【作者】 陈翔；

【导师】 陈哲；

【作者基本信息】 上海交通大学 ， 机械工程（专业学位）， 2021， 硕士

【摘要】 Al-Mg合金因其具有较高的比强度、良好的耐腐蚀性等优异的性能而被应用于交通运输制造和医疗设备等领域。但Al-Mg合金强度不高的缺点限制了其在尖端领域的发展和工业应用。学术研究中常利用加工硬化和第二相颗粒增强的策略来提高Al-Mg合金的强度。流动应力和加工硬化行为是由位错行为所主导的材料宏观力学行为的体现。合金材料的流动应力和加工硬化行为已经被广泛地研究和报告,然而对于颗粒增强的合金或者复合材料,这方面的研究却相对较少。研究表明,颗粒与位错之间的相互作用机制包括剪切机制和绕过机制,其对应的强化机制分别为剪切强化和Orowan强化。颗粒与位错之间不同的相互作用会对材料流动应力和加工硬化行为产生不同的影响,但这种影响的机制至今仍不清楚。因此,本文选取Al-Mg-Sc-Zr合金和Ti B₂/Al-Mg复合材料,分别研究了可剪切纳米析出相、不可剪切纳米析出相和不可剪切陶瓷颗粒对Al-Mg合金流动应力和加工硬化行为的影响。本文选取Al-Mg合金为基础研究合金,一方面引入Sc、Zr元素通过对时效条件的控制来得到不同Al₃（Sc,Zr）析出相增强的Al-Mg-Sc-Zr合金。另一方面通过原位自生法得到Ti B₂纳米陶瓷颗粒增强的Ti B₂/Al-Mg复合材料。首先,通过微观组织表征分析了Al-Mg-Sc-Zr合金中Al₃（Sc,Zr）析出相以及Ti B₂/Al-Mg复合材料中纳米陶瓷颗粒的形貌特征和分布情况。其次,通过实验和物理模型计算推导发现与基体共格的剪切析出相和不可剪切析出相以及与基体非共格的陶瓷颗粒对位错的增殖、分布、存储和湮灭都有着重要的影响。剪切析出相会促使位错产生平面滑移从而产生局部高位错密度的滑移带,这种滑移带的出现会导致位错的大量堆积和位错密度的增加;不可剪切析出相周围会产生Oworan位错环促进位错的存储与动态回复;Ti B₂颗粒周围则会诱导产生大量几何必需位错形成背应力强化。此外,本文还研究了应变速率对第二相颗粒增强的Al-Mg合金的流动应力和加工硬化行为的影响,通过定量表征材料变形过程中的位错密度,揭示了颗粒对加工硬化中动态回复速率的影响机制。本文集中研究了第二相颗粒增强的合金及复合材料的流动应力和加工硬化行为,并探索了颗粒与位错的相互作用,为理解第二相颗粒增强的合金及复合材料的力学行为提供了新见解,也为新型合金的设计提供了理论指引与思路。更多还原

【Abstract】 Al-Mg alloy is used in transport manufacturing and medical equipment due to its excellent properties like high specific strength and good corrosion resistance.However,the low strength of Al-Mg alloy limits its development and industrial applications in the frontier.In academic research,strategies like work hardening and second phase particle strengthening are often used to enhance the strength of Al-Mg alloy.Flow stress and work hardening behaviors are dominated by dislocation behaviors.The flow stress and work hardening behaviors of alloy materials have been studied extensively;however,the studies of alloys or composites reinforced by particles have been rarely reported.The particle-dislocation interactions contain shearing mechanism and bypassing mechanism,which corresponds to the shearing strengthening and Orowan strengthening.Different interactions between particles and dislocations have different effects on flow stress and work hardening behaviors of materials,but the mechanism of such effects is still unclear.Therefore,Al-Mg-Sc-Zr alloys and Ti B₂/Al-Mg composites were selected in this work to study the effect of nano shearable precipitates,nano non-shearable precipitates and non-shearable ceramic particles on flow stress and work hardening behaviors of Al-Mg alloy.In this work,Al-Mg alloy was selected as the basic research alloy.On the one hand,Sc and Zr elements were introduced to obtain Al-Mg-Sc-Zr alloys with different Al₃（Sc,Zr）precipitates by controlling the aging conditions;on the other hand,Ti B₂/Al-Mg composites reinforced by Ti B₂nano-ceramic particles were obtained by in-situ method.Firstly,the morphology and distribution of Al₃（Sc,Zr）precipitates in Al-Mg-Sc-Zr alloys and Ti B₂ nano-ceramic particles in Ti B₂/Al-Mg composites were studied by microstructure characterization.Then,the results of experiments and theoretical model show that the shearable and non-shearable precipitates and the ceramic particles have important effects on the dislocation multiplication,movement,storage and annihilation.Shearable precipitates leads to planar slip of dislocations and deformation band with higher local dislocation density,which brings a large amount of dislocation pile-ups and the increase of dislocation density.Lots of Orowan loops will accumulate around the non-shearable precipitates,and these accumulated Orowan loops could promote dislocation storage and dynamic recovery.Around Ti B₂ particles,a large number of geometric necessary dislocations（GNDs）that could promote back stress strengthening will be induced.In addition,this work also studied the influence of the strain rate on the flow stress and the working hardening behaviors of Al-Mg alloy reinforced by the second phase particles,and revealed the influence of the second phase particles on the dynamic recovery rate quantitatively by characterizing the dislocation density during deformation.In this paper,the flow stress and work hardening behaviors of the alloys and composites reinforced by the second phase particles are studied.The interaction between particles and dislocations is explored,which provides new insights for understanding the mechanical behaviors of alloys and composites reinforced by the second phase particles,as well as for designing new alloys and composites.更多还原