【作者】 陈曦；

【导师】 孟令刚；

【作者基本信息】 大连理工大学 ， 机械， 2023， 硕士

【摘要】 大锻件在国防民生中有至关重要的作用。目前大锻件制造需要使用体积更大的铸件进行锻压成型,造成极大的浪费。同时,大铸件生产中的尺寸效应,偏析、气孔等缺陷严重。金属构筑成形技术是采用高质量小型基元,通过表面加工清洁,真空封装,经扩散预连接后锻造成形,得到大断面锻件。目前已经成功实现ODS钢构筑成形的界面愈合,但是应用在铝合金时,受表面致密稳定氧化膜的阻碍,实现铝合金界面完全愈合亟需开展更多的基础研究。本课题利用金属构筑成形技术,研究2219铝合金以及其他体系铝合金同质连接工艺,希望通过合金元素冶金反应和塑性变形以及表面处理等工艺促进界面氧化物分解扩散,实现界面愈合及均质化。对于2219铝合金界面愈合工艺进行研究,改变表面处理方式和在保温过程中施加塑性变形。结果表明:800#砂纸打磨和酸洗结合,可以获得合适的待连接表面,减少界面孔洞缺陷,增加界面区域的塑性变形,易于破碎氧化物;随着塑性变形量由10%开始增加,界面强度逐渐升高,界面愈合过程中,局部塑性变形使条状缝隙被隔断,界面氧化物分解扩散,Al₂Cu相向界面偏聚破碎氧化膜,填充孔洞缺陷,但其对界面的钉扎作用,阻碍再结晶和界面迁移,残留在Al₂Cu相中的氧化物难以分解扩散。545℃保温4h时变形量50%时界面强度最高为116MPa。为了探究航天用铝合金中常见的Cu、Zn和Mg元素对界面愈合的影响,改变扩散连接温度、保温时间和塑性变形量。结果表明:不同合金元素在铝合金中的存在形式不同,对界面愈合造成不同的影响。Cu元素在Al-5.4%Cu二元铝合金中形成较为稳定Al₂Cu相,随着温度由500℃升高到545℃,界面偏聚的Al₂Cu相增多,挤压破碎氧化膜,保温时间的延长和塑性变形量增加,增强界面处的再结晶和界面迁移,界面强度在545℃保温4h塑性变形50%时达到最高114MPa,但Al₂Cu相钉扎界面,阻碍再结晶和界面迁移,使界面难以完全愈合;Zn元素在Al-5.56%Zn二元铝合金中形成有序固溶体,造成基体点阵晶格畸变加剧,随着温度升高和保温时间的延长,更多的Zn原子在界面形成富集,形成的晶格畸变与微区塑性变形形成的位错等缺陷共同作用,促进Zn原子的体扩散和氧化物的分解,在塑性变形作用下,界面处的再结晶改善界面愈合,虽然氧化物仍沿界面分布明显,但界面强度升高,在480℃保温4h变形量50%时最高为61MPa。Mg元素与其他合金元素形成新的析出相,熔点较低Al-5.4%Cu-1.2%Mg三元共晶液相在较低温度下挤压破碎氧化膜,填充孔洞缺陷,包裹部分残留氧化物,对界面的钉扎作用弱,再结晶和界面迁移随着温度升高和塑性变形增大而越显著,界面强度最高位133MPa;在Al-5.56%Zn二元合金中,形成Mg Zn₂白色析出相颗粒,填充孔洞缺陷,在界面处偏聚,起到弥散强化的作用。除形成析出相外,Mg元素与氧化物直接发生冶金反应,生成细小的共晶产物,改善界面愈合。更多还原

【Abstract】 Large forgings play a vital role in national defense and people’s livelihood.At present,the manufacture of large forgings requires the use of larger castings for forging forming,resulting in great waste.At the same time,the size effect,segregation,porosity and other defects in the production of large castings are serious.The metal building forming technology is to use high-quality small elements,clean through surface processing,vacuum packaging,and forging after diffusion pre-connection to obtain large-section forgings.At present,the interface healing of ODS steel has been successfully realized.However,when it is applied to aluminum alloy,it is hindered by the dense and stable oxide film on the surface.It is urgent to carry out more basic research to realize the complete healing of aluminum alloy interface.In this thesis,the homogeneous bonding process of 2219 aluminum alloy and other systems of aluminum alloy is studied by using metal construction forming technology.It is hoped that the decomposition and diffusion of interfacial oxides can be promoted by metallurgical reaction of alloying elements,plastic deformation and surface treatment to achieve interface healing and homogenization.The interface healing process of 2219 aluminum alloy was studied by changing the surface treatment method and applying plastic deformation during the heat preservation process.The results show that the combination of 800#sandpaper grinding and pickling can obtain a suitable surface to be connected,reduce the interface hole defects,increase the plastic deformation of the interface area,and easily break the oxide.As the plastic deformation increases from 10%,the interface strength gradually increases.During the interface healing process,the local plastic deformation separates the strip gap,and the interface oxide decomposes and diffuses.The Al₂Cu phase segregates to the interface and breaks the oxide film,filling the hole defects.However,its pinning effect on the interface hinders recrystallization and interface migration,and the oxide remaining in the Al₂Cu phase is difficult to decompose and diffuse.The highest interfacial strength is 116 MPa when the deformation is 50%at 545°C for 4h.In order to explore the effects of common Cu,Zn and Mg elements in aerospace aluminum alloys on interface healing,the diffusion bonding temperature,holding time and plastic deformation were changed.The results show that different alloying elements have different forms in aluminum alloy,which have different effects on interface healing.The Cu element forms a relatively stable Al₂Cu phase in the Al-5.4%Cu binary aluminum alloy.As the temperature increases from 500°C to 545°C,the Al₂Cu phase segregated at the interface increases,and the oxide film is squeezed and broken.The extension of holding time and the increase of plastic deformation enhance the recrystallization and interface migration at the interface.The interface strength reaches a maximum of 114 MPa when the plastic deformation is 50%at 545°C for 4h.However,the Al₂Cu phase pins the interface,hinders recrystallization and interface migration,making the interface difficult to heal completely.The Zn element forms an ordered solid solution in the Al-5.56%Zn binary aluminum alloy,which causes the lattice distortion of the matrix lattice to increase.As the temperature increases and the holding time increases,more Zn atoms form an enrichment at the interface.The lattice distortion and dislocations formed by micro-area plastic deformation work together to promote the bulk diffusion of Zn atoms and the decomposition of oxides.Under the action of plastic deformation,the recrystallization at the interface improves the interface healing.Although the oxides are still distributed along the interface,the interface strength increases.When the deformation is 50%at 480°C for 4h,the maximum is 61MPa.The Mg element forms a new precipitated phase with other alloying elements.The Al-5.4%Cu-1.2%Mg ternary eutectic liquid phase with lower melting point squeezes and breaks the oxide film at a lower temperature,fills the hole defects,and encapsulates some residual oxides.The pinning effect on the interface is weak,and the recrystallization and interface migration are more significant with the increase of temperature and plastic deformation.The highest interface strength is 133 MPa.In Al-5.56%Zn binary alloy,Mg Zn₂ white precipitates are formed.更多还原