Evolution of rotated Brass texture by cross rolling: implications on formability

In the present work, the possibilities of tailoring crystallographic texture via cross rolling are presented. It is shown that a strong rotated Brass texture develops upon cross rolling in aluminium alloys which also remains intact during the subsequent recrystallisation annealing treatment. The governing mechanisms behind the evolution of deformation and recrystallisation texture are discussed in terms of effect of strain path on stability of deformation texture components and strain-induced boundary migration mechanism, respectively. In addition, the likelihood of rotated Brass texture having a positive effect on formability is discussed in terms of sluggish cross-slip criteria as the rotated Brass texture presents a unique scenario where cross-slip is inhibited along all the three principal directions.     

Particle size reduction of RDX by sequential application of solvent–antisolvent recrystallization and mechanical methods

ABSTRACT

Solvent–antisolvent recrystallization produced ~8 µm average size RDX particles (UF-RDX) that were subsequently subjected to mechanical methods of ultrasonication and ball-milling to find further achievable reduction in particle size. Long duration ultrasonication for 20 h and 300 rpm ball milling for 4 h of UF-RDX decreased its average particle size to ~2 µm. RDX produced by all the three processes (solvent–antisolvent recrystallization, ultrasonication and ball-milling) was similar to coarser RDX in structure and thermal decomposition behavior. However, UF-RDX produced by solvent–antisolvent recrystallization was significantly less impact sensitive than that produced by ball-milling and ultrasonication. The issues of residual solvent and the metal contamination during RDX processing were addressed by process parameter optimization. Solvent–antisolvent recrystallization and mechanical methods even when used sequentially could not bring average particle size of RDX to nano-scale.     

Effects of metal oxide nanoparticles on combustion and gas-generating performance of NaN3/Al composite powders ignited using a microhotplate platform

We investigated the effects of different metal oxide (MO) nanoparticles (e.g., CuO, KIO₄, Fe₂O₃) on the combustion and gas-generating characteristics of sodium azide microparticle (NaN₃ MP; gas-generating agent) and aluminum nanoparticle (Al NP; heat source) composite powders. The NaN₃ MP/Al NP/MO NP composite powders were stably ignited using a microhotplate (MHP) heater. The addition of CuO and KIO₄ to the NaN₃ MP/Al NP composite powders resulted in relatively high burn rates and high pressurization rates upon MHP-assisted ignition. This suggests that the highly reactive CuO and KIO₄ NPs significantly increased the combustion of the Al NPs; as a result, sufficient heat energy was generated via the active aluminothermic reaction to thermally decompose the NaN₃ MPs. Finally, the gas generating properties of NaN₃ MP/Al NP composite powders mixed with various MO NPs were tested using homemade inflatable small airbags. The airbags were fully inflated within ~20 ms when CuO and KIO₄ NPs were added to the NaN₃ MP/Al NP composite powders. However, the addition of Fe₂O₃ NPs to the NaN₃ MP/Al NP composite powder resulted in a slow and only partial inflation of the airbag due to an incomplete aluminothermic reaction, which was due to a slow combustion reaction between the Al NPs and relatively weak oxidizer of the Fe₂O₃ NPs. This suggests that the rapid, stable, and complete thermal decomposition of NaN₃ MP/Al NP composites can be effectively achieved by employing highly reactive nanoscale oxidizers.     

石墨烯对搅拌摩擦加工铝基复合材料性能的影响

采用结合粉末工艺的两步法搅拌摩擦加工制备石墨烯增强铝基复合材料,研究了石墨烯添加量对复合材料力学性能和导电性能的影响。结果表明,石墨烯的添加对铝基复合材料性能有明显的影响,随石墨烯添加量增加,复合材料的硬度逐渐提高、塑性持续下降,而抗拉强度和电导率均呈先增后减的趋势。石墨烯体积分数为3.7%时,复合材料的抗拉强度最高,达到146.5 MPa,与同等加工条件下的纯铝相比,提高了78.7%,而石墨烯体积分数为1.3%时,复合材料的电导率最高,达到30.62 MS/m,较同等加工条件下的纯铝基体提高了53.4%。     

直接激光沉积Al2O3增强NiCrAlY涂层的微观组织及力学性能

目的改善NiCrAlY涂层微观组织并提高其力学性能。方法采用直接激光沉积方法制备100%NiCrAlY、NiCrAlY+10%Al_2O_3和Ni CrAlY+20%Al_2O_3三种样件,分别利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、X射线能量色散谱仪(EDS)、电子探针X射线显微分析仪(EPMA),对不同成分样件进行相组成分析、微观组织观察以及元素组成检测,使用维式显微硬度测试计和万能摩擦磨损试验机,分别检测各个涂层的显微硬度和摩擦系数。结果在NiCrAlY中添加Al_2O_3后,Al_2O_3以不规则形状或球形分布在晶内或者晶界处,其尺寸小于2μm。三种复合涂层样件均由γ-Ni和β-NiAl相组成,添加Al_2O_3陶瓷颗粒后,涂层一次枝晶臂间距均减小,且Ni-Y相显著减少,Y2O3陶瓷颗粒弥散分布在基体的晶内与晶界处。NiCrAlY、NiCrAlY+10%Al_2O_3和NiCrAlY+20%Al_2O_3涂层的平均硬度分别为(440.69±30)HV0.2、(482.18±30)HV0.2和(453.09±20)HV0.2,100%NiCrAlY、NiCrAlY+10%Al_2O_3和NiCrAlY+20%Al_2O_3涂层的摩擦系数分别为0.77、0.55和0.52。结论加入Al_2O_3后,基体晶粒有一定程度的细化。在晶粒细化作用以及陶瓷颗粒弥散作用下,涂层的显微硬度有所提高,其中NiCrAlY+10%Al_2O_3的硬度最高,相比NiCrAlY基体提高了约9.5%。此外,发现添加Al_2O_3后,NiCrAlY+10%Al_2O_3和NiCrAlY+20%Al_2O_3样件的摩擦系数比NiCrAlY样件下降均超过25%,其中NiCrAlY+10%Al_2O_3样件的磨损量最小,相对于NiCrAlY涂层下降了近13.5%,耐磨性明显改善。     

超声辅助对激光熔覆Al2O3-ZrO2陶瓷涂层力学性能的影响

目的 探究超声辅助对钛合金表面激光熔覆Al2O3-ZrO2陶瓷涂层力学性能的影响。方法 使用COMSOL Multiphysics仿真软件，探究熔覆工件中有无超声作用下流场的变化，并将超声波直接引入熔池微区，研究超声辅助对Al2O3-ZrO2陶瓷涂层截面形貌、微观组织、元素分布、显微硬度和摩擦磨损性能的影响。结果 仿真结果表明，无超声时熔池横截面涡流大小呈对称状，流速较为缓慢，超声辅助下熔池截面的声速大小瞬时变化，熔池内流体的流速提高。实验结果表明，超声辅助下，熔覆层的截面形貌发生了一些变化，但抑制了熔覆层裂纹的产生。熔覆层晶粒尺寸细化，尤其是当激光功率为1700 W时，晶粒尺寸最小且相对更加致密;熔覆层内元素分布更加均匀，且界面效应降低。熔覆层的力学性能提高，激光功率为1700 W时，熔覆层平均显微硬度值为979.4HV0.2，相同激光功率下，超声辅助的熔覆层具有更大的平均显微硬度值。超声辅助下熔覆层的摩擦系数和波动幅值都较小，激光功率为1700 W时的摩擦系数最小(约为0.329)且波动较为平稳。结论 超声波直接引入熔池微区可以有效提高熔池的流动性，同时细化了晶粒，均匀化了元素分布，提高了熔覆层的力学性能。     

Ti-20Al-22Nb合金的凝固组织转变及力学行为

采用熔模铸造方法制备了名义成分为Ti-20Al-22Nb(at%)的合金,分别对铸态、热等静压及退火态进行了显微组织及室温拉伸性能分析。结果显示,合金由β基体、针状α2相及少量O相组成的,铸态下为粗大的魏氏组织,由于非平衡凝固,原始晶粒内部组织转变不完全,组织中的疏松缺陷及组织不均匀导致合金低的塑性；经过α2+β/B2两相区热等静压消除了疏松缺陷,原始晶粒内部充分析出细小针状的α2相,组织均匀性提高,合金的拉伸延伸率由2%提高到5%；经过α2+/B2+O三相区退火热处理,过饱和β相向平衡态转变,通过包析转变β/B2+α2→O,在针状α2相周围形成环带状O相,合金的延伸率提高到11%。     

Relationship between amounts of low-melting-point eutectics and hot tearing susceptibility of ternary Al−Cu−Mg alloys during solidification

A systematical study on the relationship between the amounts of different eutectic phases especially the low-melting-point (LMP) eutectics and the hot tearing susceptibility of ternary Al−Cu−Mg alloys during solidification was performed. By controlling the concentrations of major alloying elements (Cu, Mg), the amounts of LMP eutectics at the final stages of solidification were varied and the corresponding hot tearing susceptibility (HTS) was determined. The results showed that the Al−4.6Cu−0.4Mg (wt.%) alloy, which contained the smallest fraction of LMP eutectics among the investigated alloys, was observed to be the most susceptible to hot tearing. With the amount of total residual liquid being approximately the same in the alloys, the hot tearing resistance is considered to be closely related to the amounts of LMP eutectics. Specifically, the higher the amount of LMP eutectics was, the lower the HTS of the alloy was. Further, the potential mechanism of low HTS for alloys with high amounts of LMP eutectics among ternary Al−Cu−Mg alloys was discussed in terms of feeding ability and permeability as well as total viscosity evolution during solidification.     

Microstructure and mechanical properties of squeeze-cast Al−5.0Mg−3.0Zn−1.0Cu alloys in solution-treated and aged conditions

The microstructure and mechanical properties at different depths of squeeze-cast, solution-treated and aged Al−5.0Mg−3.0Zn−1.0Cu alloy were investigated. For squeeze-cast alloy, from casting surface to interior, the grain size of α(Al) matrix and width of T-Mg₃₂(AlZnCu)₄₉ phase increase significantly, while the volume fraction of T phase decreases. The related mechanical properties including ultimate tensile strength (UTS) and elongation decrease from 243.7 MPa and 2.3% to 217.9 MPa and 1.4%, respectively. After solution treatment at 470 °C for 36 h, T phase is dissolved into matrix, and the grain size increases so that the UTS and elongation from surface to interior are respectively reduced from 387.8 MPa and 18.6% to 348.9 MPa and 13.9%. After further peak-aging at 120 °C for 24 h, numerous G.P. II zone and η′ phase precipitate in matrix. Consequently, UTS values of the surface and interior increase to 449.5 and 421.4 MPa, while elongation values decrease to 12.5% and 8.1%, respectively.     

Fatigue strength and microstructure evaluation of Al 7050 alloy wires recycled by spray forming,extrusion and rotary swaging

Recycled high-strength aluminum alloys have limited use as structural materials due to poor mechanical properties. Spray forming remelting followed by hot extrusion is a promising route for reprocessing 7xxx alloys. The 7050 alloy machining chips were spray formed, hot extruded, rotary swaged and heat-treated in order to improve mechanical properties. Microstructures, tensile properties and fatigue strength results for a 2.7 mm-diameter recycled wire are presented. Secondary phases and precipitates were investigated by XRD, SEM, EBSD, TEM and DSC. As-swaged and heat-treated (solution and aging) conditions were evaluated. Mechanical properties of both conditions outperformed AA7050 aerospace specification. Substantial grain refinement resulted from the extensive plastic deformation imposed by rotary swaging. Refined micrometric and sub-micrometric Al grains, as well as coarse and fine intermetallic precipitates were observed. Subsequent solution treatment resulted in a homogeneous, recrystallized and equiaxed microstructure with grain size of 9 μm. Nanoscale GP(I) zones and η′ phase precipitates formed after aging at 120 °C, imparting higher tensile (586 MPa) and fatigue (198 MPa) strengths.