Appearance:

The pores, which appear predominantly after polishing have a typical form of such “crows feet” like appearance and its appearance is sometimes very similar to the shrinkage porosity. The mechanical strength of the cast can be affected and embrittlement usually occurs.

Caused by:

Solved by:

The melt must be protected from oxygen by covering with protective gas (e.g. nitrogen or argon).
The recycled material must be thoroughly cleaned to remove the oxide by pickling in dilute sulfuric acid prior to recycling.
The ratio of recycled materials which contain high zinc content must be kept as low as possible during recycling. It can avoid the presence of excessive zinc oxide.
Casts with serious oxide inclusion porosity should be subjected to refining instead of further recycling.

S-530