Effect Of Mg₂Sn On Microstructure And Properties Of Mg-3Sn-0.5Mn Alloy Prepared By Accumulative Roll Bonding

Mg-3Sn-0.5Mn（TM30）alloy is subjected to aging at 180°C.The effect of aging time on precipitate phase and grain size is investigated.The aging process parameters are optimized.The solution and aging TM30 alloys were deformed at 300°C by a means of accumulative roll-bonding,respectively.The effect of Mg₂Sn on the mechanical properties of accumulative roll-bonding TM30 alloy is analyzed by observing the microstructure evolution and mechanical properties.In order to discuss the characteristics of Mg₂Sn phase precipitation and deformation mechanism,the solution TM30 alloys are rolled by large strain rolling（LSR）,normal rolling（NR）and accumulative roll-bonding（ARB）at 300°C.The effect of Mg₂Sn on the deformation mechanism is revealed.The microstructure observation and microhardness test of the TM30 alloy aging at 180°C are carried out.The TM30 alloy aging at 180°C for 12 h with the most finest Mg₂Sn phase is chosen to roll.The solution and aging TM30 alloys rolled by ARB at 300°C are studied.The average grain size of the alloys has not changed significantly after the first pass-while the original grain elongates along the rolling direction,and forms（002）basal plane texture.After the second pass,the average grain size decreases significantly and the grains are nonuniform while the dynamic recrystallization occurs along the grain boundary.After the third pass,the average grain size of the solution TM30 alloys is about 8.11μm,the average grain size of the aging TM30 alloys is about 6.97μm,and the structure is homogeneous.After the first pass,the Mg₂Sn phase precipitates at grain boundary.After the second pass,the precipitated phases appear at the deformation twins and dislocations.After the third pass,the precipitated phases arise in the matrix and are distributed more homogeneously.The fine Mg₂Sn phases refine the microstructure due to their pinning effect on the grain boundary and dislocation during the process of deformation.The tensile strength of the solution TM30 alloy with two passes roll-bonding reach to 259.40 MPa,which is 50% higher than the solution alloys（172.85MPa）.The elongation rate decreases after rolling.The elongation rate of the solution alloy is 11.31%,while the elongation of the alloy after three passes is reduced to 2.93%.The tensile strength of the aging TM30 alloys after the process of two passes roll-bonding reach to 267.8MPa,54.70% higher than the tensile strength of the aging alloy（173.11MPa）.The elongation decreases from 10.09% to 2.39%.The grain refinement of the solutuion TM30 alloy caused by dynamic recrystallization occurs during the process of LSR at 300℃.With the rolling pass increasing,the nucleation number of dynamic recrystallization and growth driving force increase.Coarse raw grain is gradually replaced by fine recrystallized grain.Finally the uniform grain structure is obtained.During the process of LSR,the precipitation of Mg₂Sn phase is mainly found at the twinning along the grain boundary.With an increase in the amount of total deformation,the number of grain boundary and twinning increase,the size of grain decrease and the precipitation of diffuse and fine Mg₂Sn phase increase.The Mg₂Sn phase further pinns up the dislocation and the grain boundary and causes the grain refinement.The average particle size of alloy treated by LSR with the 87.5% total deformation is 10.20μm.The deformation mechanism of solutuion TM30 alloy rolled by NR at 300 ℃is mainly twining deformation.During the process of NR,many twining are found.The total deformation is 87.5% and the average particle size of alloy is about 14.30μm.During the process of normal rolling,the Mg₂Sn phase precipites in large quantities.Finally,the Mg₂Sn phases gather into small bar pieces.The total deformation of the three processing technology is 87.5%.Compared to LSR and ARB,the Mg₂Sn phase size of NR is coarsest.The effect of coarse phase on grain refinement is not obvious.The TM30 alloys rolled by LSR,NR and ARB are discussed.The grains rolled by ARB are fine and uniform.The grain rotation and grain boundary movement are easy to occur.Therefore,under the same deformation,the TM30 alloy sheet rolled by ARB has the highest tensile strength and elongation.