The present paper investigates the variability in the static and cyclic properties of two nominally identical supplies of the aeronautical Al grade 7075-T6. Samples were extracted from extruded bars of 15 and 60 mm diameter and with slightly different chemical composition. Noticeable differences were found in tensile strength, total elongation, and low- and high-cycle fatigue strength, despite the nearly identical hardness value. The diverse mechanical behavior has been imputed to different extrusion ratio and therefore work hardening along with a more or less fine distribution of precipitates and dispersoids. The high-cycle fatigue strength was found to be in direct correlation with the monotonic yield strength and the size of the largest intermetallic precipitate. A simple equation based on Murakami sqrt (area) parameter is proposed to predict the fatigue endurance. Tensile tests and microstructural analyses are recommended instead of conventional hardness tests to have a tighter quality control on the mechanical properties of semifinished products.

中文翻译：

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挤压7075-T6铝合金静态和循环力学性能的变化

本论文研究了两种名义上相同的航空铝牌号 7075-T6 的静态和循环特性的可变性。从直径为 15 和 60 毫米且化学成分略有不同的挤压棒中提取样品。尽管硬度值几乎相同，但在拉伸强度、总伸长率以及低周和高周疲劳强度方面发现了显着差异。不同的机械行为归因于不同的挤出比，因此加工硬化以及沉淀物和分散体的或多或少的精细分布。发现高周疲劳强度与单调屈服强度和最大金属间化合物析出物的尺寸直接相关。提出了一个基于 Murakami sqrt（面积）参数的简单方程来预测疲劳耐力。建议使用拉伸测试和微观结构分析代替传统的硬度测试，以对半成品的机械性能进行更严格的质量控制。