Aluminium 5083 should work well in keeping the weight low for your enclosure. However, if stiffness is more critical, steel would provide better rigidity, though it would significantly increase the weight, by 2 or 3 times.

Alternatively, a hybrid design—using Aluminium for the outer panels and plated mild steel for some internal structural elements – could strike a good balance between weight and stiffness.

If you want a stronger aluminum, you could consider also the 6XXX series: 6061, 6082.

Depending on the corrosion environment, another good choice would be 7075 with a good coating. For example, in salt environments, the 7075 is not a good choice due to Cu content of ~2%.

5083 aluminum has lower stiffness (elastic modulus ~70 GPa) compared to steel (~200 GPa), but offers advantages in weight, corrosion resistance, and machinability. For compact keyboards:

Prioritize structural design validation: Topology optimization (e.g., reinforcing ribs, localized thickening) can compensate for stiffness and typically meet low-frequency mechanical load requirements.
Vibration considerations: Use steel if key actuation frequencies align with the structure’s natural frequencies (due to steel’s higher damping), otherwise aluminum with vibration-damping pads suffices.
Alternatives: 6061-T6 aluminum (slightly better strength/stiffness) or locally embedded steel bushings to balance performance and weight.
Conclusion: 5083 aluminum is generally viable with optimized design. Steel is only necessary for high-frequency/high-impact loads. Finite element modal analysis is recommended for verification.