Use of 7075-T651 Aluminum for Splined Flange

[rxmelaun]

I would like to use 7075-T651 round bar to machine a sprocket flange that is driven by splines. My machinist is worried about cracking but I'm more worried about failure of the splines/flange if we use 2024-T4 (6061-T6 is out of the question). It's modulus is almost identical to 2024-T4 so I'd like to think it will work. Any insights?

 

[TVP]

First, is your machinist worried about cracking during machining or cracking during service? Second, elastic modulus is essentially the same for all aluminum alloys. Third, you likely need to be considering strength (yield, ultimate, shear, fatigue, etc.) and fracture toughness (resistance to crack propagation, flaw tolerance, etc.) not modulus.

 

[rxmelaun]

His worry is cracking during service not machining. I'm considering having the part electropolished and hard anodized. 7075 has higher fatigue strength, ultimate tensile strength, and yield strength but lower fracture toughness. Seems that it would be more resistant to any initial failure (assuming both parts are identical) but any crack, once started, would spread quicker. I guess that's the quandry.