AN INVESTIGATION ON Sr MODIFICATION OF AN Al-Si-Cu-Mg ALLOY

The Sr modification of an Al-Si-Cu-Mg hypoeutectic cast alloy has been investigated by using SEM with both wavelength and energy dispersive X-ray spectrometers. It is found that the Sr addition does not affect the size of Al-Si eutectic cells in the alloy, but changes the morphology of eutectic Si. Hence, the Sr modification is resulted not by the change in nucleation of eutectic Si, but by that in mode of its growth. An available new idea "modification threshold value" was also proposed.