镁铝钆合金在空气中的氧化与燃烧

研究了在镁铝质量比为20:80的镁铝合金中加入稀土金属钆后,合金在空气中的氧化与燃烧特性。借助TG-DSC,SEM,XRD,EDS以及高速摄像仪等仪器对Mg-Al-Gd合金的氧化、燃烧过程及产物进行分析。结果表明:相对于不含钆的Mg-Al合金,Mg-Al-Gd合金在空气中的点火温度较低,约为487.6℃。在TG-DSC实验中,镁铝钆合金的氧化分为2个阶段,第1个阶段为镁的氧化反应,第2个阶段为氧化镁、铝以及氧气的反应,反应生成MgAl_2O_4。当Mg-Al-Gd合金在空气中燃烧时,合金粒子表面会形成一层薄的致密的氧化层,氧化层限制了合金粒子固相或液相的氧化,促进其气相燃烧,同时也导致燃烧出现喷射现象。燃烧没有生成MgAl_2O_4,而是形成了一种新的产物AlN。     

超声辅助对共沉淀法制备富锂锰基正极材料Li[Li_0.144Ni_0.136Co_0.136Mn_0.544]O₂性能影响的研究

通过超声辅助共沉淀法成功制备了富锂锰基正极电极材料,研究了不同的超声时间对材料形貌、结构和电化学性能的影响。研究发现,超声辅助能够使材料颗粒更加均匀,结构更合理,有利于材料电化学性能的提升。当合成前躯体材料超声时间为8h时,复合材料的放电比容量最好,在0.1C的初始放电比容量为327.8 mAh g_-1,均高于未超声的复合材料的265.2 mAh g_-1,1C下循环50圈后放电容量为181.6 mAh g_-1,保持率为84.8%。通过循环伏安法测试和电化学交流阻抗测试,发现超声后的复合材料还原氧化峰电流更大,电荷转移阻抗更小,具有较好的倍率性能。     

异种搅拌摩擦焊接AA2024-7075接头沿厚度方向上的电子背散射衍射分析

本研究以5mm厚的AA2024-T351和AA7075-T651铝合金板材进行搅拌摩擦对接焊,研究了异种铝合金搅拌摩擦焊AA2024-7075接头焊核区沿厚度方向的微观组织演化。研究结果表明：焊核区的晶粒尺寸从焊缝顶部到底部依次降低。轴肩区和焊缝底部区域的再结晶组分低于焊缝中心区。焊核区形成了简单的剪切织构且织构分布并不均匀。轴肩区主要是B 和?B织构组分,而底部区域主要是A 和?A织构组分,C织构组分则出现在中心区域。中心区域的织构强度低于焊核顶部和底部区域,这主要是由于该区域出现了洋葱环,是材料混合区域,使得晶粒取向更为随机。     

Corrosion and Cavitation Erosion Behaviours of Cast Nickel Aluminium Bronze in 3.5% NaCl Solution with Different Sulphide Concentrations

The effect of sulphide(Na_2S) concentration(SC) on the corrosion and cavitation erosion behaviours of a cast nickel aluminium bronze(NAB) in 3.5% NaCl solution is investigated in this study.The results show that when the SC exceeds 50 ppm,the hydrogen evolution reaction dominates the cathodic process,and a limiting current region appears in the anodic branch of the polarisation curve due to the formation of a copper sulphide film,which is a diffusion-controlled process.After longterm immersion,the increased mass loss rate of NAB with the sulphide additions of 20 and 50 ppm is attributed to the less protective films,which contains a mixture of copper oxides and sulphides.Moreover,NAB undergoes severe localised corrosion(selective phase corrosion,SPC) at the β' phases and eutectoid microstructure α+κ_Ⅲ.By comparison,NAB undergoes general corrosion and a copper sulphide film is formed in 100 and 200 ppm sulphide solutions.Cavitation erosion greatly increases the corrosion rate of NAB in all solutions and causes a negative potential shift in 3.5% NaCl solution due to the film destruction.However,a positive potential shift occurs in the solutions with SC higher than 50 ppm due to the accelerated mass transfer of the cathodic process.The cavitation erosion mass loss rate of NAB increases with the increase of SC.The occurrence of severe SPC decreases the phase boundary cohesion and causes brittle fracture under the cavitation impact.The corrosion-enhanced erosion is the most predominant factor for the cavitation erosion damage when the SC exceeds 50 ppm.     

Comparative studies of grain refinement of commercial purity Mg by CaO and Ca addition

ABSTRACT

The comparative studies of grain refinement of commercial purity Mg by CaO/Ca addition have been investigated by using TP-1 tests, optical microscope, XRD characterisation and TEM (STEM) observation along with EDX analysis. Experimental results showed that Ca/CaO addition significantly refines the grain structure of commercial purity Mg. Compared with Ca addition, CaO exhibits finer grain size and the average grain size remains invariable with further CaO addition. CaO addition is readily reduced to Ca by Mg melt and forms Mg₂Ca on the surface of MgO particles. First-principle calculations were used to understand the nucleation of Mg₂Ca layer by a coherent interface model calculating the work of adhesion and the interface energy between Mg₂Ca and α-Mg. The combination of experiments and calculations showed that the formation of Mg₂Ca layer on MgO facilitates the nucleation of α-Mg and then refines the grain structure by Ca or CaO addition.     

Effects of trace Cr on as-cast microstructure and microstructural evolution of semi-solid isothermal heat treatment ZC61 magnesium alloy

The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.     

Wearing and Corrosion Resistance of TAMZ Alloy Implanted by Carbon Ion in Hank’s Body Fluid

人体模拟体液Hank’s溶液中对碳离子注入TAMZ合金的耐蚀耐磨行为进行研究。结果表明,碳离子注入TAMZ合金表面形成含碳量1.07%的均匀改性层,碳离子注入层厚度达9 μm。碳离子注入后,TAMZ表面形成无序层膜,经XRD分析主要由TiC和Ti组成。Hank’s溶液中电化学测试结果表明,注入碳离子的TAMZ合金腐蚀电位升高、电荷转移电阻增大,阳极极化电流密度降低,改善了电化学性能。其原因归结于碳离子注入后碳化物的无序层膜的形成阻滞了合金元素的溶解,提高了膜层的耐蚀性能。Hank’s溶液中注入碳离子的TAMZ合金的摩擦系数和比磨损率均明显小于基体TAMZ合金,硬度提高;而且经摩擦的碳离子注入TAMZ合金比基体TAMZ合金的阳极极化电流密度小、电荷转移电阻大,表明碳离子注入改性层在人体模拟液环境中具有优良的耐磨、耐蚀性能     

电火花钻斜小孔特性研究

对电火花钻斜孔过程的放电状态进行了监测,并研究了电极长度对加工速度的影响。通过对钻斜孔过程放电状态的监测,发现电火花钻斜小孔可分为初钻阶段、钻孔阶段和击穿阶段。其中,初钻阶段和击穿阶段存在大量的开路、短路现象,加工速度慢;而钻孔阶段的正常放电概率大,加工速度快。随着电极因损耗而逐渐变短,加工速度呈增加的趋势,这主要是由于电极变短后,水头损失变小,内冲液流量增大,使排屑更顺畅,从而提高了加工效率。     

Zr及稀土Ce、La对铝电工圆杆性能的影响

通常在铝导线中加入Zr元素来提高其耐热性,但Zr的加入会严重降低导线的电导率,造成线损增加。试验研究了Zr与Ce、La稀土复合加入对铝电工圆杆组织和性能的影响。结果表明:Zr分别与稀土La、Ce互配加入都能使电工圆杆在电导率下降较少的情况下,强度有一定幅度的提高,这为高强高电导率耐热铝合金导线的研究作了初步探索。