In　this　study,　the　modification　of　0.70　wt%　ScH3　alone　did　not　substantially　fine　the　grain　and　eliminate　the　hotcracking　of　Al-Mg-Sc　alloy,　resulting　in　low　strength　of　as-built　material.　In　contrast,　the　0.70　wt%　ScH3　and　0.34　wt%　ZrH2　modified　Al-Mg　alloy　(hereafter　denoted　as　Al-Mg-Sc-Zr1)　was　demonstrated　to　be　an　exceptionally　effective　inoculation　for　Al-Mg-Sc-Zr1　alloy,　owing　to　the　low　lattice　mismatch　(0.4　%)　between　Al3(Sc,Zr)　and　alpha-Al.　The　considerable　grain　refinement　was　ascribed　to　the　L12-Al3(Sc,Zr)　nucleis,　which　efficiently　promoted　heterogeneous　nucleants　of　alpha-Al　grains,　contributing　to　significant　refined　grain　size.　Consequently,　the　as-built　Al-Mg-Sc-Zr1　alloy　demonstrated　outstanding　tensile　strength　with　sound　elongation　to　fracture　due　to　crack-free　and　fine　grain　strengthening.　Additionally,　compared　with　Al-Mg-Sc-Zr1　alloy,　the　further　modification　with　more　ScH3　and　ZrH2　promoted　substantial　grain　refinement　via　inoculation　treatment　of　1.15　wt%　ScH3　+　0.55　wt%　ZrH2.　Moreover,　the　grain　refinement　effect　of　ScH3　and　TiH2　modification　was　also　studied　and　correlated　to　the　resulted　ultrafine　equiaxed　grains　and　performance.　These　results　indicate　that　grain　microstructure　and　mechanical　properties　of　as-built　Al　alloys　can　be　tailored　by　suitable　inoculants　which　can　be　further　employed　to　other　engineering　alloys.