| 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 AZ31 B 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:?-Mg?Mg-Cu-Al ternary intermetallic compounds?(?-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 10 min. The fracture surface of the joint is located at the interface near thetitanium 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:?-Mg solid solution, Mg-Al-Zn ternary intermetallic compounds and(?-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 AZ31 B 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 70-80 A. 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 80 A. |
PDF Full Text Request