【作者】 陈伟；

【导师】 张诗昌；

【作者基本信息】 武汉科技大学 ， 材料加工工程， 2009， 硕士

【摘要】 镁合金具有密排六方晶体结构,滑移系少,塑性变形能力差。超塑性是提高镁合金塑性的一种重要方法。本文以AZ31镁合金为对象,研究了该合金在超塑性变形过程中的一些基础问题。失稳是材料超塑性拉伸变形的一种常见现象,超塑性拉伸失稳和普通拉伸失稳有明显不同。根据几何失稳判据推导出恒应变速率拉伸时几何失稳的应力条件。试验研究了温度和应变速率对AZ31镁合金超塑性拉伸载荷失稳以及几何失稳的影响。研究结果表明:载荷失稳以及几何失稳的临界应变量均随温度升高或应变速率降低而增加,几何失稳的临界应变大于载荷失稳的临界应变。即超塑性拉伸出现载荷失稳时并不立刻出现几何失稳,而是经历一段均匀变形后才开始出现几何失稳。应变速率敏感指数m是衡量超塑性的重要指标,一般通过实验得到。本文根据超塑性拉伸断面收缩的一般特点,引入了一个表征超塑性断面收缩特性的参数K,并建立了K与材料参数和变形参数的关系,用来衡量材料的超塑性。空洞是超塑性变形过程中必然产生的一种结构形态,对材料的超塑性有重要影响,对空洞数量的测量具有实际意义。基于超塑性拉伸的加工硬化与再结晶软化处于动态平衡的假设,本文提出一种根据材料拉伸曲线测量空洞分数的新方法。更多还原

【Abstract】 Magnesium alloy has hexagonal close-packed (HCP) structure,very limted slips and poor plastic deformation ability. Superplasticity is an important method to improve plasticity of magnesium alloy. In this paper, some basic issues on the superplastic deformation process of AZ31 magnesium alloy was investigated.Instability is a common phenomenon in the superplastic tensile deformation, superplastic tensile instability and the general instability are significantly different. According to the geometric instability criterion ,the critical stress of geometric instability was deduced under the conditions of superplastic tensile with constant strain rate; The effect of temperature and strain rate on load instability and the geometric instability of AZ31 magnesium alloy was experimental studied on the superplastic tensile. The results show that: critical strain of load instability as well as the geometric instability increase with temperature or strain rate decreases, the critical strain of geometric instability is greater than that of load instability. Superplastic tensile load Instability that does not appear immediately with geometric instability, but after going through a uniform deformation then the geometric instability began to emerge.Strain rate sensitivity exponent m is an important indicator of superplasticity and is general obtained through the experiments. By studying the changes of sections, a parameters K was putted forward to characterize the contractions of cross-section after superplastic tensile , and the relations of K with the material parameters and deformation parameters were established to measure superplasticity of materials. Cavitation is a structure in the process of superplastic deformation ,it has an important influence to superplasticity of the material, so the number of cavitation measurement is meaningful. Based on the hypothesis that work-hardening and the softening of recrystallization was in dynamic equilibrium when superplastic tensile, this paper presents a new method to measure cavitation exponent based on the material tensile curve.更多还原