The problem both are solving
Hardwood decking in this climate is a maintenance commitment. Sun, daily heat cycling and monsoon rain mean sanding, staining and sealing on a schedule, and the schedule is the part nobody keeps to.
Aluminium and wood-plastic composite both remove that schedule. Neither needs sealing. Both are why most decks we lay now are not timber.
What wood-plastic composite gives you
WPC is a board of wood fibre and polymer with a grain embossed into the surface. From standing height it reads as timber, which is the point, and it is the friendlier budget of the two.
It cuts and frames like a board, so it takes a curve, which matters more often than people expect. A garden terrace that follows a planter line is straightforward in composite and expensive in anything else.
It does get warm in direct sun, like any dark surface, and darker colours warm faster.
What aluminium gives you
An aluminium board is an extrusion, usually hollow, usually with a wood-grain finish applied. It does not absorb water at all, it does not swell, and it spans further, so the frame under it can be lighter.
It is the more durable of the two and it costs more. Where it earns that is on fully exposed installations: a roof terrace with no shade, a deck that takes standing water in a downpour, anywhere the surface is in the weather all day every day.
How to choose
Ask how exposed the deck is. Covered balcony, either works and composite is the value answer. Fully exposed roof terrace in the sun all day, aluminium is the one that will still look right in a decade.
Ask whether the shape is straight or curved. Curves favour composite.
Ask what is underfoot. Both get warm in direct sun; lighter colours and a shaded aspect help more than the material choice does.
And ask to stand on both. We keep samples at the Ubi showroom. The difference underfoot is obvious in ten seconds and describes itself better than any specification sheet.
One honest caveat on photographs
Aluminium decking is commonly sold with a wood-grain finish, which means a photograph of a finished deck often cannot tell you which material it is. Do not choose from a gallery, ours included.
The board material on your job is named in your written quotation. If a quotation does not name it, that is the thing to ask about.