This study investigates the effect of characteristics and distribution of MgAl precipitates on the uniaxial tensile and three-point bending properties of extruded Mg alloys containing high Al contents. The extruded Mg–9Al–1Zn–0.3Mn (AZ91) alloy contains lamellar-structured MgAl discontinuous precipitates along the grain boundaries, which are formed via static precipitation during natural air cooling. The extruded Mg–11Al–1Zn–0.3Mn (AZ111) alloy contains spherical MgAl precipitates at the grain boundaries and inside the grains, which are formed via dynamic precipitation during extrusion. Due to inhomogeneous distribution of precipitates, the AZ111 alloy consists of two different precipitate regions: precipitate-rich region with numerous precipitates and finer grains and precipitate-scarce region with a few precipitates and coarser grains. The AZ111 alloy exhibits a higher tensile strength than the AZ91 alloy because its smaller grain size and more abundant precipitates result in stronger grain-boundary hardening and precipitation hardening effects, respectively. However, the tensile elongation of the AZ111 alloy is lower than that of the AZ91 alloy because the weak cohesion between the dynamic precipitates and the matrix facilitates the crack initiation and propagation. During bending, a macrocrack initiates on the outer surface of bending specimen in both alloys. The AZ111 alloy exhibits higher bending yield strength and lower failure bending strain than the AZ91 alloy. The bending specimens of the AZ91 alloy have similar bending formability, whereas those of the AZ111 alloy exhibit considerable differences in bending formability and crack propagation behavior, depending on the distribution and number density of precipitates in the specimen. In bending specimens of the AZ111 alloy, it is found that the failure bending strain (ε) is inversely proportional to the area fraction of precipitates in the outer zone of bending specimen (), with a relationship of ε = –0.1 + 5.86.

中文翻译：

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Mg17Al12析出相特征和分布对高Al镁合金拉伸和弯曲性能的影响

本研究研究了 MgAl 析出物的特性和分布对高 Al 含量挤压镁合金单轴拉伸和三点弯曲性能的影响。挤压的 Mg-9Al-1Zn-0.3Mn (AZ91) 合金沿晶界含有层状结构的 MgAl 不连续析出物，这些析出物是在自然空气冷却过程中通过静态析出形成的。挤压的 Mg-11Al-1Zn-0.3Mn (AZ111) 合金在晶界和晶粒内部含有球形 MgAl 析出物，这些析出物是挤压过程中动态析出形成的。由于析出物分布不均匀，AZ111合金由两个不同的析出区组成：析出物较多、晶粒较细的富析出区和析出物较少、晶粒较粗的贫析出区。AZ111合金比AZ91合金表现出更高的拉伸强度，因为其较小的晶粒尺寸和更丰富的析出物分别导致更强的晶界硬化和沉淀硬化效应。然而，AZ111合金的拉伸伸长率低于AZ91合金，因为动态析出物与基体之间的内聚力较弱，有利于裂纹的萌生和扩展。在弯曲过程中，两种合金的弯曲样品的外表面上都会出现宏观裂纹。与 AZ91 合金相比，AZ111 合金表现出更高的弯曲屈服强度和更低的失效弯曲应变。AZ91合金的弯曲试样具有相似的弯曲成形性，而AZ111合金的弯曲试样在弯曲成形性和裂纹扩展行为方面表现出相当大的差异，这取决于试样中析出物的分布和数量密度。在AZ111合金的弯曲试样中，发现失效弯曲应变(ε)与弯曲试样外层析出物的面积分数()成反比，关系为ε = –0.1 + 5.86。