时效Al-30Si微晶合金的组织演变及性能

Microstructure and performance of Al-30Si microcrystalline alloy during aging

利用单辊旋转甩带法制备快速凝固过共晶Al-30Si合金条带,对其进行不同温度下时效4 h和550℃下保温不同时间的时效处理,测定其硬度及耐磨性,采用扫描电镜(SEM)、透射电镜(TEM)及XRD技术对试验合金的微观组织进行表征,研究快速凝固合金时效处理后组织演变及性能。结果表明,快速凝固Al-30Si合金形成了微小初晶Si+纳米级颗粒状共晶硅弥散分布在α(Al)过饱和固溶体基体的复合组织;时效处理过程中,过饱和固溶的Si元素逐渐脱溶析出,以球状或依附于粒状共晶硅而析出生长;时效初期或时效温度较低时,初生硅发生缩颈、熔断、钝化,并逐渐粒化;随时效温度升高,硅相受扩散控制逐渐粗化长大,时效后期或时效温度达到550℃时,硅相逐渐以颗粒搭接和棱角小面特征长大,形态恶化。时效合金组织中硅相体积分数计算结果与定量金相测定结果基本一致。时效合金的显微硬度和耐磨性随时效温度的升高逐渐降低,室温润滑条件下的磨损机制主要为磨粒磨损。

A rapidly solidified hypereutectic Al-30 Si alloy ribbon was prepared by single roller melt-spinning method,the Al-30 Si alloy ribbon was aged at different temperatures for 4 h and at 550 ℃ for different time. The microhardness and wear resistance were tested and the microstructure were characterized by means of scanning electron microscopy( SEM),transmission electric microscopy( TEM) and XRD analysis. The results show that the microstructure of the rapidly solidified alloy is composed of primary Si and micro-nanostructure eutectic Si which are diffusely distributed in α supersaturated solid solution. During aging process, the silicon element in the supersaturated solidification can gradually precipitate from the matrix,and grow with sphere or attached to granular eutectic silicon.Primary silicon phase undergoes necking,stubbing,fragmentation,and transition to particles gradually in initial stage of aging or at low temperature aging. The growth of Si phase is a coarsening process controlled by diffusion as increasing aging temperatures. The morphology of Si phase deteriorates due to the occurrence of facets and lap in the final stage or at 550 ℃ aging. Calculations of Silicon phase volume fraction are accordance with the tested results of quantitative metallography. The microhardness and wear resistance of the aging alloy can gradually reduce as the increasing aging temperatures. The main wear mechanism of the alloy is abrasive wear.