保温时间对AZ31B/ZnAl15/TC4扩散钎焊接头组织及力学性能的影响

为实现AZ31B镁合金与TC4钛合金的可靠连接, 采用ZnAl15作为中间层, 在520 ℃、0.01 Pa真空下对AZ31B与TC4进行了扩散钎焊试验, 研究了保温时间对焊接接头微观结构、显微硬度和剪切强度的影响。结果表明, 以ZnAl15为夹层的AZ31B/TC4扩散钎焊界面显微组织包括α-Mg固溶体、Mg-Al-Zn化合物以及α-Mg+Al₆Mg₁₁Zn₁₁共晶体。ZnAl15夹层AZ31B/TC4界面的显微硬度呈台阶式分布, 靠近钛侧的显微硬度值最大, 靠近镁侧的显微硬度值最小; 接头剪切强度随保温时间延长呈先增加后减小的规律, 520 ℃下保温20 min时的剪切强度达到最大值71 MPa, 约为AZ31B母材(82.4 MPa)的86.2%。接头拉伸断口由许多大小不等、形状不规则的冰晶状物相组成, 呈沿晶断裂特征。

Effects of Heat Preservation Time on Microstructure and Mechanical Property of AZ31B/ZnAl15/TC4 Diffusion Brazing Joint

In order to connect AZ31B magnesium alloy and TC4 titanium alloy, diffusion brazing of AZ31B and TC4 was carried out by using ZnAl15 as transition metal at 520 ℃ under vacuum condition of 0.01 Pa. The effects of heat preservation time on microstructure, micro-hardness and shear strength of the welding joint were studied. The results show that microstructures of AZ31B/ZnAl15/TC4 diffusion brazing interface include α-Mg solid solution, Mg-Al-Zn compound and α-Mg+Al₆Mg₁₁Zn₁₁ eutectic. The micro-hardness of the AZ31B/ZnAl15/TC4 interface is distributed in the form of steps. The micro-hardness value is the highest near the titanium side, and the lowest near the magnesium side. With the heat preservation time prolonging, the shear strength of the joint increases initially and then decreases. The joint shear strength of 71 MPa, which is 86.2% of AZ31B strength (82.4 MPa), can be achieved after 20 min heat preservation at 520 ℃. The tensile fracture surface of the joint is composed of many ice crystal phases that have different sizes and irregular shape. The fracture morphology is characterized by intergranular fracture.