AZ31镁合金微结构关联的孪生形核与长大统计分析

A Statistical Analysis on Twin Nucleation and Growth Related to Microstructure of AZ31 Mg Alloy

为了揭示金属镁合金晶粒大小、晶向及晶界倾角等微结构与孪生形核及长大之间的关联性,通过EBSD技术获取大量诸如晶粒尺寸、晶向及晶界倾角等微结构以及晶内孪生形核数、孪晶厚度等数据进行统计分析。对应变为4.9%的镁合金微结构的统计分析表明:晶粒大小、晶界倾角等微结构分布基本符合概率函数Weibull分布特征;大晶粒、高Schmid因子、小角度晶界有利于孪生形核,而孪晶长大对微结构的敏感度较弱;不是所有高Schmid因子的孪生变体都能够形核长大。由对孪生形核与长大随应变递增的演化分析结果可推测:相同晶粒内,不同位置对孪晶变体的形核强度有显著影响,很显然存在其他晶内微结构如缺陷、位错密度等对孪生形核产生重要影响;然而孪晶长大更多地受到晶内存在的孪生形核数和孪晶变体类型数量的强烈影响。本工作可为发展孪生形核长大与微结构的数学关系提供试验依据。

The present work aimed to extract the relationships between twin nucleation and growth and material microstructure in magnesium,and conducted a statistical analysis on EBSD-obtained numerous crystallographic test data such as grain size,crystal orientation,grain boundary misorientation and twin number,twin thick generated by electron backscattering diffraction(EBSD)technique.The statistical analysis of microstructure at a strain of 4.9%indicates that the distribution characteristics of grain size,grain boundary misorientation follow basically a Weibull distribution,and that large grains,high Schmid factors and low-angle grain boundaries are conducive to twin nucleation,but twin growth shows relatively low sensitiveness towards the above microstructure.But not all twin variants with high twin Schmid factors can nucleate and grow.The analyses of twin nucleation and growth at varying true strains also indicate that the intensities of twin variants nucleation at different position are inconsistent in the same grain due to other factors,such as defects,and dislocation,etc.,that deeply influence twin nucleation.And on the other side,the twin growth rate strongly depends simultaneously on the number of twin nucleation and the number of twin variants.This work will provide a test basis for the exploration of mathematical relations between microstructure and twin nucleation&growth for Mg alloys.