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Graphene-reinforced 7055 aluminum alloy composites with different contents of graphene were prepared by spark plasma sintering（SPS）. The structure and mechanical properties of the composites were investigated. Testing results show that the hardness, compressive strength, and yield strength of the composites are improved with the addition of 1wt% graphene. A clean, strong interface is formed between the metal matrix and graphene via metallurgical bonding on atomic scale. Harmful aluminum carbide（Al_4C_3） is not formed during SPS processing. Further addition of graphene（above 1wt%） results in the deterioration in mechanical properties of the composites. The agglomeration of graphene plates is exacerbated with increasing graphene content, which is the main reason for this deterioration.

Aluminum becomes the most popular nonferrous metal and is widely used in many fields such as packaging,building transportation and electrical materials due to its rich resource, light weight, good mechanical properties, suitable corrosion resistance and excellent electrical conductivity. Grain refinement, which is obtained by changing the size of grain structure by different techniques, is a preferred method to improve simultaneously the strength and plasticity of metallic materials. Therefore, grain refining of aluminum is regarded as a key technique in aluminum processing industry.Up to now, there have been a number of techniques for aluminum grain refining. All the techniques can be classified as four categories as follows： grain refining by vibration and stirring during solidification, rapid solidification, the addition of grain refiner and severe plastic deformation. Each of them has its own merits and demerits as well as applicable conditions, and there are still some arguments in the understanding of the mechanisms of these techniques. In this article, the research progresses and challenges encountered in the present techniques and the future research issues and directions are summarized.

Stir casting is an economical process for the fabrication of aluminum matrix composites. There are many parameters in this process, which affect the final microstructure and mechanical properties of the compos- ites. In this study, micron-sized SiC particles were used as reinforcement to fabricate A1-3 wt% SiC composites at two casting temperatures （680 and 850 ℃） and stirring periods （2 and 6 min）. Factors of reaction at matrix/ceramic interface, porosity, ceramic incorporation, and agglomera- tion of the particles were evaluated by scanning electron microscope （SEM） and high-resolution transition electron microscope （HRTEM） studies. From microstructural char- acterizations, it is concluded that the shorter stirring period is required for ceramic incorporation to achieve metal/ce- ramic bonding at the interface. The higher stirring tem- perature （850 ℃） also leads to improved ceramic incorporation. In some cases, shrinkage porosity and intensive formation of A14C3 at the metal/ceramic interface are also observed. Finally, the mechanical properties of the composites were evaluated, and their relation with the corresponding microstructure and processing parameters of the composites was discussed.

In this study, 6061 aluminum alloy and AZ31 B magnesium alloy composite plate was fabricated through explosive welding. Molecular dynamics（MD） simulations were conducted to investigate atomic diffusion behavior at bonding interface in the AI/Mg composite plate. Corresponding experiments were conducted to validate the simulation results. The results show that diffusion coefficient of Mg atom is larger than that of A1 atom and the difference between these two coefficients becomes smaller with increasing collision velocity. The diffusion coefficient was found to depend on collision velocity and angle. It increases linearly with collision velocity when the collision angle is maintained constant at 10° and decreases linearly with collision angle when the collision velocity is maintained constantly at 440 m/s. Based on our MD simulation results and Fick＇s second law, a mathematical formula to calculate the thickness of diffusion layer was proposed and its validity was verified by relevant experiments. Transmission electron microscopy and energy-dispersive system were also used to investigate the atomic diffusion behavior at the bonding interface in the explosively welded 6061/AZ31B composite plate. The results show that there were obvious Al and Mg atom diffusion at the bonding interface,and the diffusion of magnesium atoms from magnesium alloy plate to aluminum alloy plate occurs much faster than the diffusion of aluminum atoms to the magnesium alloy plate. These findings from the current study can help to optimize the explosive welding process.

The nanostructured γ and α alumina powders were synthesized by sol-gel and co-precipitation methods, and properties of the powders were studied by XRD, SEM, TEM, BET and FTIR. The results showed that both γ and α phases were formed in the lower temperature in precipitation method compared to sol-gel. The size of spherical α -alumina synthesized by sol-gel was 10–15 nm, whereas the sample prepared by co-precipitation yielded nearly spherical and hexagon α -powder with particle size of 10–50 nm. At 750 °C the resulting powder prepared by co-precipitation exhibited larger surface area (206.2 m 2 /g) compared to sol-gel (30.72 m 2 /g), hence it is recommended for catalytic and sensing applications.

The Nanling metallogenic belt in South China is characterized by well-developed tungsten-tin mineralization related to multi- ple-aged granitoids. This belt is one of the 5 key prospecting and exploration areas among the 19 important metallogenic tar- gets in China. Important progress has been made in recent years in understanding the Nanling granitoids and associated miner- alization, and this paper introduces the latest major findings as follows： （1） there exists a series of Caledonian, Indosinian, and Yanshanian W-Sn-bearing granites; （2） the Sn-bearing Yanshanian granites in the Nanling Range form an NE-SW trending aluminous A-type granite belt that stretches over 350 km. The granites typically belong to the magnetite series, and dioritic micro-granular enclaves with mingling features are very common; （3） the Early Yanshanian Sn- and W-bearing granites pos- sess different petrological and geochemical features to each other： most Sn-bearing granites are metaluminous to weakly per- aluminous biotite （hornblende） granites, with zircon tHe（t） values of ca. -2 to -8, whereas most W-bearing granites are peralu- minous two-mica granites or muscovite granites with CHf（t） values of ca. -8 to -12; （4） based on the petrology and geochemis- try of the W-Sn-bearing granites, mineralogical studies have shown that common minerals such as titanite, magnetite, and bio- tite may be used as indicators for discriminating the mineralizing potential of the Sn-bearing granites. Similarly, W-bearing minerals such as wolframite may indicate the mineralizing potential of the W-bearing granites. Future studies should be fo- cused on examining the internal relationships between the multiple-aged granites in composite bodies, the metallogenic pecu- liarities of multiple-aged W-Sn-bearing granites, the links between melt evolution and highly evolved ore-bearing felsic dykes, and the connections between granite domes and mineralization.

Bauxite in China remains an urgently needed resource largely dependent on imports. Based on the study of the newly- discovered Dazhuyuan bauxite deposit in northeastern Guizhou, we have found new enrichment of tungsten and lithium in bauxite, with the highest WO3 content up to 0.33% and the highest Li20 content up to 0.58%. The present paper reports the in- itial result, and the spatial distribution feature of W and Li in the ore body （with Li enriched mostly in the north part of the west limb of the Liyuan syncline, whereas W enriched mostly in the central part of the east limb）. The results suggest that it is necessary to delineate lithium and tungsten ore body independently, discuss the feasibility of its industrial utilization, and point out the new direction of synthetic appraisal for such kinds of traditional mineral resources, in order to forecast and assess bauxite resources in the region.

The microstructure and mechanical properties of 6061 aluminum alloy were studied by using the aging treatment of 540 ℃/3 h solid solution+60% reduction axial closed die rolling+180 ℃/1.5-8 h. Comparison was made with the aging treatment of 60% reduction rolling+540 ℃/3 h solid solution+180 ℃/8 h. The results show that after axial closed die rolling thermo-mechanical treatment, the dislocation density of the aluminum alloy increases, the PFZ width decreases, and the spheroidized β″ phase appears. The aluminum alloy obtains good comprehensive mechanical properties at the aging time of 2.5 h, the yield strength of 333 MPa and the tensile strength of 359 MPa. As the aging time gets longer, little change took place in the grain size of the aluminum alloy, the granular Mg 2 Si precipitates in the grain decrease, and a small amount of coarse granular Mg 2 Si precipitates appear at the grain boundary. The dimple at the tensile fracture gradually changes from large and deep to small and shallow, and the ductility of the aluminum alloy decreases with the aging time. 以540 ℃/3 h固溶+60%压下量轴向辗压+180 ℃/1.5~8 h时效的6061铝合金为研究对象, 通过与60%压下量镦粗+540 ℃/3h固溶+180 ℃/8 h时效处理对比, 研究了合金的组织和力学性能。结果表明: 进行轴向辗压形变热处理后, 合金内的位错密度增大, 无沉淀析出带(PFZ)宽度有所减小, 出现球化β″相; 合金在时效时间2.5 h时获得较好的综合力学性能, 屈服强度为333 MPa, 抗拉强度为359 MPa。随着时效时间延长, 合金的晶粒尺寸变化不大, 晶粒内部的颗粒状Mg 2 Si析出相有所减少, 晶界上出现少量粗大的颗粒状Mg 2 Si析出相; 拉伸断口处韧窝由大而深逐渐转变为小且浅, 合金的塑性随着时效时间的增加呈下降趋势。

Over the last five years, accumulative roll bonding （ARB） has been used to produce aluminum-based metal matrix composites （AMMCs） with ultrafine-grained （UFG） structure. Al/Al2O3 [1-3], Al/SiC [4], Al/B4C [5,6], and Al/WC [7] are currently fabricated using ARB because of the resulting highly uniform reinforced particle distribution. ARB composites have higher strength but poorer ductility than unreinforced UFG matrix because stress is concentrated in the reinforced phase-Al matrix interface during tensile process. In the present study, we introduced Al-Zn regions to AI matrix by ARB to obtain AMMCs with high strength and ductility. The dissolution and precipitation of Zn atoms in Al matrix, as well as the effects of Zn on the ductility of AMMCs, were also analyzed.

The objective of this research is to improve the thermal conductivity and mechanical properties of Al/GNPs（graphene nanoplatelets） nanocomposites produced by classical powder metallurgy and hot rolling techniques. The microstructural evaluation confirmed the uniform dispersion of GNPs at low content and agglomeration at higher contents of GNPs. The structure of graphene was studied before and after the mixing and the Raman spectrum proofs that the wet mixing has a great potential to be used as a dispersion method. There was no significant peak corresponding to the Al_4C_3 formation in both the differential scanning calorimetry curves and X-ray diffraction patterns. The microstructural observation in both fabrication techniques showed grain refinement as a function of the GNPs content. Moreover, the introduction of the GNPs not only improved the Vickers hardness of the composites but also decreased their density. The thermal conductivity investigations showed that in both the press-sintered and hot-rolled samples, although the thermal conductivity of composites was improved at low GNPs contents, it was negatively affected at high GNPs contents.