Research On The Joint Interface Structure Of AZ31B Magnesium Alloy/6063 Aluminum Alloy By Ultrasound-assisted Soldering

Aluminum alloys and magnesium alloys are widely used in aerospace and aviation industries,because of their small density and high spe cific strength.But these two kinds of metal welding easily generate brittle intermetallic compounds,which is difficult to obtain the excellent joint.In the soldering process,how to choose the solder to avoid generating harmful intermetallic compounds,is the key to obtain high quality magnesium/aluminum dissimilar metal joints.In this paper,the self-made Sn-Zn-Ag,Zn-Sn-Cu and Mg-Al-Zn solders were used to weld the 6063 aluminum alloy/AZ31 B magnesium alloy by ultrasonic assisted soldering technology in atmosphere.By OM,SEM and EDS spectra observed and analyzed the microstructure and element distribution of brazed joints,by XRD analyzed the phase on both sides of the interface,the mechanical properties of welded joint were measured by using the universal mechanical testing machine,the experimental results are as follows :The experimental results show that using Sn-2.5Zn-2Ag solder under ultrasonic soldering magnesium/aluminum dissimilar metal can effectively prevent the formation of the Mg-Al brittle intermetallic compounds.However,there exist a large number of Mg-Sn intermetallic compounds at the interface between the weld and magnesium alloy,which is not conducive to the mechanical properties of the joints.Using the solder obtain the Mg/Al brazed joint,of which the average shear strength is 37 MPa,the fracture location of joints in the Mg-Sn intermetallic compound,which locate in the interface of magnesium alloy and soldering seam.At the same time,under the action of ultrasonic,Sn-Zn-Ag solder has dissolved the aluminum alloy matrix,and with the increase of ultrasonic time,the content of soldering seam dissolved in Al element also increase.When the ultrasonic time is 4.5s,Al element of dissolution distribute evenly in the whole soldering seam.Using Zn-Sn-Cu solder under ultrasonic soldering magnesium/aluminum dissimilar metal,the aluminum alloy side interface structure is mainly composed of the black Al Mg3 and Mg2 Sn,lamellar α-Mg + γ-Mg Zn pearlite;Magnesium alloy side interface structure is mainly composed of the black Mg-Al-Zn solid solution spots and the white reticular γ-Mg Zn microstructure.Zn base soldering filler metal is used for soldering magnesium and aluminum alloy,and a large number of Mg-Al intermetallic compounds are produced in the welded joints,which deteriorate the mechanical properties of the joint.The average shear strength of the joint is 18 MPa,the fracture mode is brittle fracture,and the fracture loca tion in α-Mg+γ-Mg Zn pearlite structure of the magnesium alloy side.Using Mg-Al-Zn solder soldering magnesium/aluminum dissimilar metal under ultrasonic,the interface microstructure of aluminum alloy side is mainly composed of primary α-Mg(Al,Zn),α-Mg(Al,Zn)+γ-Mg Zn pearlite structure;The interface microstructure of magnesium alloy side is mainly composed of eutectic γ-Mg17Al12 and α-Mg phase interphase arrangement.With the increase of ultrasonic time,the black boned α-Mg(Al,Zn)solid solution in the interface was gradually broken down and the morphology of black boned α-Mg(Al,Zn)solid solution in the brazing seam became more tiny,dispersing in the soldering seam.The average shear strength of the joint is 23 MPa,the fracture mode is brittle fracture,and the fracture location in the eutectic α-Mg + γ-Mg17Al12 structure of magnesium alloy side.