Quality
Die casting defects and how to fix them
Fourteen common aluminium die casting defects, what they look like, why they happen and the remedies that work, with a downloadable troubleshooting chart.
Most die casting defects come from four sources: the melt, the die, the shot and the handling after ejection. The table lists the common ones with what they look like, why they happen and how they are fixed.
Download the defects chart (PDF) →
Defects, causes and remedies
| Defect | What it looks like | Likely causes | Remedies |
|---|---|---|---|
| Gas porosity | Smooth, rounded holes, often near the surface or in last areas to fill | Air trapped during fill; hydrogen in the melt; steam from excess die spray | Optimise slow shot and venting; add overflows; degas and check density index; reduce spray; consider vacuum |
| Shrinkage porosity | Irregular, jagged voids in thick sections | Thick sections not fed; low intensification; hot spots | Uniform walls; intensification and squeeze pins; local cooling; review gate position |
| Cold shut | Visible line where two metal fronts met | Metal or die too cold; slow fill; long flow path | Raise die and metal temperature; increase fast shot speed; move gates; add overflows |
| Misrun | Incomplete casting, missing sections | Metal freezes before filling; insufficient shot weight | Increase metal and die temperature and fill speed; check shot weight and venting |
| Flash | Thin fins at parting line, slides or pins | Low clamping force; worn or dirty die faces; excess pressure | Clean and repair faces; check clamp tonnage; adjust intensification |
| Soldering | Aluminium stuck to die, torn surface | Die too hot; low iron in alloy; poor release agent; erosion | Control die temperature; correct alloy iron; improve spray; coat the area |
| Blisters | Raised bubbles, often after heating | Gas trapped just under the skin | Reduce trapped air and spray; avoid solution heat treatment of HPDC parts |
| Hot tear or crack | Ragged cracks at section changes | Restrained shrinkage; sharp corners; ejecting too early or too hot | Add radii; balance cooling; adjust dwell time; check ejection |
| Inclusions | Hard spots or oxide films on machined faces | Dross, oxides, sludge or refractory in the melt | Clean charge; gentle skimming; flux; control sludge factor; filter where possible |
| Sink marks | Shallow depressions over thick sections | Local shrinkage near the surface | Core out thick sections; improve feeding and cooling |
| Heat check marks | Raised network pattern on the surface | Cracked die surface from thermal fatigue | Repair and polish the die; preheat; stress relieve |
| Drag marks | Scratches along the direction of ejection | Insufficient draft; die damage; soldering | Increase draft; polish; improve spray |
| Distortion | Part out of flatness or position | Uneven cooling; early ejection; poor handling | Balance cooling; adjust dwell; fixtures for trimming and machining |
| Flow marks | Swirl or lines on the surface | Low die temperature; turbulent fill | Raise die temperature; adjust gate and fill speed |
A systematic approach
- Locate: section, X ray or CT the part to find where the defect sits.
- Classify: gas or shrinkage, oxide or sludge; the shape of the void tells you which.
- Correlate: compare with shot profiles, die temperatures and melt records for the same lot.
- Correct: change one variable at a time and verify on a controlled run.
- Lock in: update the control plan and process limits so it stays fixed.
Values are typical published ranges for guidance. Every part is different: process windows are set and proven for each component through trials, and the governing standard and your drawing take precedence. Reviewed by the Alcast engineering team, November 2026.
Questions engineers ask
How do you tell gas porosity from shrinkage porosity?
Gas pores are smooth and rounded. Shrinkage voids are irregular and jagged and sit in thick sections that solidify last.
What causes cold shuts in die casting?
Metal fronts that meet too cold to fuse, usually from low metal or die temperature, slow fill or a long flow path.
How do you reduce soldering?
Control die temperature, keep iron in the alloy within specification, use an effective release agent and coat or redesign areas where metal strikes the die.
Can porous castings be saved?
If porosity only causes leaks and the part is otherwise sound, vacuum impregnation can seal it. Structural porosity has to be fixed in the process.