Aluminum Die Casting Shot Blasting: Prevent Embedding & Corrosion

Abrasive Selection: Avoid Carbon Steel Shot; Opt for Stainless Steel Shot

Do not use standard cast steel or cast iron shot. Technical literature clearly indicates that when ferrous (iron/steel) media are used on non-ferrous metal parts (such as aluminum or magnesium), fine iron particles generated during impact can contaminate the surface and induce electrochemical corrosion—necessitating an additional cleaning step after the shot blasting process.

Recommended Solutions:

· Stainless Steel Shot (Grade 304 or 430): This is the industry-standard choice for shot blasting aluminum die castings. It is rust-resistant, exhibits a low fracture rate, preserves the natural metallic appearance, and eliminates the need for post-process acid pickling.

· Recommended Mix: Some patented processes utilize a blend of 304 stainless steel spherical shot and cut-wire shot, typically in a ratio of 3:1 or 5:1. A relatively gentle set of parameters—using 0.6mm diameter spherical/cut-wire shot, a blasting frequency of 26Hz, and a duration of 19 minutes—is effective for removing burrs and flow marks (water marks).

· Enhancing Surface Luster: If the client requires a specific level of surface gloss, 10%–20% aluminum shot (with a particle size of 0.6–1mm) can be added to the media mix. The aluminum shot acts as a polishing agent, increasing surface brightness while simultaneously reducing roughness.

Equipment Selection: Prioritize Mesh-Belt Systems; Exercise Caution with Tumble-Belt (Barrel) Systems

· Small to Medium-Sized Parts (Batch Processing): A mesh-belt pass-through shot blasting machine is the preferred choice. Workpieces are transported in a single layer without being compressed against one another, which prevents thin-walled aluminum components from sustaining impact damage or deformation. For this type of equipment, the shot velocity ranges from 60 to 80 m/s, and the surface roughness can be consistently maintained between Ra 1.6 and 6.3 μm, making it suitable for pre-treatment prior to coating.

· For complex-shaped or large components: A overhead-conveyor (hanging) system is recommended, allowing the workpiece to rotate 360°. The shot particle size can be adjusted within a range of 0.2–3 mm, offering high flexibility.

· Exercise caution with tumble-belt (barrel-type) systems: As workpieces tumble and collide with one another, soft aluminum parts are prone to scratches and dents; therefore, this method should be used with care for parts where surface appearance is critical.

Key Process Control Points (demonstrating professional expertise during client discussions)

1. Prompt downstream processing after shot blasting

Shot blasting creates tiny pits on the aluminum surface, which can trap processing fluids or cleaning agents. If left in a humid environment for an extended period, residual steel shot fragments can trigger a galvanic reaction with the aluminum substrate, resulting in the formation of white or gray powdery corrosion products. It is advised to move parts immediately to the next stage—such as cleaning, passivation, or coating—rather than leaving them exposed.

2. Effective dust removal and media-debris separation

Excessive dust or unremoved debris within the steel shot can cause the entire surface of the workpiece to appear dark or blackened. Verify with the client whether their shot-blasting machine is equipped with an efficient magnetic separator and vibrating screen, and ensure that the shot recovery rate is at least 95%.

3. Aligning surface roughness with subsequent processes

If the parts are destined for subsequent anodizing or high-gloss coating, the surface roughness must be kept to a lower level. In such cases, begin testing with a particle size of 0.3–0.6 mm; using larger media could create deep pits that the coating may fail to cover. A Concise Opening Pitch

“When shot-blasting aluminum parts, there are two main concerns: first, steel shot fragments can become embedded, leading to the appearance of white spots after just a few days; second, if the shot size is too large, the surface may become overly rough—to the point where a subsequent coating can no longer cover it. I recommend using 304 stainless steel shot, blended with a portion of aluminum shot to enhance brightness. We could start by running a test batch—using just a few dozen kilograms—on your mesh-belt line, applying your current process parameters. We can then evaluate the surface roughness and check the condition of the parts after a week before making a final decision.”