摘要
The influence of ultrasonic vibrations on microstructure and mechanical properties of the AZ91-C magnesium alloy after ultrasonic assisted friction stir welding(UaFSW)in comparison with conventional friction stir welding(FSW)was investigated.The FSW was applied at the rotational speed of 1400 r/min and welding speed of 40 mm/min and no defects were observed.Using the same welding parameters,the process was carried out with inducing ultrasonic vibrations to the weld line at the amplitude of 15μm.The microstructure of the specimens was observed with optical and scanning electron microscopy.The results indicate that a very fine microstructure is obtained in UaFSW with respect to that of conventional FSW.Moreover,β-Mg17Al12 coarse dendrites are segregated to very fine and partly spherical particles that homogeneously distribute inα-Mg matrix.This remarkably-modified morphology of microstructure attributed to severe plastic deformation comes from ultrasonic vibration and friction stirring effect.Tensile and hardness tests were performed to evaluate the mechanical properties of the welds.According to the results,the vibration greatly improves the mechanical properties of the conventional FSW joint.The tensile strength and hardness are increased from 195 MPa and HV 79 in conventional FSW to 225 MPa and HV 87 in UaFSW,respectively.
将超声辅助搅拌摩擦焊(UaFSW)与传统搅拌摩擦焊(FSW)相比,研究超声振动对AZ91-C镁合金显微组织和力学性能的影响。当FSW的转速为1400 r/min、焊接速度为40 mm/min时,没有观察到缺陷。在相同条件下,引入振幅为15μm超声振动,用光学显微镜和扫描电镜观察样品的显微组织。结果显示,与传统FSW相比,Ua FSW焊缝的显微组织更细小,原先粗大的β-Mg17Al12枝晶被分离成非常细小、部分球形的颗粒,且均匀分布在α-Mg基体中。在超声振动和搅拌摩擦的共同作用下,材料产生严重的塑性变形,使显微组织发生明显的变化。焊缝拉伸和硬度测试的结果显示,超声振动大大提高传统FSW接头的力学性能,UaFSW焊缝的抗拉强度和硬度分别从195 MPa和HV 79提高到225 MPa和HV 87。
