【作者】 赵青才；

【导师】 严红革；

【作者基本信息】 湖南大学 ， 材料加工工程， 2008， 硕士

【摘要】 采用快速凝固/粉末冶金法制备镁合金时,可以显著细化合金的晶粒组织、减少甚至消除粗大的平衡析出相,从而显著提高合金的塑性变形性能和力学性能,这对高强高韧性变形镁合金材料的研制和工业化应用具有重要的意义。本论文利用实验室自行设计的雾化-双辊激冷装置制备了AZ91镁合金箔片状粉末,通过致密化和塑性变形的方法制备出了直径为Φ10mm和Φ8mm的AZ91镁合金材料;通过将合金粉末与SiC粉末均匀混合的方法制备出了SiCp/AZ91复合材料棒材。利用扫描电镜(SEM)、X-射线衍射(XRD)和透射电镜(TEM)等检测手段研究了快速凝固/粉末冶金AZ91镁合金及其复合材料的晶粒组织、析出相的演变规律,SiC增强颗粒在合金基体中的分布特点和材料的力学性能,探讨了材料的强化机制和拉伸断裂机理,研究了快速凝固/粉末冶金AZ91镁合金及其复合材料在各热处理过程中的微观组织及其力学性能的稳定性。研究结果表明,快速凝固/粉末冶金AZ91镁合金棒材组织由过饱和α-Mg相和少量细小的β-Mg17Al12相组成;合金粉末热挤压后的密度可达到理论值;快速凝固AZ91镁合金及其复合材料的理想挤压温度为350℃,挤压速度为0.1m/min。快速凝固AZ91镁合金挤压棒材的抗拉强度和伸长率分别为383.23MPa和9.4%;随着挤压比的增加,晶粒变得更加细小,从而提高了材料的抗拉强度、屈服强度和伸长率;热挤压AZ91镁合金在室温拉伸时呈现韧性断裂特征。采用快速凝固/粉末冶金法制备的SiCp/AZ91复合材料中SiC颗粒分布较均匀,复合材料的屈服强度、抗拉强度、伸长率随SiC颗粒含量的增加而逐渐减小。在热挤压过程中,Mg和SiC颗粒表面的SiO2之间发生了界面反应,在界面产生Mg2Si相。与合金材料相比,复合材料的力学性能有所下降。不同工艺参数条件下对快速凝固/粉末冶金AZ91镁合金及其复合材料棒材进行热处理研究,并对其组织和性能进行分析。实验表明,快速凝固/粉末冶金AZ91镁合金在退火处理过程中发生了静态再结晶现象,在200℃时可以观察到再结晶现象。分析了退火温度和退火时间对合金显微组织和硬度的影响规律。快速凝固/粉末冶金SiCp/AZ91棒材在退火处理过程中也发生了静态再结晶。更多还原

【Abstract】 Fabricating magnesium alloy by rapid solidification/powder metallurgy (RS/PM), can refine the grain of the alloy ,reduce and eliminate the coarse precipitation phase, and then improve the plastic forming properties and mechanical properties of the alloy. It is vital significance for developing high-strength and high elongation property wrought magnesium and industrial appliations.In this study, alloy fluid flow was broken up, the AZ91magnesium alloy powder was prepared by twin-roll rapid solidification technique, and then the hot extrusion of AZ91 alloy solid materials 10mm and 8mm in diameter were prepared at 350℃. The SiC powder and AZ91 alloy powder were blended uniformly and then SiCp/AZ91 magnesium matrix composites have been fabricated using rapid solidification/powder metallurgy (RS/PM) process. By means of SEM, XRD and TEM, some analysis on grain structure, the change of precipitation phase, the distribution of SiC particles in matrix and mechanical properties of materials was carried out. Reinforcing mechanism and tensile fracture behavior were discussed, and the stability of microstructure and mechanical property of RS/PM AZ91 magnesium alloy and RS/PM SiCp/AZ91 composites at different technological conditions of heat treatment were studied too.The experiment results showed that RS/PM AZ91 magnesium alloy microstructures consist dominantly of supersaturatedα-Mg solid solution and little amount of the fine Mg17Al12 phase. The density of the hot-extruded RS AZ91 powder was approximately near the theoretical density of alloy. The optimal extrusion temperature and extrusion speed of RS/PM AZ91 magnesium alloy and its composites was 350℃×0.1m/min. The ultimate tensile strength of the as-extruded AZ91 alloy was 383.23MPa, the elongation was 9.4%. Increasing the extrusion ratio could refine the grains and improve the yield, tensile strength and elongation of the as-extruded AZ91 alloy. The as-obtained alloy shows ductile fracture feature.The silicon carbide particulates(SiCp)in AZ91 magnesium alloy metal matrix were near uniformly dispersed through the alloy matrix. The mechanical properties of the composite such as tensile strength, yield strength and elongation degraded with the increase of the content of SiCp. The Mg2Si appeared to originate between the Mg and SiO2 on the surface of SiC during the hot extrusion. For all content of the SiC particle reinforcement the mechanical properties of the composite was lower than the unreinforced counterpart.Heat treatment of RS/PM AZ91 magnesium alloy and its composites under different processing parameter was studied, then the microstructure and mechanical properties were analyzed. the results showed that the occurrence of static recrystallization in magnesium alloy bars during annealing can be observed, which began at annealing of 200℃. The influencing mechanism of annealing temperature and annealing time on the microstructure and hardness of the alloy bars were approached. The occurrence of static recrystallization in RS/PM SiCp/AZ91 composites bars during annealing could be observed too.更多还原