The Modified Of Al-Si In Situ Composites
Edward Guzik, Dariusz Kopyciński Akademia Górniczo-Hutnicza w Krakowie, Wydział Odlewnictwa, ul. Reymonta 23, 30-059 Kraków
Annals 1 No. 1, 2001 pages 72-75
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abstract The paper presents results of the research on unidirectional crystallization of modified α(Al)-Si alloys. Relation between interfibre spacing λ and growth rate v has been established by the use the Bridgman type device for unidirectional crystallization. In order to achieve the assumed aim a specialized device for unidirectional crystallization of Bridgman type with vertical temperature gradient has been assembled. The method is based, roughly speaking, on melting of entire volume of metal in a form and subsequently on continuous pulling the form out of the furnace into the cooling medium. The device for unidirectional crystallization consists of electrical resistance furnace, cooler and drive mechanism. In addition it is equipped with the freezer of samples and the microprocessor that stabilizes the high temperature with accuracy up to 2ºC and assures required speed range of crucible with liquid metal movement in the furnace. During the unidirectional crystallization the speed of the sample translation was in the range of v = 1.11 • 10–4÷1.81 • 10–3 cm/s, what was - in first approximation - equivalent to the eutectic growth rate. Strontium that is added to α(Al)-Si alloy effects: 1. Transition from lamellar to fibre eutectic - Fig. 4. 2. The eutectic silicon fibre grows according to mechanism shown at Fig. 1a. 3. It has been observed that the increase on growth rate v results in the decrease of value of parameter λ (relationship (1)). 4. Clear increase of the average undercooling ΔT according to the relationship (2).