The Rays nuts are not just made of aluminium, hence their name Duraluminum and as stated aircraft grade Aluminium (and that probably is the stuff we eat on the plane).
The Aluminium is blended with other materials as exampled below to increase its strength yet remain lightweight.
A commonly used modern equivalent of this alloy type is AA2024, which contains 4.4% copper, 1.5% magnesium, 0.6% manganese and 93.5% aluminium by weight. Typical yield strength is 450 MPa (65 ksi), with variations depending on the composition and temper.
Stainless Steel has a yield strength of 520mpa
Aluminium 6061-0 has a yield strength of 45mpa
Aluminium 6061-T4 has a yield strength of 110mpa
So Duraluminum with a yield strength of 450mpa should not be shunned off for just being 'Aluminium'.
It all depends on the lug nut and its construction type, as exampled above. Who's to say what the copy lugs are made of.
True Duralumin is not untrustworthy. Which I'm sure Rays wouldn't put their name to if they weren't up to the job.