Abstract
The influence of solution heat treatment parameters on T6 properties of unmodified and Sr-modified A356.2 alloys has been studied. The effects of solution temperature and time were investigated with ASTM B 108 test bars cast in sand molds and in permanent molds. Metallographic and image analysis techniques have been utilized to examine the microstructural changes occurring during heat treatment. The results indicate that the effect of Sr modification is to increase the spheroidization rate and lower the coarsening rate of Si particles. The solution temperature has a strong influence on Si particle morphology. Extremely high coarsening rates can be obtained at temperatures greater than 560° C. Solution treatment at these temperatures, however, has a detrimental effect on mechanical properties because of grain boundary melting. It has been established that solution times can be reduced significantly in modified samples. Increasing the solution temperature from 540 to 550°C enhances the strength properties.
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