Semi-solid Forming Eutectic Al-si Alloys And High Temperature Performance

Researching the hypereutectic Al-Si by semi-solid processing, people are craving in the forming craft which affects the microstructure, but whether the properties under this craft will be good or not is considered. As the ideal materials for the pistons, this paper researches the structures and properties of the high temperature by the semi-solid rheocasting and the sqeezing casting. The results of the paper will be the base on the successful applications of the pistons for the SSM of the hypereutectic Al-Si.The analyses for the ZL117 alloy by the semi-solid rheocasting and the squeeze casting, it shows that the average equivalent diameter of the primary silicon particles is the biggest on the bottom than the others, and the top is the bigger than the middle; the volume fraction of the primary silicon solid phase is the same rules; however, compared with the top, the volume fraction on the bottom exceeds 345%. Additionally, there are some casting flaws on the bottom, such as cavities, dispersal small holes, gathering big hole, etc. In order to overcome these flaws, some interrelated techniques need make better later.The mechanical properties experiments about the semi-solid ZL117 samples of the elevated temperature show that with the temperature increasing,δ₅ drops, and after 300℃it rises deeply, andδ₅ in 400℃is 18 times as long asδ₅ in 300℃,andσ_h drops ,in 400℃it is only 37.8MPa, and it is nearly the same to the ZL117σ_h by liquid squeezing casting, but it increases 9% than ZL109σ_h by metal casting. The hardness of HBS under the same annealing temperature of semi-solid ZL117 is almost equal to the ZL117σ_h by liquid squeezing casting, and it is higher than ZL109, even though it exceeds 10% in 36h.In the 150℃temperature wear experiments, the lose weight of the semi-solid squeeze casting ZL117 corresponds to the lose weight of liquid casting ZL117. Comparing with the lose weight of the ZL117 by the semi-solid rheocasting, the wear resistance of ZL109 is the worst because its lose weight is increases 57.2%.The study of thermal expansion coefficients about samples explains that the higher temperature, the higher coefficients. At the same temperature, the coefficient of ZL117 is only a little smaller by liquid squeezing casting than by semi-solid squeezing, but the coefficient of ZL109 by liquid metal casting is much bigger than them, and it adds 11% in 350℃.The results of high temperature oxidation of semi-solid forming hypereutectic Al-Si alloy manifests in the first phase oxidation increasing weigh is fast, and after a while the oxidation weigh is slowly, even stops in the end, as shows this alloy stands good anti-oxidation.This thesis replenishes especially the blank that belongs to the research in the fields of semi-solid forming hypereutectic Al-Si alloy. So it can offer support of theory and technology to go on studying and applying in the future.