The Study Of Heat Treatment Theory On Hyper-Eutectic Al-Si Alloy

The casting hypereutectic Al-Si alloy has the advantages of low density, high strength, high weldability, good castability,good abrasion resistance and heat resistance. Because it has the characteristics of thermal expansion coefficient and high thermal stability, it is the most studied and applied as piston material. As the piston works in the high-temperature long-term working environment, so there has strict requirements about high temperature strength of the piston. By means of improving the heat treatment conditions, to increase overall performance of the hypereutectic Al-Si alloy and lengthen their service life. This is huge significant to expand the application scope of the Al-Si alloy. These experiments are about observing the morphology of the alloy which in the presence of TEM, SEM,X-ray, etc.and casting by conventional method. It analyzed the strengthening mechanism of the alloy heat treatment strengthening and precipitation characteristics of strengthening phase.The results show that the cast hypereutectic Al-Si alloy after 520℃*10h solution treatment and single ageing treatment in 175℃, the alloy hardness gradually increase with the time of aging treatment, after 8h and 14h aging treatment, each of them reach the peak hardness, hardness curves appeared double peaks, meanwhile the two tensile strengths in room temperature and high temperature were both increased. After 100℃*4h pre-aging treatment,175℃final aging treatment in 2h and 10h, the hardness curves also appeared double peaks. Final aging in 10h, the two tensile strengths in room temperature and high temperature reached maximum. RRA(regression re-aging) could also increase the alloy hardness, but it has little effect on tensile strength in both room and high temperature. Comparing the three aging processes, it is found that the mechanical properties of alloy reached the best after 100℃*4h pre-aging treatment,175℃final treatment in 1 Oh,After aging 175℃single ageing treatment, we found precipitated the G.P zone and metastable phase in the TEM photo. There precipitation is the direct cause of increasing mechanical properties. After 24h aging treatment,the stable phase has formatted, it destroyed the coherent relationships with the matrix and caused mechanical properties descend.