Study On Fusion Weldability To Dissimilar Alloys Of Magnesium Alloy And Aluminum Alloy

With the increasing attention to energy saving and environment protection in the world wide, and the operation of the less-carbon-economy-model in China, the application fields of magnesium and aluminum alloys include not only aeronautic industry but transport industry such as ship, car, auto and railway. With the wider use of magnesium and magnesium alloys, the problem of joining magnesium to aluminum was unavoidable to meet. The joining of dissimilar metal magnesium and aluminum can bring their own good characters into play together, which was really expected. The technique development of joining magnesium to the other metals restricts the range of magnesium use and accelerates the use of magnesium. The progress in joining dissimilar will make more design program feasible and give the designer more choices. What's more, the study on joining dissimilar metal magnesium and aluminum alloys will make the flow in welding pool and element diffusion more obvious. As the most often used welding method, fusion welding of magnesium and aluminum alloys successfully was meaningful definitely.In this article, fusion welding method was adopted to join dissimilar metal magnesium and aluminum alloys. All kinds of joining form was attempted, including materials, welding wire, welding methods, current polarity and joining forms. The reason to the poor weld ability of dissimilar magnesium and aluminum alloys by arc includes the intermetallic compound formation between magnesium and aluminum, the poor wet ability of magnesium and aluminum under arc and the high volumetric thermal expansion coefficient of magnesium and aluminum alloys.The joining of magnesium and aluminum was made successful by fusion-brazing welding method with interlay plating. It was found that tin can be plated on the magnesium plate as an interlay through scratching the plate and dipping into tin. Definitely, Tin interlay increased the wetability of magnesium and aluminum under the arc, reduced the mount of intermetallic compounds produced, but not prevented the formation of intermetallic compounds completely. Therefore, the joint strength can only satisfy certain request.At this foundation, laser-arc hybrid welding method was adopted to realize the joint with higher strength. The hybrid welding technique to join magnesium and aluminum was studied. The relationships between the microstructure, micro hardness and strength separately were analyzed. The reason for the strength improvement by the laser-arc hybrid welding method was explainedBased on the cylinder coordinate, the thermo and fluid dynamic mathematics and physics model to the welding pool was built. The simulation adopted both laminar and turbulent model. The temperature, velocity and pressure field according to these two models were compared which made us understand the thermo and fluid dynamic behavior better. The simulation result shows the contact interface of lap joint magnesium and aluminum alloys was turbulent. And this simulation result was tested by the experiment result of spot joining magnesium and aluminum by arc.According to the above study of wedability, intermetallic and contact interface between these two dissimilar alloys, combining the metallurgical effect of various elements to magnesium alloys, the laser-arc hybrid seam welding method with cerium as interlay was developed. The microstructure, strength and fracture of magnesium and aluminum lap joint welding directly and with cerium as interlay were compared. The strength with different cerium thickness was examined. The influence of cerium to the welding pool flow and the strengthen reason by cerium were analyzed.