Study On Microstructure And Properties Of Magnesium Alloy Reinforced With LPSO Structure Preparated By Process Of Casting-extrusion Integration

Magnesium alloy is known as"green engineering material for the 21st century".Magnesium alloy has lower density(density is only 1.74g/cm³),higher specific strength and specific stiffness,better shock absorption performance and electromagnetic shielding ability The advantages such as are widely used in the automotive industry,aerospace and electronic products,but the absolute strength of magnesium alloys is low,and the plastic processing is difficult.The current magnesium alloys still have certain limitations in application,and they are grown in magnesium alloys.Long-period stacking ordered phase(LPSO)is a good response method,but the LPSO phase inside the casting obtained by conventional gravity casting is generally distributed in a coarse network at the grain boundary.This morphological structure is greatly It limits the strengthening effect of LPSO on the mechanical properties of magnesium alloys.Therefore,adopting effective material processing technology to refine the LPSO structure is essential to improve the performance of magnesium alloys.This article combines ultrasonic and squeeze casting with hot extrusion,and proposes a new process of casting and extrusion integration,using ultrasonic and pressure in the casting process to refine the solidified structure of the magnesium alloy,and then the alloy is hot extruded to further refine LPSO structure and matrix structure to improve the mechanical properties of the alloy.An integrated casting and extrusion die is designed to realize four new types of integrated casting and extrusion processes.These four processes are gravity casting+hot extrusion process,ultrasonic treatment gravity casting+hot extrusion process,extrusion casting+Hot extrusion process,ultrasonic treatment extrusion casting+hot extrusion process.First,the effect of ultrasonic treatment on the microstructure and mechanical properties of Mg_98.4Zn_0.5Y₁Zr_0.1 alloy prepared by casting and extrusion integration was studied.The Mg_98.4Zn_0.5Y₁Zr_0.1 alloy obtained without ultrasonic treatment contains a large amount of coarse and bulky LPSO phases.The LPSO phase is unevenly distributed.After ultrasonic treatment,the solute atoms are evenly distributed.The LPSO phase is significantly refined,and the ultrasonic enhancement of?-The nucleation ability of Mg grains refines the grain size.After ultrasonic treatment,the tensile strength,yield strength and elongation at room temperature are 281.6MPa,212.3MPa and 21.2%,which are higher than the hot-extruded magnesium alloy without ultrasonic treatment.Then the effects of squeeze casting on the microstructure and mechanical properties of Mg_98.4Zn_0.5Y₁Zr_0.1 alloy prepared by casting and extrusion were studied.The grain size of the Mg_98.4Zn_0.5Y₁Zr_0.1 alloy obtained without squeeze casting is relatively coarse.After squeeze casting,there are two grains with a large difference in size within the alloy,and the size of the two grains is relatively unsqueezed.The grains obtained by die casting are significantly smaller.After squeeze casting,the alloy showed excellent mechanical properties,its room temperature tensile strength,yield strength and elongation were325MPa,268.3MPa,22.4%.Combining ultrasonic treatment,squeeze casting and hot extrusion,the effects of extrusion ratio on the microstructure and mechanical properties of Mg_98.4Zn_0.5Y₁Zr_0.1 alloy prepared by a new casting-extrusion integration process were studied.The microstructure of the longitudinal section changes significantly,the shape of the?-Mg grains becomes elongated and distributed along the extrusion direction,and the corresponding LPSO phase distribution along the?-Mg grain boundaries also has directionality,along the extrusion The compression direction is distributed in strips,and after extrusion deformation,dynamic recrystallization phenomenon occurs in different degrees inside the alloy.As the extrusion ratio increases,the mechanical properties of the alloy tend to increase first and then decrease.When the extrusion ratio is 6:1,the mechanical properties of the alloy reach the maximum.