Hypoeutectic Al-si Alloy Primary Alpha Globular Crystal Rapid Formation Mechanism Are Discussed In This Paper

Semi-solid processing, as one of the21th century’s most promising net-shape forming technology, has long been concerning by people from the time when it was invented due to its many advantages. The preparation of eligible semi-solid slurry is the premise of semi-solid processing; therefore, it is of great significant to gain the semi-solid slurry with the primary phase which its crystalline grain has the small size and globular organization. Take all these into consideration, this paper use al-si alloy A356as the object, then try to find the law of primary a-Al evolution under the condition of isothermal heat preserved in solid-liquid area, in eutectic al-si alloy A356gained from the routine pouring process were experimentally investigated. At the same time, in order to gain the spheral semi-solid primary phase in the shorter time, this study use the method of grading isothermal heat preservation used in alloy A356.The results of the study show that:when treated in the way of630℃pouring and heat preservation at610℃by lmin～60mins time, the equal-area-circle diameter of the organization morphology of the semi-solid A356alloy primary phase presents the law of getting smaller firstly and getting bigger then, while the shape factor is presented to get better firstly and worse then with the extension of the time for heat preservation.In the condition of heat preservation for5mins totally, the morphology of the semi-solid primary phase got by the way of grading isothermal preservation at the temperature of610℃or578℃are much more better than that got by simple heat preservation at578℃and610℃temperature for5mins. The average equal-area-circle diameter of the A356alloy semi-solid primary phase presents the law of get smaller subtly and get bigger then and the shape factor also gradually improved with the extension of time at high temperature preservation when the alloy A356was treated in the condition of heat preservation at a low temperature (578℃) for0.5min and then a high temperature (610℃) for1min,2mins,3mins isothermal insulation and heat preservation. The roundness of the degree of alpha Al was getting more and more good, and the shape factor of the semi-solid primary phase of organization at high temperature heat preservation for3mins reaches0.76. Compared with the time spent previous, the time spent in the grading isothermal heat preservation is much shorter at the request of gaining the semi-solid primary phase with the same morphology.The distinguishing feature of this article is gaining the A356alloy semi-solid slurry with the nearly spherical morphology in the way of grading isothermal insulation treatment. To get the eligible roundness of the degree of the semi-solid A356primary phase, the grading isothermal heat preservation process could shorten its time in a certain extent.