Study On Microstructure And Properties Of Rare Earth Magnesium Alloy Ultrasonic Welded Joint

As environmental problems become increasingly serious,lightweight materials are receiving more and more attention from the market.Magnesium alloys,as the lightest metal structural materials,have gradually become a research hotspot.The rare earth magnesium alloy prepared by using the high-abundance rare earth element Ce has significant advantages such as low cost and high performance,and is an ideal lightweight material for engineering applications.It should be pointed out that the integration and manufacture of lightweight equipment inevitably requires welding.However,the conventional precipitated phases in magnesium alloys are easily softened by the influence of welding thermal cycles.Obviously,solid-phase welding methods such as ultrasonic welding and The combined use of thermally stable precipitates has unique advantages for the welding of light metals with poor weldability.Therefore,it is particularly necessary to study the ultrasonic welding of magnesium alloys with 0.4wt.%Ce added.In this paper,the response surface method is used to optimize the parameters of ultrasonic welding of rare earth magnesium alloys;taking the maximum tensile shear force of the joint as a reference value,the optimal process parameters are obtained:the welding energy is set to 2500 J,the welding pressure is set to 0.5 MPa,and the welding amplitude is set to 100μm.The microhardness and tensile properties of the welded joint obtained under the optimal process parameters are better than those of the base metal.By changing the welding energy to observe the influence of this key parameter on the welded joint,it is found that the tensile shear force increases first and then decreases with the increase of welding energy,and the excessively high welding energy leads to the decline of the mechanical properties of the joint.Microstructure and composition analysis found that the base metal structure is mainly composed of equiaxed grains with a grain size of 300-400μm,the precipitated phases in the base metal are mainly Mg₁₇Al₁₂ and Mg Zn₂ eutectic phases at the grain boundaries,and the grains are particles like Al₁₀Ce₂Mn₇ phase and long needle-like Al₁₁Ce₃ phase.At the same time,the strengthening mechanism of welded joints under the dual effects of high-frequency ultrasound and rare earth elements was analyzed.High-frequency ultrasound promoted the recrystallization of grains,and the grains were refined.At the same time,the large-sized Mg₁₇Al₁₂ phase at the interface was broken into small particles;and the rare earth element Ce has low solid solubility in magnesium alloys,and it is easy to precipitate rare earth phases at the grain boundaries,which can effectively hinder the grain boundary slip during deformation and improve the mechanical properties of magnesium alloy welded joints.