# Thread: how hard is 7075

1. ## how hard is 7075

How hard is aluminum 7075 to lathe? Its the hardest but it is still Easy and easy on the tools?

2. Your question is not complete, 7075 comes in a number of tempers F, O, H, W and T. There are 3 subdivisons H1 H2 H3. The degree of Strain hardened are next and follow the second digit following one of the two above, 2 = 1/4 hard, 4 = 1/2 hard 6 =3/4 hard, 8 = full hard. and lastly 9 = extra hard.
Anyway the most common 7075-T6 or T651. It is very nice to machine and has a tensile strenght of 83,000 psi and yield of 73,000 psi. So to kind of answer your question... if I look up 83 ksi that = 170 Brinell hardness. However most references list it at only 150 Brinell and I'm not sure why.
Steve

3. 7075 Al is a blessing to machine. It's hardness makes it machine in a "crisp" manner, low galling on tools. Any AL specific tooling (sharp) is a good start for lathe and mill. Just beware that if you remove a lot of material from for example one side of a plate, it will warp(banana) when the stress is relieved from the one side. In other words doing a rough cut on both sides of part before machining final surfaces might be in order.

Drill 1/4"-3/8" hole in drill press first into 6061 and then 7075, you will understand what crisp means...

4. its for T651. Thanks