热循环作用下2A12铝合金的微观结构与性能

摘要

The fatigue damage mechanisms of metal material under the satellite operation condition of low earth orbit environment were investigated. Optical microscopy, X­ray diffraction (XRD), transmission electron microscopy (TEM) and microhardness tester were used to investigate the evolution behavior of microstructures and properties of 2A12 aluminum alloy under various thermal cycles. The results indicate that the hardness decreases a little within 200 cycles, and the cyclic hardening phenomenon appears in the 200−300 cycles. After 300 cycles, the hardness of sample decreases evidently, the cyclic softening phenomenon turns up. The changes of performances of 2A12 aluminum alloy during the thermocycling process are closely related to the microstructural evolution. There are a lot of needle­like S′ phases (Al2CuMg) with small sizes in the samples after 300 thermal cycles. Up to 500 cycles, the S′ phases disappear, and bulky S phases (Al2CuMg) form. In addition, a large number of the cavities appear near the precipitates. The cavities are likely to become the favorable positions for the initiation of fatigue cracks.%　　为了考察低地球轨道卫星运行环境下金属材料的冷热疲劳损伤机制，采用模拟实验，并利用光学显微镜、XRD、TEM 及显微硬度仪分析研究热循环作用下2A12铝合金的微观结构和性能的演化行为。结果表明：在200次以内的热循环过程中，样品硬度有所降低；200~300次循环样品则出现循环硬化现象；300次循环后，样品硬度迅速下降，出现循环软化现象。微结构分析结果表明：热循环过程中，2A12铝合金的性能变化与其微观结构的演化行为关系密切，300次热循环时，样品中形成了大量尺寸细小的针状 S′相(Al2CuMg)；而500次循环样品中， S′相消失，代之以粗大 S 相(Al2CuMg)的形成。此外，500次热循环后，析出相附近区域形成大量的空穴，这些空穴容易成为冷热疲劳裂纹萌生的有利位置。