 When no porosity is allowed in a cast part then the pore @-@ free casting process is used . It is identical to the standard process except oxygen is injected into the die before each shot to purge any air from the mold cavity . This causes small dispersed oxides to form when the molten metal fills the die , which virtually eliminates gas porosity . An added advantage to this is greater strength . Unlike standard die castings , these castings can be heat treated and welded . This process can be performed on aluminium , zinc , and lead alloys . 
