A fading mechanism during casting of treated Al-B-Sr master alloys in an aluminium-silicon cast alloy was investigated. Two different master alloys, the Al-3%B-3%Sr and Al-4%B-1%Sr were demonstrated for the efficiency test both grain refinement and modification microstructure. From experimental result, the addition of Al-3%B-3%Sr master alloy led to a refined grain size and fully modified eutectic Si. However, smaller grain sizes were found with Al-4%B-1%Sr master alloy addition while eutectic Si had coarser acicular morphology. The formation of high amounts of SrB6 compound in the Al-3%B-3%Sr master alloy resulted to increase of grain size and eutectic Si. In fading mechanism test when holding the melt for prolong time, the agglomeration of the SrB6 and AlSiSr compounds at the bottom of the casting specimen was important factors that decreased both grain refinement and modification efficiency. The stirring of the melt before pouring was found that the grain size and Si morphology were improved.