Abstract A bimodal microstructure composed of large primary α-Al phases (PPs) and small secondarily solidified grains (SSGs) is fabricated in 6061 aluminum alloy by powder thixoforming (PTF) method after solution treatment. Artificial aging treatment introduces nanosized precipitates into the bimodal microstructure, in which the number and growth rate of precipitates are different: the number in PPs is larger than that in SSGs due to the higher density of dislocations and lattice distortions in PPs, while the growth rate in SSGs is higher than that in PPs owing to the higher solute concentration in SSGs. As the number and size of precipitates are optimized in the bimodal microstructure, i.e., in peak-aged state, remarkable increments of 56.1% and 130.3% in ultimate tensile strength and yield strength while a moderate increase of 6.3% in ductility are achieved compared with the as-fabricated state, which overcomes the trade-off in strength and ductility of conventional aging-treated 6061 alloys with unimodal microstructure. The strengthening comes from the geometrically necessary dislocations induced by the deformation incompatibility of bimodal microstructure and from precipitate strengthening by nanosized precipitates, while the toughening is from the enhanced dislocation accumulation in this alloy.

中文翻译：

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分散有纳米级析出物的双峰显微组织使铝合金具有大的延展性

摘要 通过固溶处理后的粉末触变成形(PTF) 方法在6061 铝合金中制备了由大的初生α-Al 相(PPs) 和小的二次凝固晶粒(SSGs) 组成的双峰显微组织。人工时效处理将纳米尺寸的析出物引入双峰显微组织中，其中析出物的数量和生长速度不同：PPs 中的数量比 SSGs 中的要多，因为 PPs 中的位错和晶格畸变密度较高，而生长速度由于 SSGs 中的溶质浓度较高，SSGs 中的 PPs 高于 PPs。由于析出物的数量和尺寸在双峰显微组织中进行了优化，即在峰值时效状态下，极限抗拉强度和屈服强度显着增加了 56.1% 和 130.3%，同时适度增加了 6。与制造状态相比，延展性提高了 3%，这克服了具有单峰显微组织的常规时效处理 6061 合金在强度和延展性方面的权衡。强化来自于双峰显微变形不相容引起的几何必要位错和纳米尺寸的沉淀强化，而增韧则来自该合金中增强的位错积累。