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After CNC machining of aluminum parts, surface treatment is typically applied to protect the components and meet specific assembly requirements, as aluminum is a metal that readily undergoes self-oxidation.
Next, we will discuss several common surface treatments used after CNC machining of precision aluminum parts and their respective characteristics:
Surface treatment for precision aluminum part machining:
Sandblasting—though this is a colloquial term used in Guangdong, the actual process is shot blasting—can be carried out using a shot-blasting machine that pressurizes and propels garnet abrasive onto the metal surface. By varying the grit size of the garnet (expressed in mesh size), a matte, frosted finish can be achieved on the metal surface.
It is typically used in lighting fixtures and furniture. This process only enhances the texture of the material’s surface; a subsequent anodizing step is required to achieve special, vibrant colors.
Here’s a photo of our company’s aluminum parts after CNC machining, sandblasting, and anodizing.
It can be seen that after sandblasting and anodizing, the aluminum part has a grainy surface texture; combined with the silver anodizing finish, it appears noticeably brighter than standard aluminum parts.
Disadvantages: Shot blasting is relatively difficult to control in terms of pressure, and automated equipment requires repeated trials and adjustments to achieve optimal settings. Moreover, the deformation induced by this process is substantial; therefore, it is not recommended for open-section aluminum extrusions or thin-walled components, or else sufficient deformation allowance should be incorporated during the fabrication of the blank parts.
Another method to avoid the deformation effect is alkali-sandblasting, which is commonly used for many aluminum-finish residential wall-mounted water heaters in Europe. The result is very similar to sandblasting, though it lacks the tactile texture of sandblasted surfaces; visually, the two are comparable, with a darker, more refined appearance. However, it does not achieve the bright, lustrous, and vivid colors typical of anodized finishes.
Another process is spray coating, which can also produce an effect that mimics oxidized sandblasting. A key advantage is that the color looks virtually indistinguishable from anodized aluminum; however, the surface has a glossy, oily sheen, as if the anodized layer had been coated with a clear varnish. This method can be used to treat plastics as well, but the plastic material must be able to withstand a certain temperature—otherwise it will deform or soften when exposed to high-temperature ovens. Sprayed coatings produced using this technique do not discolor or flake off due to overheating, and they are also more resistant to scratching.
Here’s a picture of a green anodized aluminum part. Anodizing offers a wider range of color options and provides excellent protective properties. In general, anodizing is a suitable surface treatment for parts that will be exposed on the exterior, as it enhances both aesthetics and durability.
Aluminum parts can also be powder-coated, but this process typically incurs higher machining costs; therefore, many products use powder coating on steel, while aluminum is usually anodized to impart color and protect the material from oxidation and blackening.
Recently, we’ve also been developing an oxidized, brushed-aluminum switch panel with a faux antique-bronze finish. This type of product tends to be well-received by customers who place a high value on interior design, as its edges are sharper and more crisp compared with standard plastic components, and its tactile quality avoids the clichéd, mass-produced look often associated with plastic switches. This finishing process can be applied to a wide range of lighting fixtures, steel-tube furniture parts, and even circular baseplates and tabletops that require precision machining on rotary tables.
Let’s now discuss a special aluminum-part treatment that may not fall under conventional surface-finishing processes. In certain mechanical applications, it is necessary to maintain the overall weight of the assembly; however, aluminum parts generally have lower hardness and density—and thus poorer wear resistance—than steel components. To address this, we can insert hardened steel inserts into the threaded holes where the aluminum part interfaces with other components. This approach preserves the lightweight advantage of aluminum while enhancing wear resistance to match that of stainless steel.