Gu Guochao, Li Ruifen, Xiang Lixin, Xiao Guiyong, Lu Yupeng
Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061, China.
School of Materials Science and Engineering, Shandong University, Jinan 250061, China.
Materials (Basel). 2023 Sep 10;16(18):6145. doi: 10.3390/ma16186145.
The non-dendritic microstructure plays a crucial role in determining the rheological properties of semi-solid alloys, which are of the utmost importance for the successful industrial application of the thixoforging process. To further understand the impact of the reheating process on the evolution of microstructure and thixotropic deformation behavior in the semi-solid state, a hot extruded and T6 treated 7075 aluminum alloy was reheated to the selected temperature ranges using varying heating rates. Subsequently, thixo-compression tests were performed. The study found that during reheating and isothermal holding, the elongated microstructure of the as-supplied alloy can transform into equiaxed or spherical grains. The presence of recrystallized grains was found to be closely linked to the penetration of the liquid phase into the recrystallized grain boundaries. Furthermore, it was observed that higher heating rates resulted in smaller grain sizes. The thixotropic flow behavior of the alloy with various microstructures was analyzed using the true stress-strain curves obtained by thixo-compression experiments, which exhibited three stages: a rapid increase in true stress to a peak value, followed by a decrease in true stress and a steady stress until the end of compression. The stress fluctuated with strain during the formation of the slurry at a strain rate of 10 s, indicating the significant role of strain rate in material flow during semisolid formation.
非枝晶微观结构在决定半固态合金的流变性能方面起着关键作用，这对于触变锻造工艺的成功工业应用至关重要。为了进一步了解再加热过程对半固态微观结构演变和触变变形行为的影响，采用不同的加热速率将热挤压并经T6处理的7075铝合金再加热到选定的温度范围。随后，进行了触变压缩试验。研究发现，在再加热和等温保持过程中，供应态合金的拉长微观结构可转变为等轴或球形晶粒。发现再结晶晶粒的存在与液相渗入再结晶晶界密切相关。此外，观察到较高的加热速率导致较小的晶粒尺寸。利用触变压缩实验获得的真应力-应变曲线分析了具有不同微观结构的合金的触变流动行为，该曲线呈现三个阶段：真应力迅速增加到峰值，随后真应力下降并保持稳定直至压缩结束。在应变速率为10 s时形成浆料的过程中，应力随应变波动，表明应变速率在半固态形成过程中材料流动中起重要作用。
