镁/铝异种金属超声波焊接接头性能与界面反应

Joint performance and interface reactions in magnesium to aluminum dissimilar metals by ultrasonic welding

镁/铝异种金属焊接时焊缝极易形成脆性相,导致焊接结构性能低。为此采用超声波焊接技术减小反应层厚度,通过组织分析与纳米压痕测试,分析焊接能量对接头性能与界面反应的影响规律。结果表明:焊接能量为1 540 J时,焊缝界面出现熔化迹象,说明金属的高应变率塑性变形在热空位中引入了大量的过剩空位,使固态金属在平衡熔点以下液化。随线能量升高,γ-Mg17Al12+β-Mg2Al3相急速长大至厚度约为17μm,其中β相硬度高达663.26HV,γ相平均硬度为346.936HV。β相迅速长大使接头性能急剧下降。接头在界面处失效,断口形貌呈解理断裂并伴有大量二次裂纹。

The brittle phases are prone to form in the weld metal of dissimilar welding joint of Mg and Al and hence deteriorate the performance of welded structure. For this reason,the ultrasonic welding technology was used to reduce the thickness of reaction layer. The influence of ultrasonic welding energy on joint performance and interface reaction were investigated through microstructure analysis and nanoindentation technology. The results show that at the welding energy of 1 540 J there is evidence of melting in the weld joint,indicating that the high strain rate plastic deformation of the metal introduces a large number of excess vacancies in the hot vacancies,causing the solid metal to melt below the equilibrium melting point. As the line energy increases,the γ-MgAl+ β-MgAlphases rapidly grows to ones with a thickness of about 17 μm,wherein the β phase hardness value is up to 663.26HV and the average hardness value of γ phase is 346.936HV. The β phase rapidly grows and the performance of joint decreases rapidly. The failure occurs at the interface of joint. The fracture morphology is cleavage fracture and accompanied by a large number of secondary cracks.