(1) the content of iron in alloy is too high or the content of silicon is too low;
(2) the content of harmful impurities in the alloy is too high, which reduces the plasticity of the alloy;
(3) Al Si alloy: aluminum silicon copper alloy containing zinc or copper content is too high, aluminum magnesium alloy contains too much magnesium;
(4) die, especially core temperature is too low;
(5) the wall thickness of casting varies violently;
(6) die leaving time is too long;
(7) force is unequal when ejection.