中文摘要：

利用光学显微镜、扫描电镜（SEM）、能谱分析（EDS）及X射线衍射分析对添加微量B和稀土元素Gd的AZ91镁合金的显微组织及相组成进行了研究,并对其室温力学性能进行了测试。结果表明,AZ91镁合金中添加Gd后,Gd与Al形成杆状或块状的Al2Gd化合物相。含Gd的质量分数为1.0%时,铸态合金的拉伸强度为207.8 MPa,相对未加Gd时提升了27.9%。AZ91镁合金复合添加B和Gd后,合金组织发生明显的变化,在减少Gd含量的基础上添加B,可达到用微量B代替部分Gd对AZ91的强化效果。对比单一添加Gd的铸态AZ91镁合金,在达到相同力学性能的情况下,（B＋Gd）复合微合金化的AZ91镁合金的Gd添加量质量分数降低了19%,从而降低了成本。

英文摘要：

The microstructure,phase composition of AZ91 magnesium alloy with trace amount of B and rare earth element Gd were investigated by using optical microscopy,scanning electron microscopy （SEM）,energy spectrum analysis （EDS） and X-ray diffraction （XRD） analysis.The effects of （B ＋ Gd） microalloying on the microstructure and mechanical properties of AZ91 magnesium alloys were studied at room temperature.The results showed that the rod or block Al2Gd phase was formed after adding the rare earth Gd into AZ91 magnesium alloy.When the content of Gd was 1.0%,the tensile strength of as-cast alloy was 207.8 Mpa which increased by 27.9% than that without Gd.After adding the combined （B ＋ Gd） into AZ91 magnesium alloy,the microstructure of alloy changed obviously.Based on reducing the content of Gd,the addition of trace amounts of B could achieve the strengthening effect of trace B instead of some Gd on AZ91.Compared with the as-cast AZ91 magnesium alloy with single addition of Gd,in the case of the same mechanical properties,the addition of Gd in the combined （B ＋ Gd） microalloying as-cast AZ91 magnesium alloy could save by 19%,which decreased the productive cost of alloys.