Mg-6Sn-3Al-1Zn Alloys Preparation And Heat Treatment Process Of Study

This paper aims to study the preparation process of as-cast Mg-6Sn-3Al-1Zn alloy and obtain a Mg-6Sn-3Al-1Zn alloy with uniform structure and excellent properties.Through orthogonal experiments,the best solid solution conditions of the alloy are explored.After the solid solution treatment under the best solid solution conditions,the alloy is extruded and deformed,and the grain size distribution and excellent properties of the alloy extruded under different preheating temperatures and heating times are explored.The extruded alloy with uniform grain size and excellent properties is obtained,and then the extruded alloy is annealed for different times to finally obtain a bimodal structure with uniform grain size distribution and excellent properties.In the experiment,Mg-6Sn-3Al-1Zn alloy was prepared in an open smelting furnace under the protection of CO₂+SF₆ atmosphere.The solid solution treatment experiment and annealing experiment were carried out in a heat treatment furnace.The extrusion experiment was carried out by a four-column hydraulic press.In the whole experiment,the mechanical properties and microstructure of the alloy were analyzed and characterized by universal tensile testing machine,metallographic microscope（OM）,X-ray diffraction（XRD）and scanning electron microscope（SEM）,respectively,and the formation process of bimodal structure was explored.The experimental results show that Mg-6Sn-3Al-1Zn alloy is prepared under the protection of CO₂+SF₆ atmosphere in an open smelting furnace.When the melting temperature is 760℃,the heating time is 15min,the casting temperature is 720℃,and the standing time is 30min,the alloy has good comprehensive properties.At this time,the tensile strength,yield strength and elongation of the alloy reach 219MPa,82MPa and 16%respectively,and the grain size of the alloy is 133.35um.There are three phases in the alloyα-Mg matrix and Mg₂Sn phase.Mg₂Sn phase is mainly distributed on the boundary in blocks.The effects of time and temperature on the structure and properties of Mg-6Sn-3Al-1Zn alloy were investigated by two-factor and four-level experiments.When the temperature is changed from 300℃to 450℃,the Mg₂Sn phase increases first,then decreases and then increases,the grain size increases,the strength of the alloy increases first and then decreases,and the elongation increases with the increase of temperature;when the temperature is unchanged and the time rises from 4 h to 16h,the Mg2Sn phase increases first and then decreases,and the mechanical properties of the alloy almost all show first increase and then decrease.Situation.It was found that the Mg₂Sn phase was dissolved into the matrix at 450℃for 8h,and the alloy became finer and had good comprehensive mechanical properties.The extrusion of Mg-6Sn-3Al-1Zn alloy adopts two factors and three levels of experiments to explore the effects of different extrusion ratios and heating temperatures on the microstructure and properties of the extruded alloy.The extrusion ratio is 13:1 and 20:1 at 300℃and 350℃.When the temperature is constant,the extrusion ratio becomes smaller,the grain size becomes smaller,the grain size uniformity is better,and the tensile strength,yield strength and elongation of the alloy increase.When the extrusion ratio is fixed,the temperature decreases,the crystal grains are elongated,part of the crystal grains are broken,the tensile strength and yield strength increase,and the elongation decreases.There are three phases in extruded alloy:α-Mg matrix and Mg₂Sn phase.Mg-6Sn-3Al-1Zn alloy undergoes annealing treatment after extrusion.The elongated grains are firstly crushed and then dynamically recrystallized to form small grain distribution.The grain size distribution of the alloy obtained under different extrusion conditions is different after annealing,and the grain size distribution obtained under different annealing conditions is also different.It is found that when the temperature is 300℃,the extrusion ratio is 20:1,and the annealing condition is350℃to 10 min,the grain size distribution is uniform and the comprehensive mechanical properties are the best.