Investigation on the modification behavior of A356 alloy inoculated with a Sr-Y composite modifier  

作　　者：董允 郑润国 林小娉 叶杰 孙岭 

机构地区：[1]School of Materials and Metallurgy,Northeast University [2]BERIS Engineering and Research Corporation QHD branch

出　　处：《Journal of Rare Earths》2013年第2期204-208,共5页稀土学报（英文版）

基　　金：Project supported by National Natural Science Foundation of China(51141007)

摘　　要：In the present paper, differential scanning calorimetry （DSC）, scanning electron microscopy （SEM）, and X-ray diffraction （XRD） were used to examine the effects of a Sr-Y composite modifier on the microstructure of A356 alloy. After adding Y to A356, YAl 3 compounds formed, and the size of the α （Al） crystal nucleus increased. The degree of supercooling caused by Sr-Y composite modifier was higher than Sr modification by 2.7 °C, leading to an increased nucleation rate. This increase in supercooling temperature was favorable to the refinement of eutectic structure of the alloy and its eutectic reaction was delayed to the maximum extent. The Si phase in the as-cast Sr-Y composite-modified A356 alloy was either granular or flaky. No large flakes of eutectic Si were found, and the modification effects were completely comparable with those obtained using a lone Sr modifier. After T6 heat treatment, most of the eutectic Si showed a grain-like shape with smaller grains. No eutectic Si with long-strip shapes, significant enhancements in the particle roundness and evenness of the Si crystals, and increased globosity were observed. Both the roundness and evenness of the grained Si crystals were enhanced, and the amount of globular eutectic Si available increased, these findings showed that excellent modification effects were achieved.In the present paper, differential scanning calorimetry （DSC）, scanning electron microscopy （SEM）, and X-ray diffraction （XRD） were used to examine the effects of a Sr-Y composite modifier on the microstructure of A356 alloy. After adding Y to A356, YAl 3 compounds formed, and the size of the α （Al） crystal nucleus increased. The degree of supercooling caused by Sr-Y composite modifier was higher than Sr modification by 2.7 °C, leading to an increased nucleation rate. This increase in supercooling temperature was favorable to the refinement of eutectic structure of the alloy and its eutectic reaction was delayed to the maximum extent. The Si phase in the as-cast Sr-Y composite-modified A356 alloy was either granular or flaky. No large flakes of eutectic Si were found, and the modification effects were completely comparable with those obtained using a lone Sr modifier. After T6 heat treatment, most of the eutectic Si showed a grain-like shape with smaller grains. No eutectic Si with long-strip shapes, significant enhancements in the particle roundness and evenness of the Si crystals, and increased globosity were observed. Both the roundness and evenness of the grained Si crystals were enhanced, and the amount of globular eutectic Si available increased, these findings showed that excellent modification effects were achieved.

关 键 词：eutectic Si composite modifier degree of supercooling rare earths 

分 类 号：TG146.21[一般工业技术—材料科学与工程] TS426[金属学及工艺—金属材料]