Defect and Diffusion Forum Vol. 424

Abstract: In this study, the heat transfer coefficients of 7050 aluminum alloy under different water temperatures, polyalkylene glycol aqueous solution concentrations and quenching medium types are calculated by an iterative method, and the heat transfer coefficient of the aluminum alloy under different quenching medium parameters was compared and the difference was discussed in detail. The results show that with the increase of water temperature, the heat transfer coefficient of 7050 aluminum alloy gradually decreases; with the increase of polyalkylene glycol aqueous solution concentration, the heat transfer coefficient gradually decreases; the order of heat transfer capacity of quenching medium is disclosed among the studied medium types.

Abstract: In present work, a high Zn-containing Al-Zn-Mg-Cu alloy with different grain sizes was fabricated by extrusion and related precipitation characteristics and mechanical property were investigated after uniform heat treatments. The results showed that precipitation characteristics for the three alloys were almost the same. Matrix precipitates were GPII zone and η' phase and possessed small size and dense distribution while grain boundary precipitates exhibited discontinuous distribution. The rank of strength and fracture toughness for the three alloys are SG>MG>LG. Tearing ridges had been found on all the fracture surface while only LG alloy possess obvious dimple characteristics. The a-N curve showed that crack length list is MG>LG >SG under a same cycle number. The da/dN-ΔK curve also proved that fatigue crack propagation (FCP) rate of MG alloy is slightly larger than that of LG alloy, both were apparently larger than that of SG alloy. The width of fatigue striations on FCP fracture surface also backed it. Besides, obvious transgranular cracking characteristics and apparent secondary cracks were found on the FCP fracture surface.

Abstract: Fe and Si elements can form non-dissolvable phases in Al-Zn-Mg-Cu alloys and furtherly affect the property of finished products while the influence of minor contents lacks sufficient investigations. In present work, 7085 alloy with different Fe and Si contents (named by LFS alloy, MFS alloy and HFS alloy as Fe and Si contents progressively enhanced) was investigated and corresponding microstructure and property during the whole fabrication were analyzed via OM, SEM and DSC observation and tensile property, fracture toughness and salty-spray corrosion property. The results showed that Fe-containing phase existed in as-cast microstructure of three alloys while part of Fe-containing phases of HFS alloy has Si element. After homogenization treatment, coarse eutectic phases had dissolved into the matrix while Fe-containing phase remained in the alloys. Similarly, Si element existed in some Fe-containing phases of HFS alloy. The order of area fraction of remaining Fe-containing phases for the three alloys was LFS alloy<MFS alloy<HFS alloy. After extrusion, Mg(Zn,Cu,Al)₂ phase and Fe-containing phase possessed the majority, the former one was eliminated by solution treatment while the latter one had no obvious change. Under an unified aging treatment, the strength, elongation and fracture toughness were degraded with the increase of Fe and Si contents. Besides, the salt-spray corrosion property of HFS alloy was significantly inferior to LFS alloy and MFS alloy. This gave rise to a reference for controlling Fe and Si impurity of 7085 alloy for considering overall performance.

Abstract: The modification of high-performance lithium-sulfur battery cathode have been extensively studied. Suppressing the shuttle effect of polysulfide, solving the volume expansion of sulfur and the poor electrical conductivity of sulfur are the main directions for scientists to modify the cathode. Here we prepared bismuth ferrate powder doped with different molecular percentages of strontium by sol-gel method. Compared with the unmodified cell, the capacity and cycle stability were improved by adding as-prepared material to the cathode, which indicates that bismuth ferrate doped with certain amount of strontium plays a positive role in the cathode material modification.

Abstract: Ni-rich layered oxide cathode materials LiNi_xCo_yMn_zO₂ (x>0.6) have been widely used in high specific energy Li-ion batteries. Compared with polycrystalline LiNi_xCo_yMn_zO₂, single crystal Ni-rich cathode materials have attracted much attention for their unique advantages. However, they also suffer from some drawbacks, such rapid capacity decay and intragranular crack during cycling. In order to enhance the structure and electrochemical performance of single crystal LiNi_0.8Co_0.1Mn_0.1O₂ (SC811), different amount of aluminium (1 mol%, 2 mol% and 3 mol%) is utilized to substitute the materials. Physical characterizations of SC811 show the successful synthesis and Al doping of the single-crystal materials as well as lower Li/Ni intermixing after Al doping. Electrochemical tests illustrate that the single-crystal materials doped with 2mol% Al (2Al-SC811) shows superior electrochemical performance, and maintains 83.5 % of the initial discharge capacity after 100 cycles at 1 C in comparison with 68.9 % of the pristine SC811. It is hoped this work should shed light on the development of advanced cathode materials for Li-ion batteries.

Abstract: Aluminium source is one of the main factors affecting the physicochemical properties of SAPO-41.Silicoaluminophosphate molecular sieves-SAPO-41 were prepared via hydrothermal synthesis using di-n-butylamine (DBA) as templating agent, pseudo-boehmites, phosphoric acid and silica sol as aluminum, phosphorus and silicon sources respectively. Using XRD, N₂ physical adsorption, SEM and Py-IR analysis media, the effects of aluminum sources on the crystal and pore structure, morphology, B-acid center strength of the prepared SAPO-41 molecular sieves. The catalytic hydroisomerization performance over Pd/SAPO-41 bifunctional catalysts were investigated. Pseudo-boehmite type has little effect on the crystal structure and chemical composition of SAPO-41 molecular sieve, but has different effects on its morphology, pore structure, B-acid strength of SAPO-41, and Pd dispersion on Pd/SAPO-41. The hydroisomerization conversion of n-decane over 0.5Pd/S41-A1 can reach 88.56 %, and the selectivity of isoparaffin can reach 90.88%.This work provides a reference for selecting an ideal aluminum source for the synthesis of SAPO-41.