE: Is it OK to screw a steel screw into aluminum?
RE: Is it OK to screw a steel screw into aluminum?
Thanks. That probably explains why I munged one of my carburetor threads a long time ago. It galled so bad that the screw took all of the thread with it.
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RE: Is it OK to screw a steel screw into aluminum?
I systematically call up helical thread inserts for airborne stuff. On occasion, I have had to make the choice of thread inserts or larger screws, for example, edge of 1/4" plate and 6-32UNC and helicoils versus 8-32UNC screws. I went for 8-32UNC. I now know that aircraft approval people don't like screws into edges of plates, helicoiled or otherwise.
If the thing is going to be taken apart a lot, I recommend thread inserts. If it does not fly, and you are in control of the assembly and the screw torque, and it does not come apart, you don't need the inserts.
Have you considered press-in nuts like PEM? These may be cheaper than tapping the holes. The floating ones cost more, but they let you get away with sloppier tolerances. The float typically accounts for sheet metal bending tolerances.
--
JHG
RE: Is it OK to screw a steel screw into aluminum?
Coincidentally I'm building something with 3/16" 6061 T6 and #8-32 flat head socket screws. I'm using nuts on the screws, but I've tried threading them into the aluminum. As mentioned by drawoh, the threads in the aluminum quickly become loose if you reassemble several times.
RE: Is it OK to screw a steel screw into aluminum?
One thing you have not mentioned is the usage of this screw. Is this a one time insertion , or does this screw have to be removed and replaced frequently.
The Helicoil increases the effective diameter of the steel portion in the aluminum and gives you a more gall resistant surface on the screw threads.
If a rolled thread tap is used to tap a 3/16" thick Aluminum plate, the work hardening of the threads will reduce the tendency to gall a little, versus a cut thread.
When all else fails do a test.
B.E.
You are judged not by what you know, but by what you can do.
RE: Is it OK to screw a steel screw into aluminum?
RE: Is it OK to screw a steel screw into aluminum?
RE: Is it OK to screw a steel screw into aluminum?
Hole prep is a little easier than countersinking, you just press 'em in, and you don't have to worry about them working loose.
Mike Halloran
Pembroke Pines, FL, USA
RE: Is it OK to screw a steel screw into aluminum?
RE: Is it OK to screw a steel screw into aluminum?
Ted
RE: Is it OK to screw a steel screw into aluminum?
RE: Is it OK to screw a steel screw into aluminum?
RE: Is it OK to screw a steel screw into aluminum?
We put SST fasteners into threaded holes in aluminum all the time in 'non structural' joints in fairly benign environments (think office or lab) with few issues.
On sheet metal we routinely use pem type fasteners.
All comes down to more detailed application information as to whether it's right for you.
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