| In order to exert the performance advantages of magnesiμm- copper dissimilar metals, further expand the application of magnesiμm alloy in the field of high and new technology, it is necessary to connect magnesiμm with copper.Due to the difference of crystal structure and physical properties between Mg and Cu, it is difficult to obtain the Solid welding joint by the traditional welding technology.Diffusion brazing has the advantages of low welding temperature, uniform heating, small welding stress and deformation,it has received more attention in the welding of dissimilar materials. An appropriate intermediary material has a positive effect to promote the formation of welding joints, control the eutectic liquid layer thickness of interface area, inhibiting the formation of brittle intermetallic, It is an important approach to improve the properties of diffusion brazing welding joint.Respectively in this paper with Al foil, Ni foil and Al-Si-Cu alloy powder as an intermediate transition layer material to bond AZ31 B magnesiμm alloy and T2 copper by diffusion brazing method. Study the type of intermediary material, welding temperature and holding time on the influence law of microstructure and mechanical properties of the welding joint.Reveal the inner link between welding process and the performance of the joint, and propose the formation mechanism of joint, To provide the important test and theoretical basis for the development of AZ31B/Cu dissimilar metal welding research.Studies have shown that with Al foil as interlayer, the Cu/Al/AZ31 B diffusion braze welding joint can be obtained through the AZ31 B substrate and Al foil diffusion to form eutectic liquid to wetting and spreading Cu substrate under the conditions of 460℃~ 500℃、 10min~60min. When soldering temperature reaches 490 ℃, holding time is 20 min, the pressure is 2.5MPa, the microstructure of the joint are γ-Cu solid solution+Al Cu4/(Al3Mg2+Al5CuMg4+Mg2Cu) intermetallic compounds+(Mg17Al12 +α-Mg)eutectic structure/α-Mg solid solution. With the increase of welding temperature and holding time,the change of thickness of Cu side layer interface is not obvious, the middle eutectic layer and the Mg side transition layer are increasing, The overall thickness of the interface increased gradually;The microhardness of the joint interface zone was significantly higher than the two sides of substrate, the Cu side zone has reached the highest hardness of 265 HV.The shear strength of the joints increased at first and then decreased with the increase of the holding time, and the shear strength of the joint was the highest at 490℃ for 68 MPa. The shear failure of the joint occurred in the diffusion region near the Cu side.The diffusion brazing of AZ31B/Cu used Ni foil as interlayer, When soldering temperature is 490 ℃ < T < 510 ℃, holding time 10 min < T < 40 min, the Metallurgical properties of the joints are excellent. When soldering temperature reaches 500 ℃, holding time is 30 min,the microstructure of the joint are as follows:γ- Cu+ Al-Cu binary compounds / Cu11Mg10Ni9 +(α-Mg+Mg2Cu+NiMg2) eutectic structure/α-Mg solid solution. The thickness of the Cu side and the middle diffusion layer is increased, the Mg side diffusion layer gradually disappears, and The overall thickness gradually broadens with the increase of holding time and temperature;The microhardness of the joint was distributed with the different of the microstructure, and The highest hardness reached 284 HV. in the Cu side transition layer. The shear strength of the joints increased at first and then decreased with the increase of the holding time, and the shear strength of the joint was the highest at 500℃ for 71 MPa. The shear failure of the joint occurred in the diffusion region near the Mg side, The welding joint is ductile and brittle mixed fracture.The diffusion brazing of AZ31B/Cu use Al-Si-Cu solder as interlayer, When soldering temperature is 500 ℃ < T < 540 ℃, holding time 10 min < T < 40 min, the metallurgical properties of the joints are excellent,The thickness of the diffusion zone is wider with the increase of temperature and holding time. When soldering temperature is 540 ℃, holding time is 10 min,The Brazing seam zone from Cu to AZ31 B generate: γ-(Cu) + Al-Cu binary compounds /(α-(Mg) + Mg17Al12+Mg2Si) eutectic structure +Al-Cu-Mg ternary and Al3Mg2 binary compounds /α-Mg solid solution; The highest microhardness of the joint is the Mg lateral diffusion layer, then the eutectic layer, and the lowest is copper side diffusion layer. the highest hardness occurred 261 HV at Mg side.The shear strength of the joints increased at first and then decreased with the increase of the welding temperature, and the shear strength of the joint was the highest at 510℃ for 51 MPa. The shear failure of the joint occurred in the diffusion region near the Mg side,The welding joint is ductile and brittle mixed fracture. |
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