Kinaguiden is a precision aluminium die casting company based in Stockholm, Sweden, specialising in custom mould design, HPDC, re-engineering, and global logistics.
The surface finish on an aluminium die casting affects appearance, corrosion resistance, hardness, and in some cases electrical properties. Choosing the right finish — or combination of finishes — is as important as alloy selection. This guide covers the most common post-casting surface treatments and helps you match them to your application.
As-Cast Surface
Fresh from the die casting mould, aluminium parts have a smooth metallic surface with parting line flash, ejector pin marks, and gate witness marks removed by deburring and trimming. As-cast surfaces typically have a roughness of Ra 1.6–3.2 µm. For many internal or non-visible components, the as-cast surface is entirely acceptable and requires no further treatment.
Shot Blasting
Shot blasting propels small steel or glass beads at the part surface at high velocity, creating a uniform matte texture and removing surface oxides. It is usually the first step before any coating process, as it improves coating adhesion. Shot blasting alone (without a subsequent coating) provides a consistent matte appearance but limited corrosion protection.
Anodizing
Anodizing is an electrochemical process that converts the aluminium surface into a hard, dense aluminium oxide layer. It significantly improves corrosion resistance and surface hardness, and can accept dyes for colour. There are three main types:
- Clear / Type II anodize — 8–12 µm thick layer. Provides good corrosion resistance and a natural aluminium appearance. The most common choice for architectural, consumer, and lighting applications.
- Colour anodize — Type II with an added dye step. Produces consistent colour in black, gold, bronze, red, blue, and other colours. UV-stable for outdoor use.
- Hard anodize / Type III — 25–50 µm thick layer. Extremely hard surface (comparable to case-hardened steel). Used for wear-resistant applications — sliding components, hydraulic housings, military and aerospace parts.
Note: Not all HPDC alloys anodize equally well. High-silicon alloys like ADC12 produce a darker, less consistent anodize than low-silicon alloys like A360. If anodizing is critical, alloy selection should account for this.
Powder Coating
Powder coating applies a dry polymer powder electrostatically and then cures it in an oven, forming a continuous, thick coating (typically 60–100 µm). It provides excellent corrosion resistance, a wide range of colours and textures (matt, gloss, metallic, wrinkle), and is highly UV-resistant for outdoor applications.
Powder coating is less hard than anodizing and can chip under impact, but it covers parting lines and surface defects better and is generally more cost-effective for high volumes. It is the standard finish for outdoor lighting, architectural panels, and industrial equipment enclosures.
E-coating (Electrocoating)
E-coating (also called electrocoating or KTL) deposits a thin, even paint layer (15–25 µm) using an electric current in a liquid paint bath. Because the coating is applied electrically, it reaches into recesses, holes, and internal surfaces that spray painting cannot access. E-coating provides excellent corrosion protection and is commonly used as a primer under powder coating or paint, particularly in the automotive industry.
Chemical Conversion Coating (Chromating / Alodine)
Chemical conversion coating applies a thin chemical layer to the aluminium surface, improving corrosion resistance and paint adhesion without adding significant thickness. It is used primarily as a pre-treatment for painting or as a standalone protective layer for electrical/electronics applications where dimensional precision must be maintained. RoHS-compliant trivalent chromate versions are available.
Choosing the Right Finish
| Application | Recommended Finish |
|---|---|
| Indoor, non-visible structural part | As-cast or shot blasted |
| Decorative consumer product | Clear or colour anodize |
| Outdoor enclosure or lighting | Powder coat or colour anodize |
| Automotive body / chassis | E-coat primer + topcoat |
| Wear-resistant sliding surface | Hard anodize (Type III) |
| Electronics EMI shielding | Chromate conversion + as-cast |
| Marine or saltwater exposure | A360 alloy + hard anodize or powder coat |
Kinaguiden coordinates all finishing in-house. We arrange shot blasting, anodizing, powder coating, and e-coating as part of our post-processing service — delivering fully finished, inspection-ready parts direct to your door.