Effects of Re modification and Sr modification on constituent and morphology of surface oxidized film of A356 aluminum alloy have been observed by X-ray and SEM.The influential mechanism of Re modification and Sr modification on hydrogen content in A356 melt has been understood from view of compactness and completeness of surface oxidized film.The results indicate that compound LaAl

11O

18 was formed on surface oxidized film on Re modified A356 alloy

which makes surface oxidized film more compact and very flat with almost no-crack defects to effectively prevent reaction of Al from water.While a large number of compound SrAl

2

O

4

was formed on the surface oxidized film of Sr modified alloy

which deteriorates the compaction of surface oxidized film to generate amounts of track from crack in the surface oxidized film to greatly promote the reaction between Al and water due to the fresh liquid Al continuously exploding over air

resulting in the sharp increase of hydrogen content in the melt.