Mg-Bi合金热变形行为研究

Research on Thermal Deformation Behavior of Mg-Bi Alloys

摘要:

聚焦Mg-3Bi和Mg-6Bi 2种合金在400 ℃、应变速率0.001 s^-1 条件下的挤压变形行为，并深入剖析挤压过程中合金的微观组织特征。研究发现，当Bi含量由3wt%增加到6wt%，合金塑性显著提升，断后伸长率由2.1%增加到5.6%，抗拉强度由188.2 MPa提高到209.2 MPa。高温挤压变形时，Mg-3Bi合金的软化机制主要是不连续动态再结晶，Mg-6Bi合金的是不连续动态再结晶和粒子诱导再结晶，其中前者的晶粒尺寸要大于后者。对Mg-Bi合金采用模具挤压时，模具边缘区域应变明显大于中心区域，形成类似于等通道转角挤压变形织构，当变形量累积到一定程度后，粒子诱导再结晶机制启动。合金挤压变形后，模具边缘区域和中心区域的晶粒均呈现高度再结晶状态，晶粒c轴垂直于挤压方向，形成典型挤压纤维织构。对Mg-Bi合金力学性能提升的贡献从高到低依次为晶粒细化、位错强化和纳米相强化机制。较Mg-3Bi合金，Mg-6Bi的韧窝密度更大，分散了应力集中，因此表现出更好的塑性。

Abstract:

The extrusion deformation behavior of Mg-3Bi and Mg-6Bi alloys at 400 ℃ and a strain rate of 0.001 s^-1 was investigated, and the microstructure characteristics during extrusion were analyzed. Results show that as the Bi content increases from 3wt% to 6wt%, the plasticity of the alloy significantly improves, with the elongation increasing from 2.1% to 5.6%, and the tensile strength increasing from 188.2 MPa to 209.2 MPa. During high temperature extrusion deformation, the dominant softening mechanism of the Mg-3Bi alloy is discontinuous dynamic recrystallization (DDRX), whereas that of the Mg-6Bi alloy involves both DDRX and particle-stimulated nucleation (PSN). In this process, the grain size resulting from DDRX is larger than that produced by PSN. When Mg-Bi alloys are extruded through the die, the strain in the edge region of the die is significantly greater than that in the central region, consequently forming a deformation texture similar to that produced by equal-channel angular pressing (ECAP). Once the accumulated strain reaches a critical value, PSN is initiated. After extrusion deformation, the grains in both edge and central regions of the die exhibit a high degree of recrystallization, with their c-axes perpendicular to the extrusion direction, forming a typical extrusion fiber texture. The ranked contributions to the improvement of mechanical properties of Mg-Bi alloys, in descending order, are grain refinement, dislocation strengthening and nano-phase strengthening mechanisms. Compared with the Mg-3Bi alloy, the dimple density of Mg-6Bi alloy is higher, which disperses stress concentration and consequently enhances plasticity.