| Magnesium alloys are one of the lightest structural engineering materials, which not only have many properties such as low density, high specific strength and specific stiffness, but also have excellent thermal conductivity, magnetic conductivity, damping shock absorption and electromagnetic shielding performance. As magnesium alloys are easy to machine shaping, recycle and degradation, they become important green structural materials. With the increasing expanding of the application of magnesium alloys, magnesium alloys joining has become a one of the hot spots in the research field of material. Soldering, with its low heating temperature, can avoid the evaporation and oxidation of Mg, and reduce the brittle phase, pores, cracks and other defects in soldering joint. Therefore, soldering has become the preferred method for magnesium alloys joining.To solve the difficulties of the magnesium alloy soldering technology, a new magnesium alloy solder with low-toxic or non-toxic, low melting temperature and cost, excellent mechanical properties was developed. The soldering process also has been investigated in this paper. The reliable soldered joint of magnesium alloy was obtained by using this new magnesium alloy solder. As the solidus temperature of magnesium alloys varies from430℃to646℃, in order to improve solder technology and simplify operation, the melting temperature of alloy solder should be lower than the solidus temperature of the base metal. Sn and Zn are nontoxic, and also have low melting point. Because of the mutual diffusion and solid solution between Mg and Zn, the new alloy or compound is produced. Therefore, to choose Sn-Zn alloy as base, both the wettability and mechanical properties of solder have been improved by adding an appropriate amount of Al and through alloying. After a series of soldering test, the solder alloy system of Sn-Zn-Al alloy is finally determined. Results show that solder composed of Sn+33%Zn+proper Al can be used for soldering deformation magnesium alloy. The physical and mechanical properties of this solder are solidus temperature of196.9℃, liquids temperature of200.8℃, and tensile strength of58.6MPa.Argon atmosphere furnace soldering was chosen as the soldering method in this paper. Foil solder was preset between the two tested plates. The influence of different soldering parameters on the strength of solder joint was investigated. Then, procedure parameters for protective atmosphere furnace soldering of magnesium alloy are determined. Results display that the optimum parameters are:soldering temperature of380℃, holding time of15min, and clearance of (solder thickness)0.1mm.The fracture morphology, phase structure and microstructure of the soldering seam and interface has been analyzed by X-ray diffraction, optical microscopy, scanning electronic microscopy respectively. Results indicate that the soldering seam are mainly composed of solid solution of Mg and Sn respectively, Mg-Zn eutectic, compounds of Mg, Al, Sn, Zn, intermetallic compounds, such as Al2Mg3, MgZn, Mg2Sn, Mg2Zn11, Mg2Zn3and AlMg4Zn11,etc. The contact reaction between solder and base metal has happened through diffusion in the process of soldering. The more solid solution in the soldering seam region, the stronger the soldering joint. Through mechanical properties test, shear strength of soldered joint at the optimal technological parameters is up to33.85MPa.In conclusion, by the argon gas protecting furnace soldering method and the developed solder, without flux, in a suitable brazing process conditions, the soldered joint with high bond strength and excellent performance can be obtained. |
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