Technological aspects of synthesis of ALFA composites
Jerzy Sobczak*, Paweł Derłak**, Andrzej Wojciechowski***, Krystyna Pietrzak***, Dariusz Rudnik*** *Instytut Odlewnictwa, ul. Zakopiańska 73, 30-418 Kraków Instytut Transportu Samochodowego, ul. Jagiellońska 80, 03-301 Warszawa **Instytut Odlewnictwa, ul. Zakopiańska 73, 30-418 Kraków ***Instytut Transportu Samochodowego, ul. Jagiellońska 80, 03-301 Warszawa
Quarterly No. 3, 2005 pages 3-10
DOI:
keywords:
abstract Aluminum-fly ash (ALFA - ALuminium Fly Ash) composites have been developed in recent years. Fly ash is a particulate waste material formed as a result of coal combustion in power plants. The use of fly ash as a filler or reinforcement for aluminum alloys called Metal Matrix Composites, or MMCs, is therefore very desirable from an environmental standpoint. Fly ash forms at temperatures in the range of 920÷1200ºC and is collected as precipitator ash (solid particles) and cenospheres (hollow microspheres) that float on collection ponds. Production of aluminum alloy-fly ash composite material is difficult due to the poor wettability of fly ash and its light weight nature. The introduction of fly ash into liquid metal for making gravity castings oftentimes does not result in a uniform distribution of fly ash particles in the alloy structure. However, further re-melting of the composite material combined with squeeze casting has been found to improve the distribution in aluminum-fly ash castings. Initial investigations employing a squeeze casting process (the application of external pressure on the molten metal) for Aluminumfly ash MMCs has also demonstrated many advantages for this technique, i.e.: better compatibility between the metal matrix and the fly ash particles, a more improved structure of the matrix alloy, filling of some hollow particles of the fly ash with metal, and pressure activation of the fly ash-metal interface. In this work authors described some technological aspects of ALFA synthesis. The results have been considered basing on the long term collaboration between Foundry Research Institute, Motor Transport Institute and Energy of Industry Co. from Ohio, USA. Selected methods allow producing the material, which can be applied as the construction material. In a first method, powder metallurgy, fly ash was tentatively prepared (Fig. 2) and then was melted with aluminum matrix. The mechanical properties and structure were shown in Figure 3 and Table 2. The second method, pressure infiltration, needs to prepare a ceramic perform (Fig. 5), which next is infiltrated by liquid metal (Fig. 6). Obtained structures were shown in Figure 7. The third method, using liquid phase, allows producing composite with homogeneous distribution, but it still reveals unfavorable phenomena - floatation of light fly ash particles. Obtained structure was shown in Figure 10. During described research, a high energy acoustic emission was noticed, called by authors the SODA effect (available on Internet: http://darlak.neostrada.pl/soda). Key words: fly ash, technology, metal matrix composites, SODA effect