Effects Of Aging And Extrusion On The Microstructure And Mechanical Properties Of Mg-Al-Sn-Zn Alloy

Light metal magnesium alloy has outstanding advantages and excellent wrought performance,with good prospect of development.The extruded magnesium alloy grains are refined.Aging treatment affects the precipitation behavior of the second phase,thus can improve mechanical properties of the magnesium alloy.In this paper,AZ61,ATZ641,and ATZ842 alloys were obtained by gravity casting.The microstructure and mechanical properties of AZ61 and ATZ641 alloys were studied according to the as-cast-solid solution-extrusion-aging processing sequence.Different extrusion conditions were used for lateral comparison to find the best wrought parameters.Microscopic morphology and mechanical properties of the extruded specimens were compared to explore the strengthening effects of aging on the materials.ATZ842 alloy were studied according to the as-cast-solid solution-aging-extrusion processing sequence.To study its effects,artificial aging was performed for 600 hours.After that,microscopic morphology of the extruded state was observed.Results showed that the as-cast ATZ alloy had coarse grains and segregation phase.Solution treatment effectively eliminated pseudo eutectic metal compounds.The AZ61 and ATZ641 alloys after solution treatment were extruded,and it was found that when the extrusion temperature increased,the recrystallized grain size got larger;when the extrusion ratio was increased,the recrystallized grain size was small,and the precipitated phase was coarse.The aging treatment of the extruded AZ61 and ATZ641 alloys greatly improved the strength of the alloy,by dispersion strengthening.When the extrusion temperature was 350°C and extrusion ratio was 32,yield strength of ATZ 641 reached 296 MPa,and the tensile strength reached 401MPa.The time of aging treatment changed regularly.With one extrusion temperature and different extrusion ratio,the peak aging time of each alloy remained unchanged.When the extrusion temperature was increased,the peak aging time of each alloy was shortened by 4hours.Under the same extrusion condition,the peak aging time of ATZ641 was longer than AZ61 with 4hours.The ATZ842 material was strengthened by pre-extrusion aging,so that the dispersion phase strengthening effect is remarkable.Under the extrusion temperature of 250°C and the extrusion ratio of 32,the yield strength reached 312 MPa,the tensile strength was 379 MPa,and the elongation at break was 7.5%.Some bright Mg2Sn precipitate was found in the as-cast microstructure,so was the gray Mg₁₇Al₁₂ precipitation.A poorly soluble Mg-Al-Zn ternary phase was found in the solid solution state.The material reached the peak of Wechsler hardness after 21 days aging.The grain boundary and a large number of precipitated phases in the crystal were observed in the microstructure,and the morphology of the precipitated phase was different.There are smaller precipitates in the twinned zone than in the crystal.Dynamic recrystallization occured in the extruded state,and the nanoscale precipitation phase improveed the properties of the material.