添加Sm对不同尺寸Mg-6Zn-0.4Zr镁合金坯料非枝晶组织演变的影响

采用半固态等温热处理法对添加0%、2%(质量分数)稀土SmΦ10mm和Φ20mm的Mg-6Zn-0.4Zr合金坯料非枝晶组织演变进行研究。结果表明,未添加Sm的两种尺寸合金坯料的半固态组织都存在明显的尺寸效应。从试样的边缘到芯部,固相颗粒尺寸由小逐渐变大,圆整度趋于恶化,液相逐渐减少;此外,随着坯料尺寸增大,由边缘到芯部的半固态组织的差异也增大。添加Sm的两种合金坯料经等温热处理后,固相颗粒的尺寸效应基本消除。固相颗粒尺寸整体变得均匀且细小,同时颗粒圆整度趋于完美,适宜触变成形要求。此外,添加2%的Sm使合金的非枝晶组织演变进程加快。

Study on the Non-dendritic Evolution of Multi-sized Mg-6Zn-0.4Zr Magnesium Alloy Initial Billet Caused by Sm Addition

The non-dendritic microstructure evolution of Mg-6Zn-0.4Zr alloy billet with the dimensions of Φ10 mm and Φ20 mm through the addition of 0wt%,2wt% rare earth Sm was investigated by semi-solid isothermal heat treatment.The obtained re-sults showed that the distinctly dimensional effect on microstructural evolution of the Sm-free alloy billet with diverse dimensions was observed,namely,the size of solid particles gradually increased,the particle roundness had a tendency to change deterioration,the liquid phase fraction gradually decreased from edge to center of the billets.Furthermore,with increasing diameter of the billet,the difference of semi-solid microstructures from edge to center for the billet further enlarged.For the Sm-containing alloy,after isother-mal heat treatment,the obviously dimensional effect on microstructural evolution of the alloy billet with mentioned two different si-zes was basically eliminated.The particle sizes of the whole zones from edge to center of the billets became more homogeneous and fi-ner,meanwhile,the roundness of particles tended to be perfect,and the non-dendritic microstructures satisfy thixoforming require-ment.In addition,the evolutional progress of non-dendritic microstructure was accelerated due to 2wt% Sm addition.