Study On Microstructure And Mechanical Properties Of AZ31/AZ80 Magnesium Alloy Sheets Prepared By Accumulative Extrusion Bonding

Magnesium alloys are widely used in automobile,electronics,aerospace and other fields due to their low density,high specific strength and stiffness.However,due to the low strength of some magnesium alloys,the further application of magnesium alloys in engineering field is limited.Accumulative extrusion bonding,as a new processing and forming method,can achieve large deformation through single pass extrusion.Based on this,AZ31 sheet,AZ80 sheet and AZ31/AZ80 magnesium alloy composite sheet were prepared by AEB process.The effects of extrusion passes and extrusion temperatures on the microstructure and mechanical properties of the AEBed sheet were systematically analyzed by metallographic microscope,scanning electron microscope and tensile test.The main conclusions are as follows:(1)For the AEBed AZ31 sheet: the dynamic recrystallization of grains occured after one pass of AEB at 250 °C,and the grains were refined obviously;after two passes,the grain size was not refined further;when the extrusion temperature rose 300 °C,the grains were slightly coarsened.The tensile strength of the sheet decreased slightly with the increase of the number of passes,while the elongation increased slightly.The yield strength,tensile strength and elongation of sheet processed by one-pass AEB at 250 °C increased by 3.4%,13.2% and 10.3% respectively compared with base metal.Its good mechanical properties were mainly attributed to grain refinement strengthening.When the temperature rose to 300 °C,the strength of one pass extruded sheet decreased,and the elongation reached the maximum of 19.4%.(2)For the AEBed AZ80 sheet: the grain size was obviously refined after one pass AEB treatment at 250 °C,but the number of passes had little effect on the grain size.When the extrusion temperaturere rose to 300 °C,the grain growth was obvious.The tensile strength and elongation of the sheet increased with the increase of the number of passes,and the tensile strength and elongation of one-pass and two-pass sheets processed at 250 °C increased by 9.5% and 16.7%,and 15% and 29% respectively compared with as-received sample.The yield strength and elongation of the sheet decreased slightly when the extrusion temperature increased to 300 °C.After aging treatment of AZ80 AEBed plate at two temperatures,it was found that the grain size of AZ80 composite plate changed little before and after aging,and a certain number of second phases appeared at grain boundaries and within grains.However,after aging treatment,the mechanical properties of the four kinds of sheets were equivalent;compared with aging base metal,all sheets showed better elongation,but its yield strength and tensile strength were lower than aging base metal.(3)For the AEBed AZ31/AZ80 composite sheets: the interface between AZ31 and AZ80 was well bonded,there was no interface separation,and the interface was straight.The number of extrusion passes had little effect on the grain size and mechanical properties of the composite plate.On the contrary,the mechanical properties of the composite plate decreased slightly with the increase of temperature.Among them,the mechanical properties of the sheet after one pass extrusion at 250 °C were the best.The yield strength,tensile strength and elongation of the sheet were 184 MPa,398 MPa and 20.5% respectively,which was superior to those of the base metal.After aging treatment,the yield strength of the composite sheet increased,while the tensile strength and elongation decreased.