Short answer: aluminium and galvanised parts can be powder coated. On aluminium the natural oxide layer must be removed and replaced with a controlled conversion layer; on galvanised steel the zinc surface must be prepared and outgassing in the oven prevented.
Aluminium
Aluminium covers itself with a thin natural oxide layer the moment it meets air. That layer protects the metal but its thickness and structure are uncontrolled; it is not a sound base for the coating to bond to. Pretreatment removes it and puts a measured, repeatable conversion layer in its place.
Extrusion versus casting: extruded profiles are clean and predictable in surface terms. Cast aluminium can be porous; air and moisture held in the pores expand in the oven and open pinholes in the film. Preheating (degassing) lowers that risk on castings.
Architectural work: for aluminium used on façades, powder selection matters as much as thickness; polyester or polyurethane-based powder is needed for UV resistance.
Galvanised steel
A hot-dip galvanised surface provides a second corrosion barrier under the paint — done correctly, coating life is markedly longer than on bare steel. Three points need attention:
- White rust. White zinc oxide forming on galvanised surfaces that take up moisture in storage prevents adhesion and must be removed before pretreatment.
- Outgassing. Air held in the zinc layer and the pores beneath expands at oven temperature and leaves pinholes as it escapes through the film. Preheating the part in the oven before coating largely removes that risk.
- Surface roughness. A galvanised surface is rougher than steel; film thickness may need to run slightly higher to reach the same visual result.
What to state in your enquiry
- Material: aluminium (extrusion / casting / sheet) or galvanised (hot-dip / electro).
- For galvanised parts, the galvanising date and storage conditions — these indicate the white rust risk.
- Whether the part will be used indoors or outdoors.
- Any existing coating specification or customer standard.
These four pieces of information determine the pretreatment parameters we work with and the powder type we select. Tell us the material of your part, and we will settle the right line and any preheating requirement together.