【作者】 张俊远；

【导师】 周禾丰； 王社斌；

【作者基本信息】 太原理工大学 ， 材料学， 2008， 硕士

【摘要】 镁合金具有密度低、比强度和比刚度高、阻尼性能好以及电磁屏蔽能力强等优点,近年来成为汽车和电子行业的重要轻质材料,被誉为21世纪最具有发展潜力的“绿色工程材料”。随着汽车轻量化的要求,越来越多的汽车零部件采用镁合金制造来减轻汽车自重,其中汽车轮毂对于汽车减重具有尤其重要的意义和效果,但轮毂的使用条件决定其必须同时具有较高的强度和韧性,目前的镁合金材料还达不到这方面的要求。AM60及AZ91镁合金是工业应用最为广泛的镁合金。AM60韧性较好,但强度有待进一步提高。提高镁合金的强韧性是拓展镁合金在汽车上的应用范围的一个重要方向。针对目前应用广泛的AM60镁合金,经合金设计过程确定目标合金成分后,本研究采用真空电阻熔炼炉在Ar保护条件下添加合金元素对其进行精炼,并得到了所需的合金试样。利用火花原子放射光谱仪、等离子体光谱仪、X射线衍射仪、金相显微镜、带能谱的扫描电镜、拉伸试验机等手段,分析、研究了合金添加剂对合金组织性能的影响,并探讨了其对合金组织性能影响的机理。通过试验与分析,得出以下结论:1)在AM60合金中添加稀土Nd后,引起了合金组织的显著变化,晶粒明显细化,网状β-Mg₁₇Al₁₂相变为断续、弥散分布的骨骼或颗粒状。同时合金中开始出现杆状Al₁₁Nd₃新相。随着稀土含量的增加,β-(Mg₁₇Al₁₂)相数量减少、尺寸变小,而Al₁₁Nd₃相则增多变粗。AM60合金的力学性能随着稀土含量的增加而增加。当稀土含量达到0.9wt%时,抗拉强度σ_b、屈服强度σ_0.2、延伸率σ均达到较高值,其值分别为230MPa、127MPa和14%,进一步增加稀土含量则有所下降。以上变化主要是由于晶粒细化、第二相强化以及固溶强化等相互协调作用的结果。2)在AM60合金中加入变质剂C元素后,发现C元素主要分布在AlMn相和β相中,基体中很少有C元素的存在。C元素能够增加了合金凝固过程中的过冷度,细化合金组织,提高了合金性能。因加入C元素的形态不同,其对合金组织性能的影响按石墨粉、原煤粉、C纤维的顺序依次增大;即C纤维对合金组织的细化效果最为显著,室温力学性能的提高最为显著,其抗拉强度和延伸率分别达到了242.4MPa和13.2%,比基体合金分别提高了23%和2.5倍。3)AM60合金的断裂方式为解理断裂和准解理断裂,而添加剂（C或Nd）的加入使合金断口出现些微观塑性特征,说明合金的塑性得到了提高。更多还原

【Abstract】 Magnesium alloy has the advantages of light-weight, high strength/weight ratio, high stinffess/weigh ratio, high damping property and electromagnetism shielding property and so on. It has bright promise to be widely used in aviation and spaceflight, vehiele, eleetrommunieation, and is regarded as the most promising green material of the 21st century. Following with the light-weight of automobiles, more and more automobiles" components are made from magnesium alloys, where the wheels have a special magnificence and effect on the weight-save of automobiles. But Wheels should have both high strength and high toughness depending on their working environment, the magnesium alloys at present has not satisfied the requirement yet. AM60 and AZ91 are the most broadly used magnesium alloys in industry. AM60 alloy has a high ductility but its strength need to be improved.In this paper, a vacuum resistant melting furnace was used to refine AM60 magnesium alloy. By addition of different amount of alloy additive, specimens for testing were cast out of the melted metals. By using atomic Emission Spectrometry, ICP Spectrometry, XRD, metallographic microscopy, SEM and so on, the microstructure and propertities of AM60 were analyzed, and the mechanism is discussed. The main conclusions are as follows:1) Nd is important alloying element to magnesium alloys. With additions of Nd, the microstructure of as-cast magnesium alloys AM60 alloy were refined obviously.A rod-like inter metallic phase Al₁₁Nd₃ phase was observed and the volume of theβ-phase(Mg₁₇Al₁₂) somewhat decreased.More Nd addition caused further decreasing of theβ-phase and coarsening of Al₁₁RE₃. RE improved hardness and tensile properties of AM60 alloys. The ultimate tensile strength,yield strength and elongation of alloys with 0.9wt% addition of RE reached a high value, maximum tensile strength, maximum yield strength, maximum elongation are 230MPa, 127MPa and 14% respectly, and then decreased with more Nd additions.That’s all caused by the wafer skilled、the second phase reference and the increase on volume and quantity of the new phase Al₁₁Nd₃.2) With additions of C into AM60 alloy, the C element was discovered mostly in the AlMn phase andβ-phase and hardly in theα-Mg phase.The C element can increase the undercooling of AM60 alloy during the solidification, so the microstructure of AM60 alloys were refined and the properties were improved. Because of different forms of C, the effects on the AM60 alloy were increased the order by graphite, coal, C fibre. The mechinacal tests incate that AM60 has the best microstructure and properties when the form of the C is C fibre.Maximum tensile and maximum elongation are 242.4Mpa and 13.2% respectively,increased by 23% and 2.5 times respectly.3) Form of failure of magnesium alloy is usually brittle through cleavage or quasi-cleavage fracture. Fracture of alloys have more characteristics of microcosmic ductility with C or Nd addition, which indicates that the addition of C or Nd can improve the ductility of AM60 alloy.更多还原