镁合金具有密度小、比强度高、制造成本低、散热性好等优点而逐渐受到重视，但由于镁合金在高温条件下的力学、耐腐蚀性能等不理想而很大程度限制了其广泛应用。钛合金由于具有高的比强度、耐热与耐蚀性好、断裂韧性强等特点，而在航空航天、医疗器械、地质勘探等领域逐渐得到广泛应用。为了发挥镁钛异种金属各自的性能优势，进一步扩大镁合金作为结构件在高新技术领域的应用，很有必要将镁合金与钛合金连接起来获得界面结合牢固的焊接接头,这样既可以降低结构重量又可以发挥各自性能。 本文对镁合金AZ31B与钛合金TC4进行了夹层扩散钎焊和熔钎焊（TIG）实验，利用金相显微镜、扫描电子显微镜(SEM)、能谱分析(EDS)、显微硬度计、剪切强度分析等测试方法，测试、分析了焊接接头界面的微观结构、主元素的扩散行为以及力学性能，研究了焊接工艺对微观结构、主元素的扩散行为以及力学性能的影响规律。 研究得出如下结论：⑴Cu+Al双夹层AZ31B/TC4扩散钎焊接头扩散区的显微组织由α-Mg及沿其晶界分布的Mg17(Cu, Al)12、Mg-Cu-Al化合物以及（α-Mg+ Mg17(Cu, Al)12+ Mg2Cu）共晶体组成。 ⑵Cu+Al双夹层的AZ31B//TC4扩散钎焊接头扩散区的显微硬度值从钛合金一侧至镁合金一侧呈逐渐变小的变化趋势；接头的剪切强度随保温时间的延长呈先增加后减小的变化规律，520℃、10min时接头的剪切强度达到最大60.5 MPa，接头的断裂面位于界面靠近Ti基体一侧，断口由许多小平台构成。 ⑶在520℃-540℃、5min-30min条件下，ZnAl15夹层的AZ31B/TC4扩散钎焊接头扩散区的组织组成物包括α-Mg固溶体、Mg-Al-Zn化合物及（α-Mg+ Al6Mg11Zn11）共晶体。 ⑷ZnAl15夹层的AZ31B/TC4扩散钎焊接头扩散区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。接头剪切强度随着保温时间的延长呈先增加后减小的规律，520℃、20min时的剪切强度达到最大值71MPa，约为AZ31B母材的49.6%，断口由不同大小、形状不规则的冰晶状物相组成，呈现沿晶断裂特征。 ⑸焊接电流对AZ31B/TC4的TIG熔钎焊焊接头的界面结合影响较大。60A的AZ31B/TC4的TIG熔钎焊焊接头界面以机械结合为主；焊接电流为70-80A时，接头界面以冶金结合为主。随着电流的提高，接头扩散区宽度增大。在其他工艺条件相同时，镁板在上、钛板在下的搭接形式的接头结合状况优于钛板在上、镁板在下的搭接形式，且其接头的剪切强度随着焊接电流的增大而增加，焊接电流为80A、Al夹层的接头剪切强度最大，约为58MPa。

Magnesium alloys have the properties of high specific strength, high specific modulus, low density, low manufacturing costs, good heat dissipation, good damping shock resistance, good electromagnetic shielding and so on. More and more people pay attention to magnesium alloys. However, the bad mechanical properties at high temperature and low corrosion resistance limit the application of magnesium alloys. Because of its high specific strength, good heat resistance and corrosion resistance, high fracture toughness and so on, titanium alloys can be used in the field of aerospace and geological exploration. In order to make full use of dissimilar metals’ performance advantage, to expand the application of magnesium alloys as the structure parts in the field of high technology, it is necessary to connect the magnesium alloys and titanium alloys to get interfacial bonding firm weld joints, which can reduce the structure weight and each performance advantage is developed. In this paper, the diffusion brazing and weld brazing (TIG) experiments of magnesium alloy TC4 and titanium alloy AZ31B were carried out.The interface microstructure, main elements of the diffusion behavior and mechanical properties of weld joint were analyzed and tested by means of optical microscope, scanning electron microscope (SEM) accompanied by EDS, microhardness and strength analyzer.The effect of welding process on microstructure, diffusion behavior and mechanical properties of the main elements was studied. The results of the study are as follows: (1)Diffusion zone microstructure of the diffusion brazing joint with Cu+Al as interlayer include：α-Mg、Mg-Cu-Al ternary intermetallic compounds、(α-Mg+ Mg17(Cu, Al)12+ Mg2Cu) eutectic and Mg17(Cu, Al)12 compounds which were distributed along the grain boundaries. (2)Diffusion zone microhardness of the diffusion brazing joint with Cu+Al as interlayer decreased from the titanium side to the magnesium side; With the increase of holding time,the shear strength shows an increasing trend at first and then decreases. The shear strength reached the maximum, about 60.5 MPa, when the welding temperature was 520℃ and the holding time was 10min. The fracture surface of the joint is located at the interface near the titanium side, and the fracture surface is composed of many small platform. (3)Diffusion zone microstructure of the diffusion brazing joint with ZnAl15 as interlayer include:α-Mg solid solution, Mg-Al-Zn ternary intermetallic compounds and (α-Mg+ Al6Mg11Zn11)eutectic under the condition of welding temperature is 520℃~540℃and holding time is 5min~30min. (4) Diffusion zone microhardness of the AZ31B//TC4 diffusion brazing joint with ZnAl15 as interlayer shows a stepwise distribution, reaching the maximum of micro hardness close to the titanium side and the minimum of that close to the magnesium side. The shear strength shows an increasing trend at first and then decreases with the increase of holding time. The shear strength reached the maximum to 71 MPa, about 49.6% of AZ31B base material. The fracture surface shows the intergranular fracture characteristic, composed of the crystals with different sizes and irregular shapes. (5)The welding current has a great influence on the interfacial bonding of TIG weld brazing joint in AZ31B//TC4. The TIG weld brazing joint interface in AZ31B//TC4 was mainly by mechanical bonding when the welding current was 60A; and the interface of that was mainly by metallurgical bonding when the welding current was 70-80A. The width of joint diffusion zone expands with the increase of electric current. The joint bonding state of the lap joints with magnesium plate above and titanium plate below is superior to those with titanium plate above and magnesium plate below under the same conditions. And the joint shear strength increases with the increase of welding current. The shear strength of the joint with Ai as interlayer reached the maximum about 58 MPa when the welding current was 80A.