Yang Yaqin, Mu Chongli, Han Zhongjian, Xu Jian, Li Baocheng
College of Materials Science and Engineering, North University of China, Taiyuan 030051, China.
Materials (Basel). 2020 Dec 24;14(1):36. doi: 10.3390/ma14010036.
The low plasticity of high strength Mg-Gd-Y alloy has become the main obstacle to its application in engineering. In this paper, the origin, propagation and fracture processes of cracks of a solution of treated Mg-13Gd-5Y-3Zn-0.3Zr alloy were observed and studied with scanning electron microscopy (SEM) in an in situ tensile test to provide theoretical references for the development of a new high-performance Mg-Gd-Y alloy. The results showed that there was still some bulk long period stacking order (LPSO) phase remaining in solid solution Mg-13Gd-5Y-3Zn-0.3Zr alloy. Most importantly, it was found that the locations of micro-cracks vary with the different solution treatment processes, mainly including the following three types. (1) At 480 × 10 h and 510 °C × 10 h, much bulk LPSO phase with higher elastic modulus remains in the alloy, which can lead to micro-cracks in the LPSO phase due to stress concentration. (2) At 510 °C × 13 h and 510 °C × 16 h, the phase structure of bulk LPSO changes, and the stress concentration easily appears at the LPSO/α-Mg interface, which leads to micro-cracks at the interface. (3) At 510 °C × 19 h and 510 °C × 22 h, the grain size increases, and the stress concentration is obvious at the grain boundary of coarse grains, which leads to the formation of micro-cracks.
高强度Mg-Gd-Y合金的低塑性已成为其在工程应用中的主要障碍。本文通过原位拉伸试验，利用扫描电子显微镜（SEM）对固溶处理后的Mg-13Gd-5Y-3Zn-0.3Zr合金裂纹的产生、扩展及断裂过程进行了观察和研究，为新型高性能Mg-Gd-Y合金的开发提供理论参考。结果表明，固溶态Mg-13Gd-5Y-3Zn-0.3Zr合金中仍残留有一定量的块状长周期堆垛有序（LPSO）相。最重要的是，发现微裂纹的位置随固溶处理工艺的不同而变化，主要包括以下三种类型。（1）在480℃×10 h和510℃×10 h时，合金中残留有较多弹性模量较高的块状LPSO相，因应力集中会导致LPSO相中产生微裂纹。（2）在510℃×13 h和510℃×16 h时，块状LPSO相的相结构发生变化，应力集中容易出现在LPSO/α-Mg界面处，导致界面处产生微裂纹。（3）在510℃×19 h和510℃×22 h时，晶粒尺寸增大，粗晶晶界处应力集中明显，导致微裂纹形成。
