AZ91+0~2.0%La铸造镁合金的组织和力学性能

Microstructures and Mechanical Properties of As-Cast AZ91+0-2.0wt.%La Magnesium Alloys

摘要:

利用SEM和XRD等方法研究不同La添加量的AZ91+xLa（x=0%，0.3%，0.5%，0.7%，1.0%，1.5%，2.0%）（质量分数，下同）镁合金的铸态显微组织和相组成，并测试和分析合金的室温力学性能。结果表明：AZ91合金中加入0.3%~2.0%的La后，合金的晶界和枝晶界析出Al11La3化合物，其形态随La含量的增加从针状向片状过渡，同时β-Mg17Al12相的体积分数及尺寸随La加入量的增加而减小。此外，La的加入可明显细化AZ91合金的显微组织，其最佳加入量为1.0%~1.5%。稀土La的加入可以明显改善AZ91合金的力学性能，其原因与稀土细化组织、改变β-Mg17Al12相的体积分数及尺寸、弥散强化等有关。在本试验研究的合金中，AZ91+1.5%La合金力学性能最好，其铸态合金的抗拉强度和断裂延伸率分别达到226 MPa和7.5%。

Abstract:

The microstructures and phase composition of as-cast AZ91+xLa alloys (x=0%, 0.3%, 0.5%, 0.7%, 1.0%, 1.5% and 2.0%, mass fraction) were investigated by SEM and XRD, and their mechanical properties were tested at room temperature. When 0.3%-2.0% La was added into the AZ91 alloys, Al11La3 phase was precipitated along the grain boundaries and interdendritic boundaries, and its morphology changed from acicular to flake gradually as the La content was increased. Meanwhile the size and volume fraction of β-Mg17Al12 phase was decreased. Moreover, the grain sizes of α-Mg were greatly reduced with La addition, and the best refinement is obtained in alloys containing 1.0%-1.5% La. Mechanical properties of AZ91 magnesium alloy can be improved significantly by addition of La, which results from the fine-grain strengthening of La, the optimization of the morphology and amount of β-Mg17Al12 phase and dispersion strengthening etc. Among all the investigated alloys, the AZ91+1.5%La alloy exhibits the optimum mechanical properties, i.e. the ultimate tensile strength is 226 MPa and the elongation 7.5% at room temperature.