【作者】 曾强；

【导师】 王丽娟；

【作者基本信息】 南昌大学 ， 机械工程， 2022， 硕士

【摘要】 铝及铝合金具有密度低、耐腐蚀性能好和易于成型等优点,在航空航天、交通运输和医疗器械等工业领域内复杂异形零部件的制造中已有极其广泛的应用。由于增材制造技术的设计自由和快速成型等优势,采用选区激光熔化(Selective Laser Melting,SLM)技术制造铝及铝合金构件的应用研究也越来越多,但是关于SLMAlSi10Mg的微观结构演化机理还缺乏相应的了解,基于此,本文采用分子动力学(Molecular Dynamics,MD)的方法研究了SLMAlSi10Mg的力学性能。本文具体研究内容如下:(1)采用了EAM多体势对SLM铝的力学性能进行了分子动力学模拟。主要考察了不同晶态、温度和柱状晶晶粒取向对SLM铝力学性能的影响。结果表明,SLM铝柱状晶在不同温度下的抗拉强度低于单晶铝,但大于等轴晶铝。随着温度的升高,抗拉强度和杨氏模量均近似线性下降。单晶的主要变形机制为堆垛层错形成和非晶化,而等轴晶和柱状晶的主要变形机制为位错滑移、晶界迁移和扭转。最后,研究了柱状晶晶粒取向对力学性能的影响,发现杨氏模量几乎与晶粒取向无关,抗拉强度受到柱状晶晶粒取向的影响很大。合理控制晶粒取向可以提高SLM铝的抗拉强度。(2)运用EAM多体势研究了纳米孪晶与Fe掺杂对分子动力学模型SLM铝力学性能的影响。结果表明,在不同晶态铝中插入纳米孪晶,可以提高单晶铝的抗拉强度,但降低了等轴晶和柱状晶铝的抗拉强度。其中,柱状晶的力学性能对孪晶最敏感,抗拉强度受到影响程度最大。孪晶界间距(λ)对柱状晶铝强度的影响存在临界值(2.8 nm),当λ小于2.8 nm时,柱状孪晶铝的抗拉强度随着λ增加而减小,当λ大于2.8 nm时,柱状孪晶铝的抗拉强度随着λ增加而逐渐增加,直到接近无孪晶柱状铝的强度。与不同晶态孪晶铝的强度相比,掺杂5 at.%Fe的不同晶态孪晶铝的强度更大,且柱状孪晶Al-5%Fe的强化效果最好,合理控制Fe含量和纳米孪晶形态,有望改善SLM铝的力学性能。(3)通过EAM势、ADP势以及LJ势混合的混合势研究了纳米裂纹对分子动力学模型单晶/柱状晶SLMAlSi10Mg拉伸力学性能的影响。结果表明,相比与无裂纹模型,裂纹宽度较小时,材料的强度影响很小。研究结果还发现,不同纳米裂纹生长位置力学性能差异较大,合理控制裂纹生长位置,可以改善材料的力学性能。同时还考察了温度对预制纳米裂纹的单晶/柱状晶力学性能的影响,发现随着温度的升高,抗拉强度和杨氏模量的降低速率在逐渐增加,且抗拉强度降低程度最大。更多还原

【Abstract】 Aluminum and aluminum alloys have the advantages of low density,good corrosion resistance and easy forming,and have been widely used in the manufacture of complex and special-shaped parts in aerospace,transportation,medical equipment and other industrial fields.Due to the advantages of additive manufacturing technology such as freedom of design and rapid prototyping,the application of selective laser melting(SLM)technology for manufacturing aluminum and aluminum alloy components has been increasingly studied,but the microstructure evolution mechanism of SLMAlSi10 Mg is not yet understood.In this paper,the mechanical properties of SLMAlSi10 Mg are investigated by molecular dynamics(MD).The details of this paper are as follows.(1)The EAM multi body potential is used to simulate the mechanical properties of SLM aluminium.The effects of different crystalline states,temperatures and grain orientation of columnar grains on the mechanical properties of SLM aluminium are mainly investigated.The results show that the tensile strength of SLM aluminium columnar crystals at different temperatures is lower than that of single-crystal aluminium,but greater than that of equiaxed grains aluminium.The tensile strength and Young’s modulus both decrease approximately linearly with increasing temperature.The main deformation mechanisms for single crystals are stacking fault formation and amorphisation,whereas the main deformation mechanisms for equiaxed and columnar grains are dislocation slip,grain boundary migration and torsion.Finally,the effect of grain orientation on the mechanical properties of columnar crystals is investigated,and it is found that Young’s modulus is almost independent of grain orientation.The tensile strength is greatly influenced by the grain orientation of columnar grains.The tensile strength of SLM aluminium can be improved by rational control of grain orientation.(2)The effect of nano-twin and Fe doping on the mechanical properties of SLM aluminium is simulated MD simulations with the EAM multibody potential.The results show that the insertion of nano-twins in different crystalline aluminum can increase the tensile strength of single crystal aluminum,but reduce the tensile strength of equiaxed grains and columnar grains aluminum.Among them,the mechanical properties of columnar grains are the most sensitive to twins,especially the tensile strength.There is a critical value of 2.8 nm for the effect of twin boundary distance λ on the tensile strength of the columnar crystal aluminum.Whenλ is less than this value,the tensile strength of columnar twin aluminum decreases with the increase of λ,while when λ is greater than this value,the tensile strength of columnar grains aluminum gradually increases with the increase of λ,until it is close to that of columnar grains aluminum with twin-free.Compared with the tensile strength of different crystalline twin Al,the tensile strength of different crystalline twin Al doped with 5 at.% Fe is greater,and the strengthening effect of columnar twin Al-5%Fe is the best,indicating that reasonable control of the content of Fe and nanotwinned crystalline,which are expected to improve the mechanical properties of SLM aluminum.(3)The effect of nanocrack on the tensile mechanical properties of single-crystal/columnar grains SLMAlSi10 Mg is investigated using MD simulations with a mixture of EAM potential,ADP potential and LJ potential.The results show that when the crack width is smaller,the strength of the material has little effect compared to the free-crack model.It is also found that the mechanical properties of different nanocrack growth locations are quite different,and the reasonable control of crack growth locations can improve the mechanical properties of the material.At the same time,the effect of temperature on the mechanical properties of single crystal/columnar crystal of prefabricated nanocrack is also investigated.It is also found that as the temperature increased,the decreasing rate of tensile strength and Young’s modulus increase gradually,and the decrease of tensile strength is the largest.更多还原