Q: Can you suggest a different material with similar strength-to-weight ratio as the 7075, that can be produced with a diameter M3-0.5?
A: Since an M3 bolt is too small to be produced from Aluminum 7075, I would suggest either grade 2 titanium bolts or grade 5 titanium bolts. For the most superior strength to weight ration, you should consider Titanium Gr5. Also, Titanium Gr2 will get you close to the strength of Aluminum 7075-T6 but not quite. See the following charts which will show the strength of titanium for both grades.