The microstructures and corrosion behavior of AlSi5Cu1Mg alloy modified with different contents of La were investigated. Optical microscopy observations showed that the microstructures of AlSi5Cu1Mg-xLa (x = 0, 0.3, 0.6, and 0.9 wt%) alloy transformed from coarse cellular to fine cellular as the content of La increased from 0 to 0.9 wt%. The results of electrochemical measurement and immersion test in 3.5 wt% NaCl solution showed that the corrosion resistance of AlSi5Cu1Mg-xLa alloy strongly depended on its microstructures. The AlSi5Cu1Mg-0.6La sample exhibited the highest corrosion resistance due to its fine cellular structure and the cathode phases coated by the La element. The covering film of La hindered the corrosion electron flowing between the cathode and the anode. As a result, the corrosion current density of the AlSi5Cu1Mg-0.6La alloy was only about 40% that of the matrix alloy in the electrochemical measurement.

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We investigate theoretically the THz optical bistability properties of graphene-based heterostructures. We derive a simple procedure to calculate the nonlinear transmission in graphene-based heterostructures. It is found that the hysteretic response occurs when the frequency of the incident light is less than critical frequency. Compared with the traditional nonlinear materials, THz optical bistability can be tuned more effectively in the proposed structure. It is shown that the optical bistability can be electrically controlled via suitably varying the applied voltage on the graphene, and can also be tuned by adjusting incident angle, the frequency of the incident light, and the refractive index of the constituent materials. The bistable thresholds can be lowered markedly by decreasing the Fermi energy or incident angle.

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