ISSN:
1662-9779
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Physics
Notes:
Semi-solid casting (SSC) techniques have proven useful in the mass production of high integritycastings for the automotive and other industries. Recent research has shown metal matrixnanocomposite (MMNC) materials to have greatly improved properties in comparison to their basemetals. However, current methods of MMNC production are costly and time consuming. Thusdevelopment of a process that combines the integrity and cost effectiveness of semi-solid castingwith the property improvement of MMNCs would have the potential to greatly improve cast partquality available to engineers in a wide variety of industries. This paper presents a method ofcombining SSC with MMNC in a way that benefits from MMNCs’ tendency to naturally form theglobular microstructure necessary for SSC. This method uses ultrasonically dispersed nanoparticlesas nucleating agents to achieve globular primary grains such that fluidity is maintained even at highsolid fractions. Once particle dispersion is achieved, the material needs no further processing tobecome a semi-solid slurry of globular primary grains as it cools. This quiescent method of slurryproduction, while still imposing some constraints on cooling rates, has a large process windowmaking this process capable of industrial rates of throughput. It was found that the key factor toachieving globular microstructure is a sufficiently slow cooling rate at the onset of solidificationsuch that particle-induced nucleation can occur. Once nucleation occurs, continued cooling isvirtually unconstrained, with globular microstructure evident in quenched samples as well assamples cooled at rates as slow as 1 °C/min. This method was demonstrated in several materialsystems using zinc (Zn), aluminum (Al), and magnesium (Mg) alloys and nanoparticles ofaluminum oxide (Al2O3), silicon carbide (SiC), and titanium oxide (TiO2). Additionally, severalnucleation models are examined for applicability to nanoscale composites
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/22/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.116-117.478.pdf
