Study On Interlayer Of Magnesium/Steel Dissimilar Metal Contact Reactive Brazing

The welding structure of magnesium alloy and steel can reduce the weight of components,thus realizing the lightweight of the whole structure,which is of great significance for saving energy and reducing pollution emissions.The physical and chemical properties of Mg and Fe are quite different,and there is neither solid solution nor metallurgical reaction between them.Therefore,magnesium alloys and steels are usually joined by means of transition materials.The reaction of elements in transition materials with matrix may lead to brittle intermetallic compounds in the joints,which is harmful to the mechanical properties of the joints.Contact reactive brazing can connect dissimilar metals by using interlayer as transition material.The effect of brittle intermetallics on mechanical properties of joints can be minimized by selecting a reasonable interlayer for welding.On this basis,the reinforcement phase is added to the joint to further strengthen and toughen the joint.Graphene has the advantages of high strength,high modulus of elasticity and good ductility.It is expected that the mechanical properties of the joints can be further improved by using the composite interlayer with graphene reinforcement phase for welding.In this paper,the Zn-xAl(x=3,5,7wt.%)interlayers were prepared on steel surface by hot dipping process.On this basis,the Zn-xAl-GNPs(x=3,5,7wt.%)composite interlayers containing multilayer graphene(GNPs)were prepared by inert shielding gas directionally blowing-mechanical stirring-hot dipping process.Contact reactive brazing experiments of AZ31 magnesium alloy/DCO1 steel with the above six types of interlayers.Then the microstructures and morphologies of the interlayers and joints were analyzed.It is found that the overall morphology of the Zn-xAl-GNPs interlayers and its joints did not change significantly compared with that of the Zn-xAl interlayers.The GNPs are more easily distributed around the Al-based solid solution.The shear strength of these six joints was tested.The results show that the shear strength of AZ31/Zn-5Al-GNPs/DC01 joint is the highest,112 MPa.The uniformly distributed Al-based solid solution in AZ31/Zn-5Al-GNPs/DC01 joint plays a role in strengthening and toughening MgZn2 and the GNPs connected between adjacent Al-based solid solutions bridge the joint structure and further improve the mechanical properties of the joint.