基于分形维数的立式连续铸造Cu-15Ni-8Sn合金铸锭偏析特征

Segregation characteristic of vertical continuous casting Cu-15Ni-8Sn alloy ingot based on fractal dimension

本文采用立式连续铸造制备直径160 mm的Cu-15Ni-8Sn合金铸锭,并基于分形维数对Cu-15Ni-8Sn合金中组织非均匀性进行了探究。结果表明:Cu-15Ni-8Sn合金的微观组织由树枝晶组织和偏析组织构成,树枝晶组织分形维数可以作为衡量微观组织非均匀性的重要指标。浇铸温度为1280℃时,随着树枝晶组织分形维数的增加(1.77~1.82),偏析率从32%降低至12.5%。与此同时,大偏析点逐渐向小偏析点转变,Ⅰ类偏析点面积占比从60%下降至10%,Ⅱ类偏析点面积占比从35%上升到80%;相对于二次枝晶间距,分形维数弥补了二次枝晶间距在描述Cu-15Ni-8Sn合金树枝晶组织形貌特征上的局限性。此外,树枝晶组织的分形维数与偏析组织的分形维数在一定程度上呈正相关关系。选择较低的浇铸温度有利于得到偏析率较低、组织分布更加均匀的铸锭。

In this work,Cu-15Ni-8Sn alloy ingot with diameter of 160mm was prepared by vertical continuous casting.Based on fractal dimension,the structure in homogeneity in Cu-15Ni-8Sn alloy was investigated.The results show that microstructure of Cu-15Ni-8Sn alloy consists of dendrite structure and segregation structure,and the fractal dimension of dendrite structure can be used as an important index to measure the microstructure in homogeneity.Under the pouring temperature of 1280℃,with the increase of fractal dimension of dendrite structure,the segregation rate decreases from 32%to 12.5%.At the same time,the area proportion of segregation pointⅠdecreases from 60%to 10%,and that of segregation pointⅡincreases from 35%to 80%,which indicates that large segregation points gradually change to small segregation points.Moreover,compared with the secondary dendrite spacing,the fractal dimension compensates for the limitation of secondary dendrite spacing in describing the dendrite morphology of Cu-15Ni-8Sn alloy.Additionally,the fractal dimension of dendrite structure and the fractal dimension of segregation structure are positively correlated.Under the pouring temperature of 1280℃,the fractal dimension of segregation structure increases from 1.15 to 1.45 with the increase of fractal dimension of dendrite structure.The lower pouring temperature is beneficial to obtain the ingot with lower segregation rate and more uniform microstructure distribution.