Static friction coefficient represents the resistance that must be overcome to initiate motion between 2 stationary surfaces
Dynamic friction coefficient represents the resistance that must be overcome to sustain motion between 2 sliding surfaces

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Bare aluminum is one of the worst metal-on-metal sliding combinations in mechanical design.

Severe galling and micro-welding: Aluminum instantly forms a microscopically thin oxide layer (Al2O3). Under the friction and pressure of sliding, this brittle layer shears off, exposing raw metal. The bare surfaces immediately cold-weld to each other at the microscopic contact points, causing severe galling, tearing, and mechanical seizing.

Extremely High Friction: Dry aluminum-on-aluminum has a static coefficient of friction typically exceeding 1.0 to 1.35, creating massive resistance and rough, jerky stick-slip movement.

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Why Powder Coat Performs Better:

Powder coating is applied by electrostatically charging powder polymer particles and spraying them on metal. The part is then baked in an oven to cross link the polymers into a permanent 3D network.
Polymer on Polymer Contact: Powder coatings are thermoset polymers i.e. plastics that once cured cannot be melted, as opposed to thermoplastics like nylon, PLA, Teflon (PTFE), Lexan (polycarbonate), etc. Polymers used for powder coating are usually polyester, polyurethane, or epoxy. Sliding two coated pieces against each other creates a polymer-on-polymer interface rather than metal-on-metal.
Lower Friction Coefficient: Smooth polymer surfaces typically have a friction coefficient between 0.2 and 0.4, resulting in noticeably smoother travel and no risk of metallic galling.

Material                             Static        Dynamic
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Dry bare Aluminnum on Aluminum       1.05-1.35+    1.00-1.40
Smooth powder coat on powder coat    0.35-0.45     0.25-0.35