The inhomogeneity of friction stir weld (FSW) joint of a 7085 Al‐based alloy containing trace Sc was investigated by comparing the hardening phase morphology, grain structure, mechanical properties, and fatigue crack growth (FCG) behavior in based metal (BM), heat‐affected zone (HAZ), and weld nugget zone (WNZ). The results showed that microstructural evolution during FSW was remarkably affected by Sc addition. The recrystallization and growth of grains in BM and HAZ were restrained by coherent Al₃(Sc,Zr) particles. In HAZ, partially dissolution and slight growth of precipitates resulted in softening but contributed to enhance the FCG resistance according to shear mechanism. In WNZ, high frictional heating and intense plastic deformation induced recrystallization and supersaturated solid solution which decomposed to form new reprecipitates, including many new GPII zones, η′ phases, and some coarse η equilibrium phases attached to grown incoherent Al₃(Sc,Zr). Owing to combined influences of fine random orientated grain structure and reprecipitates, WNZ possessed the best fatigue endurance.

中文翻译：

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微量Sc添加7085合金搅拌摩擦焊接头的组织和疲劳裂纹扩展行为的不均匀性。

通过比较基体金属（BM）中的硬化相形态，晶粒结构，力学性能和疲劳裂纹扩展（FCG）行为，研究了含有痕量Sc的7085 Al基合金的搅拌摩擦焊（FSW）接头的不均匀性，热影响区（HAZ）和熔核区（WNZ）。结果表明，添加Sc对FSW过程中的微结构演变有显着影响。相干Al ₃抑制了BM和HAZ中晶粒的再结晶和生长。（Sc，Zr）颗粒。在热影响区中，部分溶解和沉淀物的少量生长导致软化，但根据剪切机理有助于增强FCG抵抗力。在WNZ中，高摩擦加热和强烈的塑性变形导致了再结晶和过饱和固溶体的分解，形成了新的再沉淀物，包括许多新的GPII区，η ′相和一些附着在生长的非相干Al ₃（Sc，Zr）上的较粗的η平衡相。。由于细小无规取向的晶粒结构和析出物的综合影响，WNZ具有最佳的疲劳强度。