The invention discloses an aluminum-
silicon-
magnesium casting alloy mechanical property improving method. Light
rare earth is adopted and cooperates with heavy
rare earth to process
alloy melt, and the
iron content is 0.09-0.20 wt% of the
alloy melt
mass. According to the improving method, based on the difference, in the aspect of physicochemical property, between light
rare earth elements and heavy rare earth elements as well as the influence on the alloy
crystallization process, the method of utilizing the light rare earth and the heavy rare earth to be combined and modified to control the
microstructure and
mechanical property of alloy is provided, the light rare earth and the heavy rare earth give play to
advantage separately, namely, the light rare earth is focused on enriching on thealpha-Al and Si
crystal solidification front and being adsorbed on the surface of
crystal, and achieves the effects of refining and modifying; and the heavy rare earth is focused on adsorbing or conducting
solid solution on iron-rich Al-Fe and Al-Fe-Si group harmful compound, influencing the
microstructure of the compound, impeding growth of
crystal, and promoting the compound to be decomposed into short rod-like shape or granular shape at the high temperature; and the light rare earth and the heavy rare earth achieve mutual complementarity in the aspect of controlling the
microstructure of the alloy, and substantially, the quite good modifying effect is achieved.