Recrystallization Behavior And Mechanical Properties Of Cast-roilling AT31and AT33Alloys

Generally, wrought magnesium alloys present excellent plastic processing capacity andmechanical properties. After processing, annealing treatment is needed to improve its stressand toughness. Most magnesium alloys have a lower recrystallization temperature. Withincreasing recrystallization temperature, second recrystallization will be occurred, which isharmful to mechanical performance. Recent researches have found that the second phasescan raise the recrystallization temperature and increase the resistance for grain boundarymigration. Therefore, grain growth can be restrained and mechanical properties will beimproved. Note that Mg2Sn with high hardness, high melting point, and coherent relationwith matrix, can be formed by the combination of Mg and Sn element. However, literaturesabout effect of Sn element on the microstructure and mechanical properties afterrecrystallization are very limited. Earlier it considered that Sn element is harmful to themechanical properties, which restricted researches onto magnesium alloys with Sn addition.In present study, attention will be focused on cast-rolling AT31and AT33alloys, toexplore effect of Sn element on microstructure and mechanical properties afterrecrystallization. Based on the recrystallization kinetics, recrystallization mechanisms aregiven as follws：(1) Microstructure of cast-rolling AT31and AT33alloys after recrystallization:With Sn addition, average grain siz of cast-rolling AT33alloy magn can berefined and grain structure become more uniform after annealing. At lower annealingtemperature, the second phases precipitated at grain boundaries, while they grown upat higher temperature. With temperature lower than270℃forcast-rolling AT31and 310℃forcast-rolling AT33alloy, grain growth will be impossible during annealing.At the same time, strong basal texture in cast-rolling alloys will be generated withincreasing Sn contents, and preferred nucleationin and grain growth will be suppressed.But a weaker texture observed in cast-rolling AT31alloy rather than cast-rolling AT31alloy when annealing temperature is higher than400℃.(2) Recrystallization kinetics of cast-rolling AT31and AT33alloys:The recrystallization rate will be restrained in lower temperature but promoted inhigher temperature with Sn addition. The grain growth (Qrex) and recrystallization (QG)activation energy for cast-rolling AT31and AT33alloys are84kJ/mol,137kJ/moland107kJ/mol,132kJ/mol, respectively (Qrex(AT33)> QG(AT33)> QG(AT31)>Qrex(AT31)). Equation of grain growth for cast-rolling AT31and AT33alloys are givenas, AT31:D2D203.55texp(12867T)and AT33:D2D215900218.03texp(T).(3) Tensile properties of room temperature for cast-rolling AT31and AT33alloys afterrecrystallization:Higher strength and ductility can be seen for AT33alloy compare with AT31alloy.Within grain size of3m–100m, the distribution of grain size has a larger effect onductility than strength, e.g. higher ductility can be seen in alloy with morehomogeneous grain size. Note that it is not the distribution of grain size but theaverage grain size that determined the strength. With increasing annealing temperature,Sn element will dissolve, leading to the increase of0and decrease of k in H–Pequation. Note that k value in cast-rolling AT33alloy is lower than that in AT31alloy,while0value is higher than AT31alloy. Tensile strength of cast-rolling AT33alloypresents ageing characteristic with time. The best heat treatment generated at210℃within1h for cast-rolling AT31alloy, e.g. tensile strength is273MPa andelongation–to–failure is22.5%, while it generated at270℃within4h forcast-rollingAT33alloy alloy, e.g. tensile strength is291MPa and elongation–to–failure is24.6%.