搅拌摩擦叠层制造细晶材料组织特征及显微硬度

Microstructure Characteristics and Microhardness of Refined Material by Friction Stir Laminated Manufacturing

采用搅拌摩擦叠层制造技术制备块体细晶铝合金试样,并对试样成形特点、不同区域的显微组织及显微硬度等进行了研究。结果表明:试样结构致密,无气孔等缺陷存在;两板叠加加工后,返回侧hook沟向加工中心区伸入,而前进侧的则向上弯曲,经过二次搅拌后,hook沟伸入内部现象消失,开始向上弯曲,与前进侧类似。组织观察发现主要由细小等轴晶组成,但晶粒尺寸大小不一。其中最表面一层中心区的晶粒最细小,越底部位置加工区的晶粒尺寸越大。最上层轴肩区内的晶粒发生异常长大,过渡区中晶粒由于受到二次搅拌而细化,但其下方带状层中的细小晶粒发生粗化。显微硬度测试发现沿厚度方向上叠层试样硬度自下而上呈不断升高的趋势,这与试样晶粒尺寸分布情况相符。

Aluminum alloy specimens with refined grains were prepared by Friction Stir Laminated Manufacturing （FSLM）, and the formation characterization, microstructure and microhardness in the different position of the FSAM specimens were studied. The results show that the specimens have very compact structure and no-defect on the cross section. After FSLM processing, the hook groove on the RS goes into the centre zone, however, the hook groove on the AS bends upwards. Experiencing second stirring of the tool pin, the phenomenon of hook groove into the intemal disappeares and begins to bend upwards, it is similar with on the AS. The FSLM sample is characterized by fine equiaxed grains, but their sizes are different for different positions. The grains of stirred central zone on the surface layer for the FSAM specimen are smallest, with the increase of the distance from the surface, the size has an increased trend gradually. However, the grains in the shoulder zone of the surface layer grow up abnormally, and the grains in the transition zone are refined again due to the second stirring action of the pin. There forms a thin band layer under the transition zone, and their grains have been dynamically recrystallized to start coarsen. According to the testing results, the microhardness of the FSAM specimen along the thickness presents an increased tendency from the surface to the root, and which are consistent with the microstructures distribution.