The effect of the second-phase morphology on dynamic recrystallisation in a Mg–9Gd–0.8Al alloy during hot extrusion was investigated at a temperature of 400 ℃. Microstructure analysis of the as-cast Mg–9Gd–0.8Al alloy revealed a predominant composition comprising an α-Mg matrix, a petal-like (Mg,Al)₃Gd phase, and a lamellar Mg₅Gd phase along the grain boundary, along with a small proportion of a square Al₂Gd phase within the grain. Upon subjecting the alloy to a solid-solution treatment at 540 ℃, the lamellar phase underwent precipitation, eventually dissolving into the matrix as the treatment time increased. The recrystallisation volume fraction of the alloy showed a positive correlation with the solution time following hot extrusion at 400 ℃. The mechanical properties of the extruded alloy were tested, and the results revealed that the as-cast extruded alloy had the highest tensile strength of 317 MPa among the tested samples, mainly owing to its bimodal structure. Moreover, the broken (Mg,Al)₃Gd phase initiated particle-stimulated nucleation. Here, the extruded alloy subjected to 10 h of solution treatment exhibited the highest yield strength of 240 MPa. The increased yield strength was attributed to the presence of the broken (Mg,Al)₃Gd phase and the dispersion of lamellar (Mg,Al)₂Gd phases at the recrystallised grain boundaries. Notably, the alloy extruded with a treated solution for 50 h exhibited the most favourable plasticity compared to the others, achieving an elongation of 29.7%. These results underscore the significance of the study in understanding the relationship between the second-phase morphology and alloy behaviour after hot extrusion.

Graphical Abstract

中文翻译：

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挤压 Mg-Gd-Al 合金的显微组织和力学性能：挤压前初始第二相形貌的影响

研究了 400 ℃ 热挤压过程中第二相形态对 Mg-9Gd-0.8Al 合金动态再结晶的影响。铸态 Mg-9Gd-0.8Al 合金的显微组织分析表明，主要成分包括 α-Mg 基体、花瓣状 (Mg,Al) ₃ Gd 相和沿晶界的层状 Mg ₅ Gd 相，以及晶粒内一小部分方形 Al ₂ Gd 相。合金在540 ℃进行固溶处理后，随着处理时间的增加，层状相发生析出，最终溶解到基体中。合金的再结晶体积分数与400 ℃热挤压后的固溶时间呈正相关。对挤压合金的力学性能进行了测试，结果表明，铸态挤压合金在测试样品中具有最高的拉伸强度，为 317 MPa，这主要是由于其双峰结构。此外，破碎的 (Mg,Al) ₃ Gd 相引发了粒子刺激成核。在此，经过10小时固溶处理的挤压合金表现出最高的屈服强度，为240 MPa。屈服强度的增加归因于破碎的(Mg,Al) _{3 Gd 相的存在以及再结晶晶界处层状(Mg,Al) 2} Gd 相的分散。值得注意的是，与其他合金相比，用处理溶液挤压 50 小时的合金表现出最有利的塑性，达到 29.7% 的伸长率。这些结果强调了该研究对于理解热挤压后第二相形态与合金行为之间的关系的重要性。

图形概要