In the production of aluminum die castings and zinc die casting parts, maintaining consistent appearance and performance is critical. However, factors such as mold design, process parameters, material purity, and operating practices often lead to casting defects. These imperfections not only affect the aesthetics of the part but can also reduce its mechanical strength and reliability.
This article introduces 18 of the most common die casting defects, explains how to identify them, and provides detailed solutions to help manufacturers and engineers improve the quality of their castings.
Appearance: Linear scratches or grooves along the mold opening direction; in severe cases, large surface areas are torn.
Detection: Visible scratches on the surface, typically near ejector marks or mold parting lines.
Solutions:
Mold/Design: Polish the cavity surface; increase draft angle; balance ejector pin layout; secure loose inserts to avoid misalignment.
Process: Maintain stable mold and melt temperature; optimize injection velocity transition point; delay ejection until solidified.
Materials: Adjust iron content in aluminum alloys to reduce sticking; use high-quality release agents with uniform coating.
Verification: Apply mold-checking agents (e.g., bluing) to confirm contact areas.
Appearance: Wavy streaks, cloudy lines, or discoloration on the surface.
Detection: Easily identified during visual inspection.
Solutions:
Mold/Design: Increase gate cross-section or adjust gate position; add overflow vents.
Process: Raise pouring and mold temperature to achieve stable thermal balance; optimize injection velocity profile.
Materials: Reduce excessive die coating to prevent streaks.
Verification: Adjust parameters step by step and monitor surface improvement.
Appearance: Irregular, seam-like lines resembling cracks or dendritic patterns.
Detection: Surface inspection or revealed after machining.
Solutions:
Mold/Design: Shorten flow length by optimizing gating system; add exhaust vents.
Process: Increase melt and mold temperature; optimize switchover point and intensification pressure; extend holding time.
Materials: Use low-gassing die coatings; reduce excessive spray cooling.
Verification: X-ray inspection or fracture surface analysis for continuity.
Appearance: Unfilled sections, blurry or missing edges.
Detection: Easily spotted on the part surface.
Solutions:
Mold/Design: Add overflow vents; optimize gate thickness and location for full cavity filling.
Process: Increase melt temperature, injection pressure, and velocity; reduce back pressure.
Materials: Ensure clean alloy feedstock with good fluidity; avoid excessive die lubricant.
Verification: Record filling completeness using cavity pressure or video monitoring.
Appearance: Thin excess metal sheets along the parting line or ejector areas.
Detection: Visual inspection.
Solutions:
Mold/Design: Resurface parting line; restore worn inserts or slides; improve mold rigidity.
Process: Adjust clamping force and injection speed; adopt closed-loop injection control.
Production control: Clean mold surfaces frequently to prevent contamination.
Verification: Monitor flash thickness as a process capability index (Cp/Cpk).
Appearance: Geometric shape deviates from design; often occurs in thin-walled parts.
Detection: Dimensional measurement against CAD drawing.
Solutions:
Mold/Design: Optimize cooling channels; balance ejector pin layout; adjust gate size to reduce residual stress.
Process: Extend holding and cooling time; maintain uniform mold temperature; use staged ejection.
Post-treatment: Apply stress-relief heat treatment or mechanical straightening if necessary.
Verification: Use in-line dimensional gauges to monitor deformation trends.
Appearance: Smooth, round cavities within the casting.
Detection: Sectioning or X-ray inspection.
Solutions:
Mold/Design: Provide sufficient venting and overflow; apply vacuum die casting for deep cavities.
Process: Optimize injection velocity and switchover point; maintain stable intensification pressure.
Materials: Use clean feedstock; degas properly; reduce release agent application.
Verification: Conduct hydrogen content or density index (DI) tests.
Appearance: Irregular, rough-surfaced voids, often in thick-wall areas.
Detection: X-ray or ultrasonic inspection.
Solutions:
Mold/Design: Ensure uniform wall thickness; increase localized cooling; redesign gate system to deliver pressure to last solidifying areas.
Process: Increase intensification pressure and holding time; lower melt temperature; use a thicker biscuit to improve feeding.
Production strategy: Introduce pre-machined holes in non-critical zones to shift shrinkage away from functional areas.
Verification: CT scan and metallography in hot-spot sections.
Appearance: Irregular dark spots or hard inclusions inside the casting.
Detection: Revealed after machining or metallographic analysis.
Solutions:
Melting/Handling: Use clean alloy ingots; refine and degas; skim slag thoroughly; pour smoothly to reduce turbulence.
Maintenance: Clean furnace lining, crucible, and shot sleeve regularly.
Verification: Metallographic evaluation and black spot density check after machining.
Appearance: The casting fractures easily, grain structure abnormal.
Detection: Mechanical property testing or fracture analysis.
Solutions:
Materials: Control impurity levels (Zn, Fe, Pb, Sn); adjust composition with master alloys instead of powders.
Process: Avoid overheating and long holding times; maintain suitable mold temperature.
Verification: Regular tensile and impact strength tests.
Appearance: Parts fail pressure or leakage tests, leaking air, oil, or water.
Detection: Air-tightness or hydraulic test.
Solutions:
Mold/Design: Redesign venting and gating to avoid trapped air pockets.
Process: Increase holding pressure; stabilize injection repeatability; replace worn plunger or shot sleeve.
Post-treatment: Apply vacuum impregnation to seal micro-porosity.
Verification: 100% leak testing for functional parts.
Appearance: Hard inclusions causing tool wear; surfaces appear with inconsistent brightness.
Detection: Machining observation or metallographic inspection.
Solutions:
Prevention: Avoid scooping oxide skin into ladles; remove crucible oxides; use clean tools; keep feedstock pure.
Verification: Monitor cutting tool wear; metallography to locate inclusions.
Appearance: Hard crystalline particles from primary silicon or Fe-Mn compounds.
Detection: Microscopic examination.
Solutions:
Materials: Do not add silicon powder directly; use master alloys; control Fe and Mn levels; increase melt temperature for full dissolution.
Verification: Grain size and silicon particle evaluation under microscope.
Appearance: Visible or subsurface cracks, easily propagate under load.
Detection: Visual, dye penetrant, or magnetic particle inspection.
Solutions:
Mold/Design: Add fillets, optimize draft angle, reduce wall thickness variation; improve cooling channels at hot spots; distribute ejector force evenly.
Process: Control mold temperature and cooling rate; delay ejection.
Materials: Adjust alloy composition (e.g., reduce Mg, increase Si for toughness).
Verification: Perform thermal cycling and fatigue tests.
Appearance: Smooth depressions, often in thick-wall areas.
Detection: Surface profile measurement.
Solutions:
Mold/Design: Keep uniform wall thickness; enhance localized cooling; optimize venting.
Process: Increase holding pressure and time; balance cooling rate.
Verification: Use CMM and surface profilometer to detect sink depth.
Appearance: Porous or spongy internal structure.
Detection: Radiography or density check.
Solutions:
Mold/Design: Redesign gates to transfer pressure effectively; strengthen cooling in heavy sections.
Process: Raise intensification pressure; reduce pouring temperature.
Verification: Density, porosity, and air-tightness testing.
Appearance: Gray or black film-like inclusions inside the casting.
Detection: Machining or metallographic sectioning.
Solutions:
Melting/Pouring: Skim slag carefully; avoid turbulence during pouring; protect melt surface from oxidation.
Process: Optimize filling velocity; add overflow wells to capture oxides.
Verification: Metallographic inspection, machining surface monitoring.
Appearance: Cracks at wall thickness transitions or hot spots caused by uneven cooling.
Detection: Visual inspection or functional testing.
Solutions:
Mold/Design: Reduce abrupt wall thickness changes; add cooling to hot spots; design smooth transitions.
Process: Control cooling gradient and holding pressure; delay mold opening.
Verification: Thermal cycle and stress testing.
Most defects in aluminum die casting and zinc die casting parts are linked to mold design, process parameters, material quality, and operational control. To minimize aluminum die casting defects, manufacturers should start by improving alloy cleanliness and melting practice, then focus on robust mold design, balanced thermal control, and optimized injection parameters.
For companies seeking long-term quality assurance, partnering with an experienced aluminum die casting factory ensures defect prevention from the source and guarantees reliable, consistent production.
EDT Diecasting Technology (Suzhou) Co., Ltd., as a professional aluminum die casting manufacturer, brings advanced European die casting technology to China. We are committed to providing customers with high-quality die cast parts. Equipped with state-of-the-art melting, casting, and inspection facilities, we strictly control every production stage to ensure consistent product quality. Whether for complex structural components or high-precision housings, we deliver reliable solutions through scientific processes and rigorous standards.
Choose EDT, choose quality and trust!
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0512-67371602
E-mail：sales@edt-china.cn
Add：West Building, 66 Songshan Road, Suzhou New District, P.R. China
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