【作者】 曹特；

【导师】 陈振华；

【作者基本信息】 湖南大学 ， 材料加工工程， 2010， 硕士

【摘要】 镁基复合材料具有密度低、比强度高、比刚度高,以及良好的尺寸稳定性等优异性能,在诸多领域具有广阔的应用前景。快速凝固／粉末冶金(RS／PM)为制备颗粒增强金属基复合材料的重要方法之一。本文采用雾化-双辊急冷法制备了Si添加量不同的快速凝固AZ91粉末,然后把粉末通过热挤压制备成复合材料。研究了不同Si添加量对合金薄片的微观组织和时效硬化行为的影响,不同Si的添加对复合材料的显微组织,室温和高温力学性能,高温蠕变性能的影响,得到以下结论：1、采用雾化-双辊急冷法制备出了原位生成Mg2Si增强相的(1wt%Si)A1合金、(3wt%Si)A2合金、(5wt%Si)A3合金薄片。3种合金薄片均为细小等轴晶和部分蔷薇状的微细枝晶组成,其晶粒大小为1μm～3μm。随着Si添加量的增加,晶粒大小没有明显的变化。对三种合金薄片的热处理后发现,在473K和523K下热处理时,合金在60min时出现峰值时效。而在573K下的热处理时,在30min时硬度值就已接近峰值。其中A3合金薄片在473K下保温1h时拥有最高的硬度值为118.02HV。2、合金挤压板材的显微组织发生明显变化,晶粒明显增大,约为5～15μm。随着Si添加量的增加,合金中原位生成的Mg2Si颗粒逐渐长大。Si的加入后合金表现出优异的力学性能,其平均抗拉强度相比基体提高了约18%。合金的断裂延伸率随Si添加量的增加而下降,而A1合金相比基体合金断裂延伸率有了一定的提高。在室温下,A2合金具有最佳的力学性能,其6b最高可达472MPa,σ0.2、δ分别达到329MPa、4.70%。在高温下(473K),合金的抗拉强度随着si添加量的增加而增加,其中A3合金的抗拉强度达到了192MPa。合金在523K的抗拉强度下降迅速,都在90MPa左右。室温下A1和A2合金的断裂方式以韧性断裂为主,A3合金呈现了复合性断口特征,有撕裂棱的韧性断裂特征,同时也存在少量脆性断裂的解理痕。在断口上都发现了增强体Mg2Si明显被拉断的痕迹。3、研究了Si对RS／PM(AZ91)合金的抗蠕变性能的影响。发现在150℃／50MPa的蠕变条件下,A1合金的稳态蠕变速率相比基体有明显下降,约为基体的1／5,A2合金的稳态蠕变速率约为基体的1／8,A3合金的稳态蠕变速率约为基体的1／18。三种合金在(423K-473K)／(50MPa-90MPa)的实验条件下合金的蠕变机制为受扩散控制的位错攀移机制。更多还原

【Abstract】 Magnesium alloy matrix composites have great potential for applications in a good many fields due to its low density, high specific strength and good dimension stability, etc. Rapid solidification/Powder metallurgy(RS/PM) is an important method to prepare particle reinforced metal matrix composites (MMCs). Different Si content enhanced AZ91 magnesium alloy powders were prepared through atomization-twin rolls quenching technology in the present dissertation, then the powders were consolidated into composite materials by hot extrusion The effects of different Si addition on the micro structures and age-hardening behavior of the alloy flakes were investigated. And the effects of different Si addition on microstructures, room and elevated temperature tensile properties, elevated creep properties of alloys were investigated. The conclusions are drawn as follows:1. Al(1wt%Si+AZ91)、A2(3wt%Si+AZ91)、A3(5wt%Si+AZ91) magnesium alloy flakes reinforced by in situ Mg2Si were prepared by atomization- twin rolls quenched technology. The three kinds of alloy flakes all exhibited fine equiaxed grains with the grain size of 1～3μm. And the grain sizes have no remarkably difference with the Si contents increased. After the hot treatment of the flakes, we found that, as aging at 473K and 523K for 60min, the value of microhardness reached maximum. When aging at 573K, the value of microhardness reached maximum in 30min. A3 alloy flakes had the topmost microhardness of 118.02HV after aging for 60min at 473K.2. After the process of extrusion, the microstructure of the alloy has changed significantly. The as-extruded materials exhibited equiaxed grains with the size of 5～15μm. Mg2Si particles generated in situ were grew up gradually as the increasing of Si content. By adding Si to alloy can significantly improve the mechanical properties. The average tensile strength compared to the matrix increased by about 18%. The fracture elongation of alloys decreased with the Si contents increasing. While compared to matrix, the fracture elongation of A1 alloy had a certain increase. At the room temperature, A2 alloy exhibits the best mechanical properties, its 0.2% yield tensile strength,ultimate tensile strength and elongation of rupture were 329MPa, 472MPa and 4.70%. Respectively, the alloy elevated temperature (473K) tensile properties improved as the Si addition increasing, and the tensile strength of A3 alloy reached to 192MPa. While at 523K, all of the alloys tensile strength decreased rapidly, were 90MPa around. The fracture characterization of A1 and A2 alloy exhibited ductile rupture at room temperature. A3 alloy presents the characteristics of compound fracture. The reinforcements Mg2Si were pulled off obviously in the fracture.3. By studying the effects of Si addition on RS/PM(AZ91) alloy elevated temperature creep resistance, found that under the conditions of 150℃/50MPa, the steady-state creep rate of Al alloy was markedly decreased compared to the matrix, is about 1/5 to the matrix. The steady-state creep rate of A2 alloy is of about 1/8 to the matrix. And A3 alloy is 1/18 to the matrix. The creep mechanism of the alloy are controlled by diffusion and dislocation climb mechanism under the experimental conditions of (423K-473K)/(50MPa-90MPa)更多还原