Honestly, when it comes to outdoor bench maintenance, the real difference is rust. Steel is strong, but most steel outdoor benches are not naturally weatherproof. They rely on a powder-coated or painted finish to keep moisture away from the metal. Once that finish gets scratched or worn, water reaches the steel and rust can begin. Aluminum does not rust, so its upkeep is less about preventing corrosion and more about keeping the finish clean.
For a steel outdoor bench, plan on a quick inspection every few months if it sits outside. Check the legs, feet, armrests, welded joints, and any place where water or dirt tends to collect. Wash it with mild dish soap and water, but skip abrasive scrub pads because they can scratch the coating. If you see a chip or scratch, touch it up promptly. Sand the area lightly, remove any rust, apply a primer or rust converter if needed, then paint over it. In humid, rainy, or coastal locations, rust prevention becomes even more important. Even galvanized and stainless steel benches are not completely zero-maintenance. Galvanized edges can corrode, and stainless steel can develop tea staining near salt air.
Aluminum outdoor bench maintenance is much simpler. You will still want to clean it once or twice a year, or whenever it looks dirty. Use warm water, a little mild soap, and a soft sponge or cloth. Rinse well, and that alone handles most of the upkeep. Over time, bare aluminum can develop a dull, chalky oxidation layer, and powder coating may fade or chalk. If that happens, a gentle aluminum cleaner or diluted vinegar solution can help on bare metal, but on powder-coated aluminum it is safer to stick with mild soap and water. A yearly coat of automotive paste wax or spray sealant can keep the finish looking fresh and make dirt slide off more easily. Scratches on aluminum will not turn into rust, so they are mostly a cosmetic issue rather than an urgent repair.
The cleaning routines overlap a little. Both benches need occasional washing, and both benefit from keeping joints free of standing water and debris. The difference is how urgently you need to respond to damage. A scratched steel bench needs fairly prompt attention before the problem grows. A scratched aluminum bench can usually wait until you feel like touching it up. Steel may need repainting every few years if the coating breaks down, while aluminum rarely needs repainting unless you want to restore the color.
If you want the lowest-effort option, choose aluminum. It is especially forgiving in coastal or rainy climates. If you prefer the heavier, planted feel of steel and do not mind a little seasonal touch-up and rust inspection, a well-made powder-coated steel bench can still be a great choice. Just treat chips early, keep it clean, and do not let rust get started.