Preparation Of Magnesium Alloy Profiles For High-speed Rail Bodies And Research On Friction Stir Welding Technology

Lightweight is a trend in the development of high-speed railway,and realizing light-weight is of great significance to the development of high-speed railway.Magnesium alloys have broad application prospects in rail transportation and other fields because of their advantages of low density and high specific strength,but their application scope is limited due to problems such as low absolute strength and low ignitability.Taking two magnesium alloys AZ31 and AZ91-0.8Y-0.4Ca as the research object,this paper mainly analyzes the hot extrusion process of the two extrusion profiles,explores the effect of solution aging treatment on the mechanical properties of magnesium alloy profiles,and looks for the best welding process of magnesium alloy friction stir welding.When the extrusion temperature is 400℃ and the extrusion ratio is 25.2,the AZ31 magnesium alloy profile has a fine structure,the average grain size is 6.00μm,the yield strength is 175.41 MPa,the tensile strength is 295.46 MPa,and the elongation is 18.48%.After aging treatment at 225℃×8h,the structure is more uniform,the mechanical properties of the profile are improved,the yield strength and tensile strength are 180.34 MPa and 320.16 MPa,and the elongation rate is 22.29%.The AZ31 magnesium alloy plate with a thickness of 3.5mm is welded by friction stir welding.When the rotation speed is 1000r/min and the welding speed is 150mm/min,a high-quality welded joint can be obtained,the tensile strength is 294.37 MPa,and the elongation is 10.84%,the joint strength reaches 99% of the base metal.The microhardness distribution of the joint shows a trend of W,with the highest hardness value in the weld nugget zone and the lowest hardness value in the heat affected zone,and the fracture mode of the joint is ductile fracture.Adding Y and Ca elements to AZ91 magnesium alloy is to improve the mechanical properties and thermal stability of the alloy.AZ91-0.8Y-0.4Ca magnesium alloy ingots are prepared by smelting.When the extrusion temperature is 320℃ and the extrusion ratio is 25.2,the structure of AZ91-0.8Y-0.4Ca magnesium alloy is fine and uniform,the average grain size is 8.70μm,the second phase is dispersed,the mechanical properties are better,and the yield strength is 177.35 MPa,the tensile strength is 300.02 MPa,and the elongation is 14.25%.After aging treatment at 165℃×10h,the microstructure was more uniform,the yield strength and tensile strength reached 200.56 MPa and 351.69 MPa,and the elongation reached 13.24%.AZ91-0.8Y-0.4Ca magnesium alloy plates with a thickness of 3.5mm were welded by friction stir welding.When the rotation speed is 1000r/min and the welding speed is100mm/min,the joint is well formed,the tensile strength is 290.48 MPa,and the elongation is9.42%.The strength of the joint reaches 96% of the base metal,and the fracture mode of the joint is brittle fracture.