Research On Canned Extrusion Process And Property Of Al-Based Amorphous Alloys

As one of the latest found amorphous alloys, aluminum-based amorphous alloys have attracted a great deal of attention in recent years due to their unique properties, including ultra-high strength, low density and high corrosion resistance. Because of limited glass-forming ability (GFA), only ribbons or powders can be prepared in the form of fully amorphous, which leads to the restriction of its industrial application. In order to acquire bulk amorphous material, consolidation method is put into use and it has been proved to produce the amorphous-nanocrystalline composite materials, not only keeping the original features, but also possessing some new performance. Based on that, investigation of the consolidation of aluminum-based amorphous alloys is of great significance and scientific value.The aim of this research is to comprehend the forming process of aluminum-based amorphous alloys and the properties of amorphous-nanocrystalline composite materials. On the basis of preparation methods and crystallization process known of amorphous alloys, powder extrusion is carried out to acquire bulk composite materials with optimized process parameters.This research is focused on preparation of amorphous Al86Ni6Y4.5Co2La1.5by gas atomization and the grain size distribution of powders. Based on that, warm extrusion is adopted to prepare bulk samples, of which the microstructure and mechanical properties are evaluated to establish the relationship between them. The main results are summarized as follow:(1) In Al-TM-RE systems, GFA of Al86Ni6Y4.5Co2La1.5relatively better than other Al-based amorphous alloys. Prepared by nitrogen gas atomization method, the powder could be sorted by diameter. The microstructure and thermal stability as a function of powder size were investigated. The content of amorphous phase is as high as100%in the<20μm size range and crystallizing degree is promoted with the increasing of powder size. The amorphous powder presents a glass transition temperature of238℃and a wide super-cooled liquid region of26℃. The thickness of Al2O3in the surface of amorphous powder is50nm.(2)6061A1adopted in warm extrusion as can material appears no defects. No chemical reaction or diffusion happens in the boundary between the two kinds of material, which is just mechanical bond.(3) Atomized amorphous Al86Ni6Y4.5Co2La1.s powders were successfully consolidated to bulky materials by warm extrusion. Crystallization phases are fcc-Al, Al3Y, Al9Co2and other unknown phases. As the extrusion temperature and ratio increase, crystallization degree and compact degree are promoted, nevertheless, the hardness of samples is declining.(4) Owing to the large amount of defects inside the samples, there is an evident gap between the actual breaking strength and the estimated. A lot of factors lead to the crack origin as well as the low breaking strength, for instance, holes in the compacts, oxide inclusion and so on.