Metal Casting Zone

Hello guys i am daniel from China, glad to find a society that love metal casting here
^0^.

I have just started on alluminium casting not long ago, have been trying to cast an alluminium cup/cyllinder, as it is shown below.

however i have been experiencing a lot of porosity problems, as it is shown in picture above. Porosity 1 is pinhole porosities which is small in size but always appears in large amount of number. Porosity 2 is a bigger hole which is clearly visible.

These porosities appear in my casting most of the time and only visible after the surface is machined. Can anyone help me to analyse what cause these porosities? and what is the possible option to ekiminate them. Really appriciate the help that will be offered. Cheers

Sounds like you have some gas bubbles in the Aluminum. You could try letting the melt sit for a few minutes before you pour. As long as it doesn't cool down too much. Or you can stir it with Argon or maybe Nitrogen. Just a couple thoughts.
Welcome to the forum.

i get that type of thing when i try and cast straight from scrap instead of pigging first.