Unveiling the self-annealing phenomena and its effect on microstructure and texture evolution in the room temperature rolled Cu-0.13Sn-0.04Mg alloy

In this study, we investigated the microstructural evolution of a Cu-0.13Sn-0.04Mg alloy that underwent heat treatment followed by room temperature rolling (RTR). Initially heat-treated specimens were rolled at room temperature (RT) with reduction ratios (RR) of 40% and 75% to perform microstructural and crystallographic textural analyses. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were utilise to examine both initial and deformed microstructures. Both exhibited heterogeneous microstructural distributions. Shear bands (SBs) existed in the initial specimen and became main sites for the nucleation of new grains during heat treatment. A denser presence of SBs was noted in the RTR specimens. Remarkably, an unusual self-annealing phenomenon was observed in these specimens, culminating in the emergence of recrystallized grains at RT. A plethora of such grains was observed in the severely deformed specimens, with numerous nucleating grains appearing proximal to the SBs or deformed grain boundaries (GBs). Time dependent microstructure evolution was observed via ex-situ EBSD technique in the compressed specimens. Formation of new grains, increase in high angle grain boundaries (HAGBs), and dislocation annihilations were observed with the progress of time. The crystallographic texture evolution in the initial specimen was predominantly influenced by the S component. At lower strains, the fractions of Copper component increased, whereas at higher strains, a greater fraction of Brass and S components were induced. Following a 40% RR, a saturation in hardness value was observed, which could be potentially attributable to an accelerated rate of RT recrystallization in the case of 75% RR.

本研究针对经热处理后开展室温轧制（room temperature rolling, RTR）的Cu-0.13Sn-0.04Mg合金，探究其微观组织演化规律。将初始热处理后的试样在室温下分别以40%和75%的压下率（reduction ratios, RR）进行轧制，以开展微观组织与晶体织构分析。采用电子背散射衍射（electron backscattered diffraction, EBSD）与透射电子显微镜（transmission electron microscopy, TEM）对初始态与变形态微观组织进行表征。两类试样均呈现非均匀微观组织分布。初始试样中存在剪切带（shear bands, SBs），该剪切带在后续热处理过程中成为新晶粒形核的主要位点；室温轧制试样中的剪切带分布更为密集。值得注意的是，此类试样中观察到反常的自退火现象，最终在室温下形成再结晶晶粒。在严重变形的试样中存在大量此类晶粒，众多形核晶粒均紧邻剪切带或变形晶界（grain boundaries, GBs）分布。通过非原位电子背散射衍射（ex-situ EBSD）技术对压缩试样进行表征，观察到随时间演变的微观组织演化过程：随着时间推移，新晶粒持续形成、大角度晶界（high angle grain boundaries, HAGBs）占比升高，同时位错发生湮灭。初始试样的晶体织构演化主要受S分量调控。低应变条件下，铜组分占比升高；而高应变条件下，黄铜组分与S组分的占比显著提升。当压下率为40%时，试样硬度达到饱和；而压下率为75%时的硬度饱和现象，可归因于室温再结晶速率的加快。