GWZ721镁合金型材挤压过程组织演变机制

对固溶处理的GWZ721（Mg-7Gd-2Y-1Zn-0.4Zr）镁合金坯锭在400 ℃进行热挤压变形，获得T型材。采用光学显微镜（optical microscope，OM）、扫描电子显微镜（scanning electron microscope，SEM）和电子背散射衍射仪（electron back scatter diffraction，EBSD）等设备，研究了挤压变形过程中该挤压锭不同部位的金属流变组织特点。结果表明：坯锭在挤压加载时组织发生大量孪生变形，进入模具型腔时发生明显动态再结晶和挤出后发生显著静态再结晶；其平均晶粒尺寸逐渐得到细化，第二相被破碎细化并弥散分布于基体中；形成了基面平行于挤压方向的织构，其最大相对强度先由弱变强然后再变弱；试制得到T型材的横截面显微组织均匀，晶粒尺寸细小，存在较弱的基面织构。

Microstructure evolution mechanism of GWZ721 magnesium alloy during extrusion

The solution treated GWZ721 (Mg-7Gd-2Y-1Zn-0.4Zr) magnesium alloy ingot was hot extruded at 400 °C to obtain T-shape profile. The metal rheological structure characteristics of different parts in the extruded ingot during extrusion deformation were studied by optical microscope (OM), scanning electron microscope (SEM), electron back scatter diffraction (EBSD), and so on. The results show that twin deformation occurs during extrusion loading, dynamic recrystallization occurs when the ingot enters the mold cavity, and static recrystallization occurs after extrusion. The average grain size is gradually refined, and the second phase is broken, refined and dispersed in the matrix. The texture with the base plane parallel to the extrusion direction is formed, and its maximum relative strength first becomes stronger and then weaker. The cross-section microstructure of trial-produced T-shape profile is uniform, the grain size is small, and there is weak basal texture.