The effect of one-step aging temper on the mechanical properties, electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated. The results indicated that with elevating the aging temperature from 100℃ to 160℃, the aging response rate was greatly accelerated, and the UTS at peak aging condition decreased, while the corresponding TYS increased. However, the electrical conductivity of the alloy became higher. After aging for 24 h at 120℃, the peak UTS and TYS values were achieved as 591 MPa and 541 MPa, respectively; but the alloy achieved a lower conductivity, 20.4 MS/m. When T6 temper was performed at 140℃ for 14 h, the UTS decreased only by 1% of the former, whereas the TYS and the electrical conductivity increased obviously, which were up to 559 MPa and 22.6 MS/m, respectively. The major strengthening precipitates of the peak-aged alloy were GP zones and η′ phase. The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature. There were obvious PFZs along the grain boundary both in T6 conditions aged at 140℃ and 160℃.Al-Zn-Mg-Cu alloy, one-step aging, properties, microstructure

To study the energy evolution law and damage constitutive behavior of high-strength concrete based on the conventional triaxial compression tests of C60 and C70 high-strength concrete subjected to five different confining pressures, the failure characteristics of high-strength concrete are analyzed at different confining pressures, and the evolution of the input energy density, elastic strain energy density, and dissipation energy density with axial strain and confining pressure are quantified. Combined with a continuous damage theory and non-equilibrium statistical method, the ratio of dissipation energy density of concrete to dissipation energy density corresponding to peak stress is used as the mechanical parameter. Assuming that the mechanical parameter obeys the Weibull distribution laws, the statistical damage variable describing the damage characteristics of concrete were derived. According to the Lemaitre strain equivalent principle, the damage variable is introduced to the generalized Hooke law to establish the statistical damage constitutive model for high-strength concrete. The results show that: (1) the input energy density and dissipation energy density increases with the increase of axial strain, while the elastic strain energy density increases first and then decreases as a function of the axial strain and reaches the maximum value at the peak stress; (2) the input, elastic strain, and dissipated energy densities corresponding to the peak stress of the two high-strength concretes all increase as a function of confining pressure, and the elastic strain energy density corresponding to the peak stress increases linearly as a function of the confining pressure; (3) the statistical damage constitutive model results of C60 and C70 high-strength concrete are in good agreement with the test results, and the average relative standard deviations are only 3.64% and 3.99%. These outcomes verify the rationality and accuracy of the model.

This research aims at a further exploration of surface treatments of carbon fibers to improve the performance of CFRC. Two approaches to treat carbon fibers were used in this study. SEM, IR, XRD were used to analyse the CFRC prepared with treated carbon fibers. Because of strong adhesion, CFRC prepared using CF with treatment has a better performance than that without treatment. Flexural strength is 30% higher, tensile strength is 48% higher, impact strength 63% higher, and deflection is increased.

Different volume ratios of Al2O3 powder and copper powder are mixed, and a copper-based composite coating is prepared on a pure copper matrix by low-pressure cold spraying technology.The hardness and bond strength of the coating were tested, and the cross-section of the coating was observed and analyzed with a field emission scanning electron microscope. The effect of Al2O3 content in the original powder on the coating performance was investigated.The experimental results show that the copper-based composite coating prepared from copper powder with a particle size range of 10-40μm has a lower porosity and a denser coating structure.With the increase of the content of Al2O3 in the original powder, both the microhardness and the bond strength of the coating showed a law of increasing first and then decreasing. When the content of Al2O3 was 20%, the coating had the best performance.