Effects of Si Content on Microstructure and Mechanical Properties of 8079 Aluminum Alloy

Because of high strength and low breaking rate,8079 aluminum alloy has become the main material of double zero aluminum foil.However,there are still many problems in the manufacturing process,such as broken belt,pinhole and so on.As the main influencing element,Si has a great influence on the alloy.In this work,the influences of Si with various contents on microstructural evolution and mechanical properties of 8079 aluminum alloy were analyzed by energy dispersive spectrometer(EDS),optical microscope(OM),X-Ray diffraction analyzer(XRD),universal testing machine and Vickers hardness tester.The results showed that the primary Si phase was tiny and dispersed in the alloy when the content of Si is less than 1.3%.As the second phases dispersion strengthening,the Si phase can improve the strength of the alloy.However,when the Si content was too high,the Si phase increased and coarsened.Meanwhile,Fe-rich phase which increased by Si decreased the fine grain strengthening and the second phases strengthening mechanism.The coarse Si phase and the Fe-rich phase are brittle phase,which are easy to become the crack source in the process of material deformation and reduce the strength and toughness of the alloy.The mechanical property test shows that the performance of 8079 aluminum alloy is the best when the Si content is 1.3%.

Quantitative analysis of work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy based on true stress vs strain curves

The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for the onset of dynamic recrystallization （DRX） were determined based on the conventional strain hardening rate curves （dσ/dε versus σ）.The progress of DRX was analyzed by constructing a model of volume fraction of DRX based on flow curves.The strain rate sensitivity （SRS） and activation volume V were calculated.The results show that the DRX almost can happen under all deformation conditions even at high Z deformations where dynamic recovery （DRV） is the main softening mechanism.The DRX fraction curves can well predict the DRX behavior.The strain has significant effects on SRS at the strain rates of 0.01s-1 and 10s-1 which are mainly due to off-equilibrium saturation of dislocation storage and annihilation while the effects of the temperature on the SRS are based on the uniformity of microstructure distribution.The formation of ＂forest＂ of dislocation is contributed to the low activation volume V＊（about 168b3） which is independent of Z values at the initial deformation.The cross-slip due to dislocation piled up beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions at high strain （ε=0.6） while the fine DRX grains coarsed is the main reason for the high activation volume at low Z under the same strain conditions.

Microstructure and mechanical properties of tungsten composite reinforced by fibre network

In this paper the tungsten-fibre-net-reinforced tungsten composites were produced by spark plasma sintering （SPS） using fine W powders and commercial tungsten fibres. The relative density of the samples is above 95%. It was found that the recrystallization area in the fibres became bigger with increasing sintering temperature and pressure. The tungsten grains of fibres kept stable when sintered at 1350℃/16 kN while grown up when sintered at 1800℃/16 kN. The composite sintered at 1350℃/16 kN have a Vickers-hardness of -610 HV, about 2 times that of the 1800℃/16 kN sintered one. Tensile tests imply that the temperature at which the composites （1350℃/16 kN） begin to exhibit plastic deformation is about 200℃-250℃, which is 400℃ lower than that of SPSed pure W. The tensile fracture surfaces show that the increasing fracture ductility comes from pull-out, interface debonding and fracture of fibres.