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

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

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。

The non-dendritic microstructure evolution of Mg-6Zn-0.4Zr alloy billet with the dimensions ofΦ10 mm andΦ20 mm through the addition of 0wt%,2wt%rare earth Sm was investigated by semi-solid isothermal heat treatment.The obtained results 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 isothermal heat treatment,the obviously dimensional effect on microstructural evolution of the alloy billet with mentioned two different sizes was basically eliminated.The particle sizes of the whole zones from edge to center of the billets became more homogeneous and finer,meanwhile,the roundness of particles tended to be perfect,and the non-dendritic microstructures satisfy thixoforming requirement.In addition,the evolutional progress of non-dendritic microstructure was accelerated due to 2wt%Sm addition.