Study On Contact Reactive Brazing Of Mg/Al Dissimilar Metals With Zn Base Nano Carbon Composite Interlayer

As important lightweight structural materials,magnesium alloys and aluminum alloys have broad application prospects in the fields of aviation,aerospace and automobile manufacturing.The trend of cross application is more and more prominent.The high quality and high efficiency connection of Mg/Al dissimilar metal has become the focus and nodus in the welding field.A large number of brittle intermetallic compounds are easily formed in the Mg/Al joint obtained by the conventional welding method.The contact reactive brazing technique added with suitable transition metal not only can achieve the effective connection of Mg/Al dissimilar metals,and suppress the formation of brittle intermetallic compounds to a certain extent,but also can improve the microstructure and properties of the joints.Nano-carbon structural materials with super high strength and good deformation performance are ideal metal matrix composite reinforcements,which have made breakthrough progress in the field of welding applications.It is bound to increase the performance of the joints if the nano carbon materials are added into the Mg/Al joints and disperse effectively.In this paper,the contact reaction brazing of AZ31 magnesium alloy/6061 aluminum alloy dissimilar metals was carried out by adding composite powders containing GNPs,Zn-5Al-GNPs and Zn-5Al-GNSs in the middle layer.Through the comparison of different process conditions,the best preparation method of the intermediate layer was determined,and the influence of GNPs and GNSs on the microstructure and mechanical properties of the joints as well as its strengthening mechanism were analyzed.Using the method of shielding and inert gas directional blowing-mechanical stirring-hot dipping,the middle layer of Zn-5Al-GNPs and Zn-5Al-GNSs was prepared on aluminum substrate,GNPs and GNSs were both effective dispersion.The best hot dip process:the hot dip temperature was 410 ?±3 ?,the hot dip time was 30 s.The shear strength of Mg/Zn-5Al-GNPs/Al contact reactive brazing joints increased first and then decreased with the increase of GNPs contents.When the amount of GNPs was 1.0 wt%,the shear strength of the joints reaches the maximum value of 102 MPa,compared with Mg/Zn-5A1/Al contact reactive brazing joints increased by 34.2%.Similarly,the shear strength of Mg/Zn-5Al-GNSs/Al contact reactive brazing joints increased first and then decreased with the increase of GNSs contents.When the amount of GNSs addition was 0.24 wt%,the shear strength of the joints reached the maximum value of 87MPa,which increased by 14.5%compared with that of the Mg/Zn-5Al/Al contact reactive brazing joints.In joints of Mg/Zn-5Al-GNPs/Al and Mg/Zn-5Al-GNSs/Al,both GNPs and GNSs have good interfacial bonding with A1 based solid solution and have bridging effects with MgZn2 grains to realize direct reinforcement.