【作者】 刘贵立；

【导师】 李荣德；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2005， 博士

【摘要】 锌铝合金制造成本低,具有良好的使用与加工性能,显示出较好的应用前景和经济优势。然而,合金的高温性能差,易发生晶间腐蚀等缺点,限制了合金的进一步推广应用。为此,本文试图从理论角度探索改善锌铝合会及其复合材料的组织与性能的新方法、新途径,为合金及其复合材料的设计与制造提供参考依据。 通过自行开发软件建立了包括合金固体/液体相界、晶界在内的各种结构原子集团模型,采用递归法系统研究了ZA27合金中各元素的作用,组织细化机理,合金晶间腐蚀的原因及抑制方法。发现:过渡族元素能降低合金元素的扩散系数,提高α相的热稳定性:稀土元素富集在ZA27固体/液体相界,可使己凝固的α晶枝熔断并产生新核,从而细化晶粒:La、Y等稀土元素在α相晶界处减小Zn、Al的电极电位差,能够抑制晶间腐蚀,增强合金抗晶间腐蚀能力。 用有限元法分析SiC_p/ZA27复合材料在外载荷作用下基体与增强相界面应力场及基体内塑性应变规律,分析热残余应力场分布规律。结果表明:拉伸应力作用下界面法向应力引起极区基体与增强相脱粘:von Mises应力在极区与赤道区之间的界面处使基体屈服;增强相在残余应力作用下处于三向拉伸状态,容易发生脆性断裂:界面处残余法向应力较高,可能造成界面脱粘。基体内近界面残余切向应力具有抑制裂纹在基体中扩展的趋势。重载时复合材料在高温和高压应力共同作用下,基体发生严重的塑性流变,从而产生大量的纵横交错裂纹,并使增强相与基体在界面脱粘。增强相相对尺寸越大,基体内的塑性应变越小,即增强相能提高复合材料的抗塑性变形能力。 将人工神经网络与模拟退火算法相结合,解决了无解析关系式的复杂系统优化问题。提出了一种新的多目标函数优化模式,为解决同时提高合金多项力学性能问题提供了必要的手段。在此基础上预测合金力学性能并优化铸造工艺参数。更多还原

【Abstract】 ZA alloys have lots of advantages and economic predominance in engineering because of low cost and favorable machining properties. But their applications have been limited because of poor high temperature mechanical properties and corrosion resistance. Therefore, the purpose of this research is to find new methods and new approaches to improve the microstructure and properties of ZA alloys and their composites, which can provide guidance for the design and manufacture of the ZA alloys and their composites.Several atomic structure models including the interface between liquid and solid and the grain boundary were set up by using self-programed software. Recursion method was adopted to study systematically the effect of alloying elements in ZA27 alloys, the refinement mechanism of grain, the cause of corrosion along the grain boundary and the method of restraining corrosion in ZA alloys. The main results are: transition elements can reduce the diffusion coefficient of alloying elements, so they can heighten the high temperature stability of a phase. Rare Earth elements enriching on the interface between solid and liquid of ZA27, make the solidified dendrite arm melting and forming new nucleus, so the grains can be refined. La and Y elements can reduce the charge transfer between Zn and Al atoms over the grain boundaries, which decreases the difference of electrode-potential between Zn and Al, so La and Y elements can restrain the inter-granular corrosion and enhance the corrosion resistance of ZA alloys.The stress distribution along interfaces between the matrix and the refilled particle in SiC_p/ZA27 composite under loading was calculated by using finite element method, and the plastic strain in the matrix was also investigated. The heat residual stress distribution was analyzed with elastic and plastic finite element model. Results show that: normal stress along interface makes interfacial de-bonding under tensile loads; von Mises stress makes matrix yield at the interface between pole area and equator area; refilled particles prone to fracture brittlely as it is under triaxial tensile in residual stress field. Because the residual normal stress at interface is greater, it is possible to make the interface de-bonding. The tangential residual stress in the matrix near interface can restrain the crack to extend. When the composite is overload, the heavy plastic strain occurs in the matrix, which gives rise to a lot of crisscross cracks under high temperature and high pressure, which makes the interface between the matrix and the refilled particle de-bonding. The bigger the relative size of particle, the smaller theplastic strain in matrix. That is to say the refilled particle can enhance the plastic strain resistance of the composites.The complex optimization without formula was carried out by the combination of artificial neural net work with simulated annealing calculation. A new model of multi-target optimization was put forward, which soh’ed the problem of improving multiple mechanical properties of alloys at the same time. Mechanical properties of alloys were predicted and the casting technique parameter was optimized with this method.更多还原