Study On Microstructure Evolution And Mechanical Properties Of Hot-Rolled AZ31B Magnesium Alloy

The subject of this study is AZ31B magnesium alloy.The effects of two different homogenization processes at 400 ℃(4 h,12 h,24 h)and 420 ℃(4 h,12 h,24 h)on the organization and mechanical properties of magnesium alloys are investigated,respectively.The improvement of the formability and alloy properties of AZ31B magnesium alloy sheet by two different hot-rolling processes,direct hot-rolling in the as-cast state and hot-rolling after homogenization,is investigated.Both processes successfully produced magnesium alloy plates with equal deformation of 30%,50%,and 75%using the rolling temperature of 400 ℃ and the rolling rate of 3770 mm/min,respectively.The microstructures of the specimens after different homogenization and the rolling process are characterized by optical microscopy and SEM-EBSD;Testing the mechanical properties of different specimens using a universal tensile testing machine.The experiments combined with a variety of advanced microstructure and characterization tools to effectively obtain the tissue evolution pattern of magnesium alloy during the homogenization or the rolling process.Additionally,the crystal phase field method(PFC)is used to reveal the recrystallization phenomenon and grain refinement mechanism with increasing deformation during the hot-rolling process from the perspective of numerical simulation analysis.The results of this work not only elaborate underlying knowledge on the correlation relationship between the recrystallization mechanisms and the mechanical properties but provide an effective approach to optimize the microstructure-mechanical properties of alloys.The following conclusions are drawn from the research:(1)The optimal homogenization temperature and time would be 420℃-12h.The mechanical properties of the alloy are significantly improved after homogenization,with a tensile strength of 238 MPa and an elongation of 15.7%.(2)In the hot-rolling deformation with 30%,the twin-induced recrystallization mechanism mainly dominates the recrystallization process;In the hot-rolling deformation with 50%,the twin-induced recrystallization mechanism and the strain-induced grain boundary migration mechanism(SIBM)mainly dominate the recrystallization process;In the case of 75%hot-rolling deformation,the mechanisms of SIBM and sub-grain growth mainly dominate the recrystallization process of the rolling deformation.The recrystallization process dominated by different mechanisms contributes to the improvement of the mechanical properties of alloys.Eventually,the specimens with the rolling deformation of 75%could obtain a high tensile strength(298 MPa)and considerable ductility(18.9%).(3)In the homogenized hot-rolling deformation with 30%,discontinuous dynamic recrystallization consisting of twin-induced recrystallization and SIBM mainly dominates the recrystallization process of rolling deformation;In the homogenized hot-rolling deformation with 50%,the recrystallization process of rolling deformation is dominated by a combination of twin-induced recrystallization as the main discontinuous dynamic recrystallization and progressive lattice rotation as the main continuous dynamic recrystallization;In the case of homogenized hot-rolling deformation of 75%,a continuous dynamic recrystallization mechanism mainly dominates the recrystallization process of rolling deformation.Ultimately,the specimens with 75%homogenized hot-rolling deformation can obtain high tensile strength(327 MPa)and considerable ductility(22.2%).(4)The direct rolling process consists of discontinuous dynamic recrystallization as the main recrystallization mechanism in the low deformation stage,and the recrystallization mechanism in the high deformation stage is a mixture of continuous and discontinuous recrystallization.In contrast,homogenized hot-rolling achieves the conversion from discontinuous dynamic recrystallization to continuous dynamic recrystallization,and finally obtains better mechanical properties than direct hot-rolling.