Ku Ming-Hsiang, Hung Fei-Yi, Lui Truan-Sheng
Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan.
Materials (Basel). 2019 Jan 10;12(2):227. doi: 10.3390/ma12020227.
The grain size of high strength 7075 hot-rolled aluminum plates was refined by a friction stir process (FSP) to improve their mechanical properties. The results of the tensile ductility tests, which were conducted at various tool rotational speeds, in the friction stir zone indicate significant tensile ductility loss, which even resulted in a ductile-to-brittle transition (DBT). DBT depends on the tool rotational speed. Our 1450 rpm specimens showed large data fluctuation in the tensile ductility and the location of the fracture controlled the formation of friction stir induced bands (FSIB). The crack initiation site located at FSIB was due to the tool rotational speed (1670 rpm). A higher heat-input causes the formation of FSIB, which is accompanied with micro-voids. This contributes significantly to tensile cracking within the stir zone after the application of the aging treatment. This investigation aimed to determine the dominant factor causing tensile ductility loss at the stir zone, which is the major restriction preventing further applications.
采用搅拌摩擦工艺（FSP）细化高强度7075热轧铝板的晶粒尺寸，以改善其力学性能。在搅拌摩擦区，于不同刀具转速下进行的拉伸延性试验结果表明，拉伸延性显著损失，甚至导致韧性到脆性的转变（DBT）。DBT取决于刀具转速。我们的1450转/分钟的试样在拉伸延性方面显示出较大的数据波动，并且断裂位置控制了搅拌摩擦诱导带（FSIB）的形成。位于FSIB处的裂纹起始点是由于刀具转速（1670转/分钟）。较高的热输入会导致FSIB的形成，并伴有微孔隙。这对时效处理后搅拌区内的拉伸开裂有显著影响。本研究旨在确定导致搅拌区拉伸延性损失的主要因素，这是阻碍进一步应用的主要限制因素。
