The Study Of Electronic Theory On The Microstructure Of ZA Alloys And The Interface Characteristics Of SiC_p/ZA27 Composites

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.