Composition Design And Preparation Of Heat-Resisting Hyper-Eutectic Al-Si Alloy

Hyper-eutectic Al-Si alloys is good at casting and has high strength and other characteristic, so it is extensive used in automotive industy. In this thesis, the effect of addition of chromium and molybdenum has been studied.When 0.6wt. %Cr added in the complex dimensional hyper-eutectic Al-Si alloy, UTS of the alloy enhanced 6%. While after 0.6wt.% chromium and 0.4wt.% molybdenum added in the alloy simultaneously, UTS of the alloy enhanced 44.2%. The extensibility of the alloys fluctuate within a narrow range. SEM analysis showed that chromium and molybdenum can improve microstructure of the alloy and distribution of shapes. Chromium and molybdenum can form some chromium rich phases and some molybdenum rich phases. These changes can improve mechanical properties of the alloys.After T6 heat treated, the morphology of eutectic-Si have significant changes. Through analyzing the SEM photos of microstructure structure ,we find that the eutectic silicon has the remarkable changes at 525℃for 4h and 175℃for 10h.The passivating of silicon phase and the granulation of the second phases improve mechanical properties of the alloy. The T6 heat treatment can improve microstructure. these changes can improve mechanical properties of the alloy. The UTS of the heat treatmeat alloy reach 146.5MPa under high temperature. The plastic of the alloy get large improvement under high temperature.