aluminum threads and what grade alloy to use

[filterengineer]

Hi Guys

we're designing a new threaded filter can. it threads into a 6060 aluminum cast filter head with trapezoidal threads. I'm wondering if you fellas can give some tips on what would be the best material to use to avoid galling and thread wear. I realize I probably won't eliminate it all together but the part will be repeatedly installed and removed in order to replace the filter inside so I'd like to get the best materials possible to reduce the chances so to speak. Thanks Guys!

 

[SwinnyGG]

Are you absolutely sure that your mating part is 6060? You say it is a casting, but 6060 is a wrought alloy.

 

[filterengineer]

I may be wrong on the equivalent. Our drawing from the engineering department in Italy uses the euro standard specification of EN AB 46000 (AlSi9Cu3Fe)

 

[SwinnyGG]

That is helpful. That indicates that your mating part is most likely die cast, and has a hardness in the range of 80 Brinell(HB5).

The primary driver for galling resistance is selecting materials with a wide difference in hardness. I don't know what your other requirements are (corrosion protection, cast or machineability, weldability, etc) but you'll want to specify a temper for your new part that gets you up into the 120-140 range if you can.

 

[filterengineer]

Thanks for the info jhKRI. So 6061 with a T5 or T6 temper should work pretty well do you think?

 

[SwinnyGG]

6061-T6 is in the realm of 95 Brinell (HB5) vs approximately 80 (HB5) for EN AB 46000. For reference, this is about a 4-point spread on the Rockwell A scale.

That is a gap, but not a big one. My suggestion would be to hard anodize (not just cosmetic anodize, but hard anodize) the 6061-T6 part. The alternative would be to go to an aluminum 'super' alloy, such as 7075, but this would probably be more expensive than a hard anodized part would be. Hard anodize will bring the surface hardness way up, to 60+ rockwell C. That number is off the Brinell HB5 scale, so you'll have a huge hardness gap and the odds of having a galling problem should be low.

Note that if you go with a hard anodize coating, your part will grow by .001-.002", so if you have high precision fits anywhere you will need to design accordingly.

 

[filterengineer]

that's extremely helpful, thanks a bunch jg!