Galling of Aluminum Alloys?

[easttiona]

I’ve recently switched Aluminum alloys and am experiencing a galling problem. I was looking for a source that could help me explain this problem.



My old system had Aluminum Alloy 850 T5 tempered rotating with .001”-.003” clearance on Aluminum Alloy 356 T6 tempered, with a soft Anodizing.



My new system has Aluminum Alloy 356 T6 tempered rotating with .001”-.003” clearance on Aluminum Alloy 319 F tempered, with a soft Anodizing.



I’m looking at the material properties and they seem to be better then the previous choices. Do you have any insight into if the material change is causing the galling problem?

 

[etch]

The alloy 850, if i am not mistaken has approx 1 % Cu and Approx 6 % Tin

Copper as an alloying element

Improves strength and hardness in the as cast and heat treated states, It improves machinability and thermal conductivity but, decreases corrosion resistance, stress corrosion resistance, ductility, castability and hot tear reisitance.

Tin

Improves anti0friction characteristics and machinability. Influences precipitation hardnening response in some alloys.

Tin reduces strenght and hot shortness.


A356 on the other hand is a very difficult material to machine, unless under the right conditions. This ally has about 0,5% mg and is other wise pure apart from 7.0 Si, Silicon decreases machineability in alloys.