基于等径角挤压（ECAP）的超细晶铸造镁合金制备研究

研究了铸造镁合金等径角挤压（ECAP）的原理与技术实施手段.通过设计ECAP模具的几何结构,研究了剪切应变累积效应的度量方法.通过对AM60镁合金铸锭单道次ECAP加工后光学显微组织的观察,讨论了模具几何结构条件（转角与背转角大小）对变形组织演化形态的影响.根据多道次ECAP试验的位移-挤压力关系曲线,考察了加工工艺条件（加工道次数、背压与加工速率）对变形组织形态的影响规律.分析了镁合金ECAP加工技术的试验和模拟方案.研究表明：AM60镁合金铸锭的ECAP变形组织形态较好地符合理论预测结果;多道次ECAP加工显著改善了AM60镁铸锭的微观组织;对于具有粗大晶粒的铸造镁合金而言,ECAP工艺能以机械化冶金方式制备其超细晶结构.

Preparation of Ultra-Fine Grained Cast Magnesium Alloy by Equal Channel Angular Pressing

In the present work, the principles and processing modes of equal channel angular pressing (ECAP) for as-cast magnesium alloys were investigated. With structural design of ECAP die, the accumulated effect of shear strains under ECAP was calculated. By observation of optical microstructure of single-passed ECAP deformed cast ingot of AM60 magnesium, the effective relationship of die geometric structure (angle and subtending one at corner between entry and exit channels) to the evolution of deformed microstructure was discussed. Based on the curves of displacement versus extrusion force during multi-passed ECAP, a mode of evolution of deformed microstructure was analyzed under different pressing conditions (e.g. number of passes, back-forces, and deforming rate). Routine of experiment and modeling for ECAP of magnesium alloys was schemed. It can be concluded from the study that the ECAP deformed microstructure of AM60 casting ingot fits the one estimated by theory of plastic mechanics well. Multi-passed ECAP can perfect the microstructure of alloy tremendously. For as-cast magnesium alloys characterized by coarse-grained structure, ECAP is an effective thermo-mechanical processing to make their ultra-fine grains.