含1%混合稀土压铸镁合金的高周疲劳性能

High Cycle Fatigue Property of Die Casting Magnesium Alloy AZ91D Containing 1% Mischmetal

摘要:

研究含混合稀土1%(质量分数)的压铸镁合金AZ91D在应力比r=0.1的高周疲劳性能。组织分析表明，压铸镁合金试样的表面层和心部的显微组织存在差别。室温条件下抗拉强度为185 MPa，屈服强度为159 MPa，延伸率为1.5%。测试存活率p=50%的p-S-N曲线，结果显示在3.8×105循环周次时的疲劳强度为70 MPa，得出在循环周次103~106之间，p=50%时，S与Np的关系式为lgNp=17.85–6.83lgS。在较低的应力下，一些疲劳试样断口出现擦痕，当缺陷较小时，疲劳断口表现为韧窝、撕裂棱、疲劳条带等韧性断口和准解理的混合特征，属于具有较低韧性的材料。

Abstract:

The high cycle fatigue behavior of die casting magnesium alloy AZ91D containing 1% mischmetal (AZ91D-1%MM) at the stress ratio of 0.1 was investigated. The microstructure difference between the skin and the core region of the die casting specimen was analyzed using optical microscopy and XRD. The ultimate tensile strength, yield strength and elongation are 185 MPa, 159 MPa and 1.5% at room temperature, respectively. The p-S-N curve (p=50%) of the die casting AZ91D-1%MM is determined and the fatigue strength at 3.8×105 cycles is 70 MPa. A linear relation between S and Np in log scale between 103 and 106 cycles is given as lgNp=17.85–6.83lgS. The fracture surfaces of some fatigue specimens at lower stress exhibit rubbing mark. The fatigue fracture surface of specimens with minor defects possesses the mixed characteristics of quasi-cleavage and gliding fracture such as tearing ridge, dimple or fatigue striation; therefore, the material belongs to lower-ductility materials.