Hydrogen absorption.
Dry everything by heating to hot before melting, this includes tools, crucibles, ingots - everything. Pour just as soon as the melting and degassing is finished, not 7-12 mins later. Consider using a cover flux while melting.
I used to degas by bubbling dry argon through the melt using a bit of 15 mm stainless steel pipe with the end sealed by flattening and a few 1 mm holes drilled in the sides.
Hydrogen from water in any form of moisture is highly soluble in molten aluminium. A humid day can give you issues.
Dry everything by heating to hot before melting, this includes tools, crucibles, ingots - everything. Pour just as soon as the melting and degassing is finished, not 7-12 mins later. Consider using a cover flux while melting.
I used to degas by bubbling dry argon through the melt using a bit of 15 mm stainless steel pipe with the end sealed by flattening and a few 1 mm holes drilled in the sides.
Hydrogen from water in any form of moisture is highly soluble in molten aluminium. A humid day can give you issues.
Andrew Mawson, proud to be a member of MetalworkingFun Forum since Oct 2013.