ISSN:
1662-9779
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Physics
Notes:
The effect of reheating to the semisolid state (soaking treatment) on the microstructureevolution of the A356 aluminum alloy prepared by ultrasonic melt treatment was studied in thispaper. The results showed that in general the longer the soaking process the larger and the moreround the grains obtained. Higher roundness occurs at shorter soaking times in the fine-grained ascastsamples, and at longer times in the inhomogeneous or the coarser-grained as-cast structures.The optimum thixotropic condition (high roundness, 0.72, and small globule sizes 〈 90 μm) areachieved after 5 min. soaking in the samples treated by UST at 623 and 620oC, which is the typicalsoaking time dictated by the industrial practice in SSM. The amount of entrapped eutectic asobserved after soaking treatments is uniquely very small, suggesting that the UST-treated ingots willhave better formability in the semisolid state. The growth rate constants are substantially low: in theorder of 479-748 μm3/s. These growth rate constants are much lower than those reported for MHDcastA356 ingots. The growth rates of the samples produced by UST in the liquid state (i.e., 626,623 and 620oC. Note that liquidus temperature is 619oC) are lower than those of the samples treatedin the semi-solid temperatures, i.e., 617 and 614oC. The Ostwald ripening is most likely thedominant growth mechanism in the UST-treated samples during the soaking treatments. Theseresults reveal the feasibility and competence of UST as a potential route for thixotropic feedstockproduction
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/24/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.141-143.499.pdf
