在不同返回次数的母合金锭距离底部8mm的截面上观察夹杂物。先用400#砂纸进行粗磨，然后用800#、1200#和2000#砂纸逐级进行细磨，最后进行机械抛光。采用配有能谱仪的ZEISS Sigma 300场发射扫描电镜分析金相试样表面裸露的夹杂物的成分、尺寸和形貌。进一步地，采用自动SEM (ZEISS, EVO18)-EDS (Oxford Instrument, INCA)设备定量分析夹杂物的数量、尺寸和成分。氧化物最小尺寸设置为0.5μm。

2021Observe the inclusions on the cross-section 8mm from the bottom of the master alloy ingots with different return times. First, rough grinding is carried out with 400# sandpaper, then fine grinding is done step by step with 800#, 1200# and 2000# sandpapers, and finally mechanical polishing is performed. The composition, size and morphology of the exposed inclusions on the surface of the metallographic specimens were analyzed by using a ZEISS Sigma 300 field emission scanning electron microscope equipped with an energy spectrometer. Furthermore, the quantity, size and composition of inclusions were quantitatively analyzed by using the automatic SEM (ZEISS, EVO18)-EDS (Oxford Instrument, INCA) equipment. The minimum size of the oxide is set to 0.5μm.