【作者】 李爱文；

【导师】 罗承萍；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2010， 硕士

【摘要】 本文综述了镁合金的特点、应用现状及发展方向,介绍了Mg-Zn系合金的研究进展。利用显微硬度计、光学显微镜、X-射线衍射仪、扫描电子显微镜和透射电子显微镜等手段分析和讨论了Mg-3Zn-xCu-0.6Zr镁合金的显微组织特征和时效析出行为以及固溶时效处理和合金元素Zn、Cu对其时效行为的影响。铸态Mg-3Zn-xCu-0.6Zr镁合金显微组织主要由Mg（六方晶系）基体和沿晶界分布的共晶组织（Mg+Mg2Cu+CuMgZn）组成,其中的Mg2Cu（正交晶系）与CuMgZn（四方晶系）呈块状。这类共晶组织在合金的铸造过程中起抑制晶粒长大的作用。随Cu含量的增加,合金晶界上形成的共晶组织增加,平均晶粒尺寸减小。440℃/24h固溶处理后,晶界处大部分非平衡共晶组织溶解,致使晶界组织明显减少,变得纤细,呈不连续状。440℃/24h固溶和180℃时效处理后Mg-3Zn-xCu-0.6Zr镁合金的析出相主要有三类:（1）大量弥散分布的板条状或四棱柱状β₂′-MgZn₂,轴线垂直于（0001）Mg;（2）合金A（0.5wt.%Cu）中还析出较多粗大的六棱柱状β₂′-MgZn₂相,其轴线也与基面（0001）Mg垂直;（3）Cu含量小于1.0wt.%时（合金A）,合金晶内还析出较多板条状和针状相β-MgZn,其轴线平行于（0001）Mg,合金B（1.0wt.%Cu）中也有少量β-MgZn相析出。其中板条状和棱柱状β₂′-MgZn₂是合金时效强化相的主体。此外,未发现G.P.区的存在。合金基体内生成其晶体学与形变孪晶相同的相变孪晶,孪晶面为{10（1|-）2}。不同Cu含量的Mg-3Zn-xCu-0.6Zr镁合金180℃时效硬化曲线都显示:基体的显微硬度值随时效时间的延长而呈现先增大后减小的趋势,其中合金C（1.5wt.%Cu）时效硬化效应最强,时效16h达到时效硬度峰值HV65.12。Cu的加入,一方面提高了合金的固溶温度,提高了固溶处理后合金中的空位浓度;同时Cu的存在增强了Cu、Zn与空位之间的相互结合作用,使淬火后空位能有效的保留下来,因而显著促进了析出相的空位形核和析出密度。含Cu越多（Cu<2.0wt.%）,析出相的数量越多、分布越弥散,晶内时效硬化效应越强。另一方面,Cu的加入还能有效促进Zn在镁基体中的扩散,因此,随Cu含量的增加,β₂′-MgZn₂增加,Zn的消耗增加,因而β-MgZn相应减少。Cu>1.0wt.%时（合金C和合金D）,合金晶内几乎没有β-MgZn相析出。更多还原

【Abstract】 The features, applications and developing trends of Mg alloys were reviewed, and the progress in Mg-Zn alloy research was summarized. The microstructure and precipitation behavior of the Mg-3Zn-xCu-0.6Zr magnesium alloy, as well as the effects of the heat treatment and alloy elements Zn, Cu on the precipitation behavior of the alloy were investigated by means of microhardness tester, optical microscopy （OM）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）.The microstructure of the as-cast Mg-3Zn-xCu-0.6Zr was composed of the Mg matrix （HCP）, eutectic （Mg+Mg2Cu+CuMgZn） formed at grain boundaries, in which the block-shaped Mg2Cu （orthorhombic） and CuMgZn （tetragonal） eutectic components were alternatively distributed within the Mg matrix. The eutectic played a role in inhibiting grain growth during casting. With increasing the Cu content, the eutectic increased and the average grain size reduced accordingly. After solution treatment at 440℃, a majority of the nonequilibrium eutectic were dissolved, with grain boundary microstructure becoming thin and discontinuous.Three types of precipitates were formed by 440℃solution treatment and 180℃aging of the alloy. The first one was a high-density, lath-like or prismaticβ₂′-MgZn₂ with a length of 50nm²00nm, which was perpendicular to the base plane （0001）Mg of the Mg matrix and served as the principal strengthening phase of the aged alloy. The second one was a plate-likeβ₂′-MgZn₂, observed in alloy A （0.5wt.%Cu）, which was also perpendicular to the base plane of the Mg matrix. The third one was the short-lath like or needle-likeβ-MgZn, a large amount in alloy A, and with an average length of about 50nm¹50nm and its axis parallel to the base plane of the Mg matrix. A small amount of this precipitate was also found in alloy B （1.0wt.%Cu）. Besides, no plate-like G.P. zones were detected at the temperature investigated. {10（1|-）2} growth twin, with the same crystallographic orientation as that the deformation twin, were observed in the cast Mg-Zn-Cu magnesium alloys.The age-hardening profiles of the solution treated and aged Mg-3Zn-xCu-0.6Zr magnesium alloy with different Cu content showed such a hardening tendency of the alloyes that the micro-hardness was first increased and then decreased with increasing the aging times at 180℃and reached a maximum of HV65.12 at 16 hours in alloy C （1.5wt.%Cu）. The addition of Cu, on the one hand, can enhance the solution treatment temperature for the alloys thus increasing the density of the vacancy which was supposed to play a crucial role in the precipitate nucleation and the presence of Cu also enhanced the positive interaction between the Cu or the Zn atoms and vacancies in the Mg matrix, hence in increasing the precipitation density. With increasing the Cu content up to 2.0wt%, the quantity and precipitation density ofβ₂′-MgZn₂ increased, the peak hardness increased. On the other hand, Cu can promote the diffusivity of Zn in the Mg matrix, therefore facilitating the nucleation and growth of the precipitates. The amount ofβ-MgZn, decreased with increasing the Cu content due to the depletion of Zn brought about by the favored formation ofβ₂′-MgZn₂. When Cu content beyond 1.0wt.%, e.g. alloy C and alloy D, there was almost noβ-MgZn precipitates.更多还原