Porosity in Al Cast
Porosity in Al Cast
(OP)
I would really need some help here about porosity.
I've recently joined a company which manufactures brake/clutch masters for automobiles which use AL alloy and through gravity die cast. since that it is a relatively med-small type of factory, we only use fluxing and grain refinement for the melt, and the cast products have always maintain quite a high efficiency, 80%. But for the past few month, efficiency has dropped to 60-40%, and that is way too low. Most of it is cause by porosity, both at internal and on the surface of the cast.
Will there be an alternative other than de-gassing to solve this?
Could the shrinkage of the cast which causes pressure change/variation be the cause of porosity?
Should we reduce the pouring/mould temp?
The pouring temp is about 700 Deg C, and mould temp 500 Deg C. The Alloy is grade AC2B.
Thanks.
I've recently joined a company which manufactures brake/clutch masters for automobiles which use AL alloy and through gravity die cast. since that it is a relatively med-small type of factory, we only use fluxing and grain refinement for the melt, and the cast products have always maintain quite a high efficiency, 80%. But for the past few month, efficiency has dropped to 60-40%, and that is way too low. Most of it is cause by porosity, both at internal and on the surface of the cast.
Will there be an alternative other than de-gassing to solve this?
Could the shrinkage of the cast which causes pressure change/variation be the cause of porosity?
Should we reduce the pouring/mould temp?
The pouring temp is about 700 Deg C, and mould temp 500 Deg C. The Alloy is grade AC2B.
Thanks.





RE: Porosity in Al Cast
Please also check the period or shift when the maximum rejection is occurring. There can be an error by the operator.
If you are close to Foseco representative, he can be helpful too.
RE: Porosity in Al Cast
There is a time-sampling inspection, but they usually don't get those with defects. It is only during subsequent mechining process could be found by visual inspection.
No degasser is used before pouring.
RE: Porosity in Al Cast
Perhaps your source of problem is the melting equipment itself. Please take adequate steps to degass the metal and pour.
You could build a small furnace using LPG as fuel and understand the benefits.
Can I ask as to where your foundry is located?
RE: Porosity in Al Cast
As for the shrinkage, it is probably due to a temperature difference between your mould and the melt or between two melt flows. A problem could be with your runners and gates. If they are not positioned at a proper location, there may be a temperature and flow difference between the metal that travels farther, ie. through useless runners or gates where it becomes "cold", and the "hot" metal that meets it. I had that problem, and all I had to do was move a runner about 0.5" to avoid shrinkage.
Coka
RE: Porosity in Al Cast
is suggest the following
1. ensure that the tools are kept warm and dry
2. ensure ambient conditions are warm, no doors open and no cold air coming in.
3. check gas levels prior to casting, we done this by machine, but a simple sample under vacuum will show if excess gas is present.
4. make sure returns being charged are warmed up, prior to charging into a pot in use (if done this way)