Aluminium self hardening alloy cast in sand

[Nadimuthu]

Dear all,
We are using AlZn10Si8Mg alloy as per previous DIN1725 standard for our customers.
This alloy is not prescribed in the new EN1706 1998 standard but our customers still want it.
The problem is the yield of castings for this particular alloy is very low.
Also in the case of AlSi12(LM6) we find that castings cast in sand have a lot of shrinkage defects while the same comes out well in AlSi7Mg.
Any help in these aspects is most welcome.

 

[etch]

The first part i cannot help with, but the second i can maybe offer some insight.

Alloys with higher silicon content tend to have higher shrinkage. one way to combat this it to shift te eutectic of the alloy to the right, thus allowing a longer freezing range. there are two ways to do this, one is sodium, which works well but is difficult to control the other is strontium, which is easier to add but its effects do not seem to be as good.

I have used both, usually strontium on thinner sections and sodium for thicker casting and obtained favourable results for both, let me know how you got on, in adddition, a small amout of grain refining to reduce the needle like structre of the silicon might help some feeding characteristics.