Impact On The Microstructure And Properties Of Alloys ZA4-1 Grain Refinement

As the requirements of people for life quality and health are increasing day after day, European and American countries strictly limit lead, cadmium, chromium element contents which include in traditional fashion jewelry materials. Developing a new material of green fashion jewelry is more urgent. Zinc alloy is the most accord with the requirement of jewelry production process, but the biggest problem is the casting hard brittle and easily broken. Thus, ZA4-1alloy is chosen as a base material, Ti,Ce and Al-5Ti-B are chosen as grain refiner for ZA4-1alloy, samples were prepared by the method of the silicone mold centrifugal casting, effects of Ti、Ce、Al-5Ti-B on microstructure and mechanical properties of ZA4-1alloy were studied by the universal testing machine, metallographic microscope, scanning electron microscopy (SEM) and X-ray diffraction. The results show that:Ti is a kind of effective grain refiner for ZA4-1alloy, the right amount of Ti content can refine the grain size. Ti will become as TiAl3in ZA4-1alloy, η(Zn) which first precipitation in ZA4-1alloy is nucleation and growth as TiAl3core,thus, main grains are refined. But when Ti content is too high, nucleation core will increase. Temperature gradient of front edge of the solid-liquid interface is reduced, latent heat which comes from core grew up can let grains dissolve and make the alloy grain boundary fuses in together. At the same time, solid solubility of Ti in η(Zn) is very low. Too much Ti which can’t solid to η(Zn) can enrichment at grain boundary, it can increase grain boundary defects and deteriorate the comprehensive mechanics performance of the ZA4-1alloy. In the silicone mold centrifugal casting ZA4-1alloy, the right Ti content is0.08%, the tensile strength of the alloy increase from250MPa to307MPa, and the elongation increase from1.2%to2.1%.Ce can neutralize the impurity elements and purify liquid in the ZA4-1alloy, improve comprehensive mechanical properties of the casting alloys. In the ZA4-1alloy, when the Ce content is0.1%, higher elongation will be gotten. But the content of Ce is unfavorable too high, when Ce content exceeds0.2%, a large number Ce dissolve out at the grain boundary, deteriorate the mechanics performance. At the same time, no matter how much the Ce to add in the castings, it can be seen many hole microstructures in casting alloy. When Ti and Ce are added to ZA4-1alloy, the alloy composition is ZA4-1-0.1Ce-0.12Ti. Th elongation of the alloy is2.5%, the tensile strength is285MPa, the elongation is improved greatly and the tensile strength is slightly reduced.In the silicone mold centrifugal casting ZA4-1alloy, Al-5Ti-B alloy has the best refinement effect. The right level of additive amount of Al-5Ti-B intermediate alloy is0.1%. The tensile strength is increased to170MPa, the elongation is increased to3%. Because Al-5Ti-B offers a large number of nunspontaneous nucleation TiAl3and TiB2for liquid alloy, TiAl3is face-centered cubic structure which has good compatibility with aluminum and is an important core of aluminum.TiB2can be used as heterogeneous nucleation core for η(Zn) and promoted η(Zn) grains nucleate and grow, to achieve the effect of refining grain size.Although grain refining can improve plastic toughness of ZA4-1alloy, properties of the alloy is difficult to meet by grain refining, the other method to improve plastic toughness of ZA4-1alloy will be researched by new alloy design and fabrication.