| In recent years,with the increasing demand for lightweight alloys,magnesium and aluminum alloys have developed rapidly,the addition of Li element with a density of 0.534 g/cm3 can not only improve the machinability of the alloy,but also further reduce the density of the alloy,Due to the particularity of magnesium/aluminum alloys,the connection of the two alloys will enable these alloys to be applied in more fields,thereby achieving ideal weight savings.Copper and its alloys have been widely used in many fields due to their excellent properties.Based on the application of electronic components with extended Cu substrate,the reliable connection between magnesium alloy and copper is realized by welding,and the performance advantages of each material are fully utilized.In this paper,the friction stir welding technology of LAZ931 magnesium-lithium alloy/LAZ931 magnesium-lithium alloy and AZ31 magnesium alloy/1420 aluminum-lithium alloy was analyzed.Under normal atmospheric environment,the Mg/Al/Cu dissimilar alloys were connected by ultrasonic induced transient liquid phase welding.In the friction stir welding process of LAZ931 magnesium lithium alloy,the good welding of magnesium lithium alloy was realized.For the thermomechanically affected zone in the joint,the grain structure in this zone is dominated by deformed grains,and the weld nugget zone in the joint is the main area of grain refinement.The grains not only undergo complete dynamic recrystallization,but also grow to a certain extent.The tensile test results show that the tensile strength of the joint is up to 176.8 MPa when the stirring head speed is 1400 rpm and the welding speed is 500 mm/min.The fracture of the j oint is full of dimples,so the fracture characteristic of the joint is ductile fracture.The good welding of Mg-Al-Li alloy was realized in the friction stir welding process of AZ31 magnesium alloy and 1420 Al-Li alloy.At the interface junction,bright white thin layers of different thicknesses are embedded in gray Mg and extend downwards in the direction of 45°.XRD analysis shows that there are Al3Mg2 and Al12Mg17 intermetallic compounds in the joint.The tensile test results show that the maximum tensile strength of the joint is 87.2 MPa when the rotation speed is 900 rpm and the welding speed is 100 mm/min.The fracture of the joint obtained is river-like,and the fracture form of the joint is cleavage fracture.Therefore,the fracture characteristic of the joint is brittle fracture.In the atmospheric environment,the Mg/Al/Cu dissimilar alloy was successfully connected by ultrasonic-induced transient liquid phase welding.The eutectic liquid phase was produced in the welded joint,and the phase composition was analyzed.The gray intermetallic compound dispersed in the eutectic structure was MgAlCu,and the black bubble substance was Mg17Al12.Tuah poku reaction model is established for analysis and calculation.It takes 5.6 h to complete the connection of the system by traditional TLP process.The comparison shows that the introduction of ultrasonic vibration can obviously promote the diffusion and shorten the welding time.At the same time,three different binary eutectic reactions can be calculated according to the model,448℃ L(?)ε(Al30Mg23)+β(Al3Mg2)at temperature Play a leading role.The shear experiment shows that with the increase of ultrasonic vibration time,the average shear strength of the joint increases first and then decreases.When the ultrasonic vibration time is 20 s,the average shear strength of the joint is 72.5 MPa. |
