Age-Hardening Effect Of Cast AlSi Alloys

Universal material testing machine, thermal analyzer, optical microscope, scanning electronic microscope (SEM) and energy disperse spectroscopy (EDS) and many kinds of other testing technology were used to research the age-hardening effect of cast Al-Si alloy series. The contribution of micro-alloying of Mg, Sb, Mn, Ti, Zr, Zn, Sn, Cu to Al-Si alloy microstructure, properties and aging behavior this paper studied through the judging experiment. On the base, the age-hardening behavior and aging precipitation behavior of Al-7Si-0.55Mg alloy were studied. The influence of Ti element on the aging behavior of ZL114 alloy was studied. The influence of Mg content on the aging behavior of ZL114 alloy was investigated using DSC analysis, age-hardening curves and metallographic analysis. The effect of age-hardening on ZL114 alloy was investigated in different solidification rates and different heat treatment conditions. Main research findings are as follows:(1) Micro-alloying of Mg, Sb, Mn, Ti, Zr, Zn, Sn and Cu influences microscopic structure and mechanical property of Al-7Si alloy greatly. Adding Ti, Zr and Cu, Al-7Si alloy can obviously refineα- Al grain, and raise the Vickers-hardness, and represent age-hardening characteristic; 1% Mn makes no effect to ageing strengthening of Al-7Si alloy; Sb can modify morphology of the eutectic silicon; dendritic columnar crystals are observed after adding Zn and Sn; after adding Mg, Al-7Si alloy shows notableage-hardening effect, and the SSS→βconversion enthalpy measured by DSCanalyser is 3.776J/g.(2) Al-7Si-0.55Mg alloy shows obvious age-hardening characteristics. The precipitation process: supersaturated solid solution—Mg/Si atom aggregation zone—equilibrium phase. Adding Ti to AlSiMg alloys, Al₃Ti phase can be founded and the peak value of aging hardness is in advance and the hardness in overaging process falls comparatively slowly.(3) For the first time DSC of Al-7Si-0.55Mg alloy was measured in 175℃isothermal process. The exothermic reaction occurs at 160²10min, and the latent heat of this transition is 3.296J/g. Comparing with the latent heat of SSS→β, a conclusion can be drawn that the hardening phase of 175°C aging is a metastable phase, notβphase.(4) When adding more Mg to ZL114 alloy, the latent heat of phase change increases at the same time, and the time to reach peak value is bigger. When adding more Mg to ZL114 alloy, the density of strengthening phase is higher and the hardness peak value is higher in age-hardening process.(5) ZL114 alloy shows great sectional sensitivity in the foundry process. When the casting section thickness is thinner, ZL114 alloy grain is refiner and dendrite arm spacing (DAS) is smaller. The faster solidifying rate is, the higher hardness of cast is. But, the solidifying rate makes little contribution to age-hardening behavior.(6) The higher solution treatment temperature is, the better age-hardening effect ZL114 alloy has. It shows that ZL114 alloy alloy has great quenching sensitivity. The effect of age-hardening is obvious at 175°C aging. There is no abvious age-hardening phenomenon at 300℃aging progress.