基于激烈切向形变的镁合金孪生诱发再结晶及织构弱化机理研究

The twin and texture of Magnesium alloy sheet at any direction could be improved by Intense tangential deformation(ITD). Rolling Forging and Rolling Technology(RFRT) was used to produce Intense tangential deformation. It had many advantages than cross rolling and asynchronous rolling and reciprocating bending technology, such as increasing of recrystallization quantity and dispersing of grain orientation and weaking of the basal texture and reducing of anisotropy of Magnesium alloy sheet. The forming property and mechanical properties of Magnesium alloy sheet at room temperature will be improved remarkably. It will be studied that twin type and twin microstructure evolution law and basal slip law and slip condition of non basal plane during Intense tangential deformation. It will be researched that the influence law of conditions of twinning induced recrystallization and Grain misorientation in grain boundary on recrystallization. It will be studied that grain orientation evolution law in the boundary of tensile twin and compression twin. It will be studied that the influence law of parameters of Intense tangential deformation on grain orientation of Magnesium alloy. The law of texture evolution and mechanism of texture weaken during twinning induced recrystallization will be researched. It will be studied that the influence law of Intense Tangential Deformation on microstructure and forming property and mechanical property. The relationship model between Intense tangential deformation and microstructure and texture intensity and anisotropy value and forming property and mechanical property will be determined.

激烈切向形变(ITD)是指大的切向应变速率和大的切向形变量，可以有效改善镁合金板材横向、厚度方向、径向方向上的孪晶组织及织构。本项目采用滚压—轧制复合工艺(RFRT))使镁合金板材产生激烈切向形变，克服了交叉轧制、异步轧制、往复弯曲等形变方法的不足，明显提高拉伸孪晶与压缩孪晶交界处的再结晶量，使晶粒取向分散，有效弱化了基面织构及板材的各向异性，显著提高镁合金板材的室温成形性能及力学性能。研究AZ31镁合金材料激烈切向形变时的孪生方式、孪晶组织演变规律、基面滑移规律、非基面滑移启动条件。研究孪生诱发再结晶的条件及晶界处取向差对再结晶的影响规律，研究拉伸孪晶与压缩孪晶的交界处的再结晶晶粒取向演变规律。研究镁合金材料经过激烈切向形变后织构演变规律以及织构弱化机理、微观组织、室温成形性能和力学性能影响规律，建立激烈切向形变—组织性能—织构强度—成形性能—力学性能之间关系模型。

镁合金材料在室温条件下成形性能低是制约镁合金材料工程应用的重要因素。科学研究发现，激烈切向形变能够加剧镁合金材料动态再结晶发生，有利于细化晶粒和弱化基面织构。本项目首次提出了滚压—轧制复合变形方法制备高性能镁合金板材，产生激烈切向形变，加剧了镁合金板材动态再结晶发生、产生更多的滑移系、产生更多的孪晶组织、使晶粒取向分散、细化晶粒、弱化基面织构、弱化了板材的各向异性，显著提高镁合金板材的室温成形性能及力学性能。.揭示了镁合金材料复合变形后的孪晶组织及动态再结晶机制，在高温复合变形时，孪晶界具有比较高的能量，促进了动态再结晶晶粒在孪晶周围和内部的形核，实现了完全动态再结晶，促进了镁合金材料的晶粒细化，提高了材料成形性能。确定了基于复合变形的镁合金孪生诱发再结晶机制。.揭示了镁合金材料复合变形后的晶粒细化机理，即材料发生压缩变形→孪晶组织形成→发生动态再结晶→孪晶消失→晶粒细化的组织演变过程，形成分布均匀的细小的晶粒组织。揭示了镁合金材料复合变形后的织构弱化机理，即晶粒取向垂直→晶粒取向偏转→晶粒取向紊乱→织构弱化。揭示镁合金材料激烈切向形变时孪生演变方式、孪晶组织、基面滑移、非基面滑移启动条件、晶粒尺寸等影响规律；揭示镁合金材料孪生诱发再结晶的条件、再结晶的晶粒取向及织构演变规律，建立了形变工艺参数—晶粒尺寸—织构强度—力学性能之间关系模型。.复合形变后的AZ31镁合金板材的晶粒尺寸、织构强度、施密特因子、力学性能等参数得到明显改善。经过复合形变后，组织分布均匀，平均晶粒尺寸达到为7.84μm，屈服强度为212MPa，抗拉强度为298MPa，伸长率为17.2%。在{0001}晶面、{11-20}晶面和{10-10}晶面上的织构强度分别是6.89、3.14、2.65。施密特因子（Schmid）为0.51。复合形变后的镁合金性能与初始状态相比，晶粒尺寸细化了72%、屈服强度提高了25.4%、抗拉强度提高了20.1%、延伸率提高了34.3%，在{0001}晶面、{11-20}晶面和{10-10}晶面上的织构强度分别弱化了54%、32%、41%，施密特因子（Schmid）提高了64%。

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