Effect Of Sr Modification Research Articles

Effect of Al-5Ti-1B on the microstructure of near-eutectic Al-13.0%Si alloys modified with Sr

The addition of Sr in Al-Si alloys as a modifier causes a transition of the morphology of eutectic silicon from coarse plate-like or acicular to fine fibrous. However, it may also lead to the formation of long columnar dendritic α-Al phase. Al-5Ti-1B master alloy is often used as a grain refiner to achieve the fine equaixed grains in aluminum and aluminum alloys. The aim of the present study is to highlight the effect of Al-5Ti-1B master alloy additions on the microstructure of near-eutectic Al-Si alloys modified with Sr. When the addition of Al-5Ti-1B master alloy was below 0.82 mass%, the dendritic α-Al phase changed from long columnar to equiaxed, and there were no noticeable changes of the morphology and size of eutectic silicon, while the size of eutectic cells decreased slightly. However, when the addition was above 0.82 mass%, the deleterious influence of Al-5Ti-1B master alloy on the modification effect of Sr emerged and with further increases in addition level a fully unmodified microstructure was finally produced. The results indicate that the effective Sr in the melt decreases with increased addition of Al-5Ti-1B. The poisoning event of Al-5Ti-1B master alloy on the modification of Sr is supposed to be related with the interaction between Sr and Ti.

Effect of solution treatment parameters on tensile properties of cast aluminum alloys

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.