【作者】 刘放军；

【导师】 陈振华；

【作者基本信息】 湖南大学 ， 材料加工工程， 2006， 硕士

【摘要】 压铸是最常用的汽车零件成型方法,具有生产效率高、产品表面质量好等优点。ZA84镁合金是Mg-Al-Zn三元合金中性能较好的成分组合,其高温力学性能优于常用的AZ91合金,有望用于使用温度高于120℃的汽车零部件上。然而,目前有关ZA84合金压铸工艺和性能方面的研究很少。因此,开展ZA84镁合金压铸工艺和性能的研究具有很大的实际应用价值。本论文采用冷室压铸机,开展了ZA84镁合金压铸工艺的研究,考察了压射速度、压射比压、浇注温度和模具温度对铸件的表面质量、力学性能和微观组织的影响。在此基础上,考察了Sn含量(0~1.5mass%)对ZA84合金相组成、显微组织、力学性能和热稳定性的影响。实验得到了如下结果:①与慢压射相比,在其他工艺参数相同的情况下,快压射条件下合金可获得更好的力学性能;随着压射比压的增加,ZA84压铸件密度增加,显微组织细化,从而力学性能得到提高;随着浇注温度的升高,ZA84合金压铸件密度出现降低的趋势,其力学性能的变化趋势是先升高而后降低;在模具温度为120℃,ZA84合金压铸件密度最大,随着模具温度升高,其抗拉强度与硬度都有所增加,延伸率先增加而后略有降低。②ZA84合金优化工艺参数依次为:压射速度为快压射,压射比压为60MPa,浇注温度为690±10℃,模具温度为170±10℃。③ZA84合金由α-Mg、Mg32(Al,Zn)49和MgZn三相组成,加Sn后ZA84合金由α-Mg、Mg32(Al,Zn)49、MgZn和Mg2Sn四相组成,Sn的加入有抑制MgZn生成和促进Mg32(Al,Zn)49相析出的作用。④Sn合金化ZA84合金中存在细小Mg2Sn颗粒相,在晶界和晶内分布,且随着Sn含量增加,Mg2Sn相数量增多,尺寸变大。⑤Sn合金化ZA84合金的强度随着Sn含量的增加呈现先增加后降低的趋势,在Sn含量为1mass%时ZA84合金力学性能最好。⑥ZA84+1.0Sn合金退火后的组织无明显变化,其退火后硬度略有下降,但与ZA84合金退火后硬度下降相比,其变化不那么明显,故加Sn后ZA84合金的热稳定性得到提高。更多还原

【Abstract】 Die casting, characteristics of high production efficiency, good product quality and etc. is the most widely used method for the fabrication of components in automobiles. ZA84 magnesium alloy is a better composition of good mechanical properties among the Mg-Al-Zn ternary system, with its high-temperature mechanical properties superior to conventional AZ91 alloy, and it is desirable to find applications in the components of automobiles with the service temperature higher than 120℃. However, there has been few studies on die casting process and mechanical properties of ZA84 magnesium alloy up to now. Therefore, it is of great signifance to develop the optimized die casting process of ZA84 alloy and investigate the effects of alloying on its mechanical properties.the die casting process of ZA84 alloy was developed on a cold chamber die casting machine . The effects of injection velocity, injection pressure, pouring temperature and mold temperature on the surface quality, microstructure and mechanical properties of ZA84 die casting were investigated. According to the optimized die casting process, the effects of the content of Sn on the phase constitutions, microstructure, mechanical properties and thermal stability of ZA84 alloy were studied. The experimental results demonstrated that:①Die castings with fast injection possessed superior mechanical properties to those of slow injection with the other technical parameters unvaried. Die castings had finer microstructures and higher density with the injection pressure increasing, and thus the strength was greatly improved. As the pouring temperature increased, the density of die castings decreased, and the mechanical properties increased firstly then decreased. At the 120℃of the mold temperature, the density of ZA84 die casting increased, with the mold temperature increasing, tensile strength and hardness increased, but elongation increased firstly and then decreased.②Fast injection, injection pressure of 60MPa, pouring temperature of 690±10℃, and mold temperature of 170±10℃were the optimized die casting process parameters for the ZA84 magnesium alloy.③ZA84 alloy was composed ofα-Mg, Mg32(Al,Zn)49 and MgZn , while the alloy containing Sn was composed of four phases i.e.α-Mg, Mg32(Al,Zn)49, MgZn and Mg2Sn.④The addition of Sn played a role in prohibiting the formation of MgZn and accelerating the precipitation of Mg32(Al,Zn)49. The fine, dispersed Mg2Sn particles were distributed both at the grain boundary and in the grain, the amount of which更多还原