Key Characteristics

The surface appears normal prior to shot blasting, with peeling or flaking becoming visible only afterward. Fundamentally, this indicates a subsurface delamination defect; the impact force of the shot blasting removes the poorly bonded surface layer, exposing the underlying issue.

Primary Causes

I. Root Causes Originating from Die Casting (Accounting for >80%)

1. Surface Cold Shuts/Cold Skins:Thin layers of solidified metal formed by molten aluminum splashing against the mold cavity wall; these bond poorly to the base material and detach under shot blasting impact.

2. Subsurface Porosity/Pinholes:A high density of minute hydrogen pores beneath the surface; once shot blasting removes the dense outer skin, these pore clusters are exposed, creating a "pitted/peeling" appearance.

3. Surface Porosity/Looseness: Insufficient injection pressure or delayed intensification pressure results in low surface density and poor impact resistance.

4. Residual Release Agent Layer:Mold release agent is forced into the surface layer, creating an intervening separation layer that flakes off in sheets after shot blasting.

II. Contributing Factors from the Shot Blasting Process

1. Excessive Shot Blasting Intensity: Shot diameter is too large (e.g., >1.0 mm) or projection velocity is too high, directly stripping away the surface layer.

2. Perpendicular Shot Angle:Shot particles striking the surface vertically generate high shear forces, making it easy to tear off the surface layer.

3. Excessive Shot Blasting Duration: Over-processing leads to repeated erosion/cutting of the surface layer.

4. Improper Shot Selection: Using steel shot instead of aluminum or stainless steel shot; the hardness and impact force are incompatible with the aluminum alloy.