Study On The Mg Alloy And Ti Alloy Joint By Transient Liquid Phase Bonding Process

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 save materials.In this paper, the purpose of research is to explore the welding properties of magnesiumtitanium dissimilar materials(AZ31B/Ti-6Al-4V) by transient liquid phase bonding(TLP). High purity Ni foil,Cu foil and Al foil were selected as intermediate layer. Microstructure, element behavior and mechanical properties with different intermediate layer materials and technology parameters were analyzed by means of optical microscope, scanning electron microscope(SEM) accompanied by EDS, microhardness and strength analyzer. The good welded joint status was obtained by the optimization of the technological parameter.The results show that: Good surface welding joint can be got under porper brazing parameter(bonding temperature is 520℃~540℃, holding time is 5min~30min) by Ni, Cu or Al foil as intermediate layer. The microstructure from magnesium side to titanium side at interface zone of AZ31B/Ni/Ti-6Al-4V diffusion brazing joint includes α-Mg solid solution,(α-Mg+Mg-Al-Ni) eutectic structure, Mg-Al-Ni ternary intermetallic compounds, Ti3 Al intermetallic compounds Ti(Mg,Al) solid solution, and small amount of Mg17Al12. The microhardness from Ti-6Al-4V side to AZ31 B side decreases continuously. When the welding temperature was 520℃ and the holding time was 10 min, the microhardness of the joint reached the maximum, about 330.09 HV.As the welding temperature increases, the shear strength shows an increasing trend at first and then decreases. When the welding process is 520℃ keeping for 10 min, the highest shearing strength of the joint can reach 61 Mpa, which reaches approximately 43% AZ31 B magnesium alloy. Welding joint cracks along Ti/Ni interface, and the surface is ductile-brittle hybrid fracture.Good surface welding joint can be got under porper brazing parameter by Cu foil as intermediate layer. The microstructure from Ti-6Al-4V side to AZ31 B side at interface zone of diffusion brazing joint includes γ-Cu solid solution, Cu3 Ti, Cu2 Al, Mg-Cu-Al ternary intermetallic compounds, Mg17(Cu,Al)12 and(α-Mg+Mg2Cu) eutectic structure. The microhardness from Ti-6Al-4V side to AZ31 B side first increases and then decreases. When the welding temperature was 520℃ and the holding time was 20 min, the microhardness of the joint reached the maximum, about 292.87 HV. As the welding temperature increases, the shear strength shows an decreasing trend at first, then increasing and finally tends to decrease. When the welding process is 520℃ keeping for 20 min, the highest shearing strength of the joint can reach 69 Mpa, which reaches approximately 49% AZ31 B magnesium alloy. Welding joint cracks along Cu/Mg interface, the surface is ductile-brittle hybrid fracture.The metallurgical connection of AZ31 B magnesium alloys and Ti-6Al-4V titanium alloys were achieved when using Al foil as intermediate layer. The microstructure from Ti-6Al-4V side to AZ31 B side at interface zone of diffusion brazing joint includes α-Ti solid solution, Ti3 Al chemical compounds,(α-Mg+Mg2Al) eutectic structure and small amount of Mg17Al12 chemical compounds. The microhardness decreases of ladder shape. When the welding temperature was 540℃ and the holding time was 10 min, the microhardness of the joint reached the maximum, about 306.87 HV. As the welding temperature increases, the shear strength shows an increasing trend at first and then decreases. When the welding process is 540℃ keeping for 20 min, the highest shearing strength of the joint can reach 71 Mpa. Welding joint cracks along Ti/Al interface, and the fracture surface of joint showing dimples.