关键词： AZ31B镁合金   剪切旋压   差温旋压  

摘要： 分别进行了AZ31B镁合金轧板等温剪切旋压成形和差温剪切旋压成形实验,对两种成形条件下的工件微观组织和力学性能进行了对比分析。结果表明:200~300℃变形时,镁合金轧板具有良好的等温剪切旋压和差温剪切旋压可成形性;在热旋压成形时,旋压件发生了晶粒细化,但随着旋压温度上升,两种成形方式的旋压件平均晶粒尺寸均增加。在200℃旋压成形时,差温剪切旋压件组织更加细小,力学性能优于等温剪切旋压工件,其轧向(RD)与横向(TD)方向的屈服强度分别为251、233 MPa,抗拉强度分别为304、299 MPa,伸长率分别为21.1%、21.8%;随着旋压温度增至300℃,差温旋压件与等温旋压件的组织状态和力学性能趋于一致。

关键词： magnesium alloy   cyclic plasticity   macroscopic experiments   microscopic observations   constitutive model  

摘要： Fatigue analysis has always been a concern in the design and assessment of Mg alloy structure components subjected to cyclic loading,and research on the cyclic plasticity is fundamental to investigate the corresponding fatigue ***,this work reviews the progress in the cyclic plasticity of Mg ***,the existing macroscopic and microscopic experimental results of Mg alloys are ***,corresponding macroscopic phenomenological constitutive models and crystal plasticity-based models are ***,some conclusions and recommended topics on the cyclic plasticity of Mg alloys are provided to boost the further development and application of Mg alloys.

关键词： 镁合金   筒形件   复合铸型   铸造工艺   顺序凝固  

摘要： 针对一种材质为GW63K的复杂薄壁镁合金筒形件的结构特点和工艺难点,开展复合铸型铸造工艺研究。根据铸件结构,设计了基于不同型砂的复合铸型铸造工艺,利用ProCAST软件进行数值模拟仿真,并根据模拟结果进行凝固顺序调整,优化铸造工艺,最终达到顺序凝固的目的。结果表明,复合铸型铸造工艺条件下的铸件内部品质达到了HB7780-2005中Ⅰ类铸件要求,T6态力学性能满足抗拉强度≥280 MPa,伸长率≥3%的要求。

关键词： 空化   纳米粒子   强化   扫描电镜   X射线光电子能谱  

摘要： 通过空化泡溃灭产生的微射流促使Al_(2)O_(3)纳米粒子对镁合金进行冲击强化。采用显微硬度仪、扫描电镜(SEM)、X射线光电子能谱(XPS)对强化后的样品硬度、表面形貌、元素含量与化学态等参数进行分析。结果表明,强化5 min后,通过SEM发现在样品表面出现纳米级颗粒,结合XPS测试、发现样品中Al_(2)O_(3)含量明显增多,表明Al_(2)O_(3)粒子渗入表面,将其硬度提高了29.1 HV。推测强化作用机制为空泡溃灭的能量传递给Al_(2)O_(3)粒子,继而由Al_(2)O_(3)粒子冲击样品表面,因此样品承受的冲击更加柔性,且Al_(2)O_(3)纳米粒子自身的强度、硬度等性能较好,渗入样品表面后能够进一步提升强化效果。

关键词： Zerilli-Armstrong   Orthogonal cutting   Flow stress   Magnesium   HCP   AZ31B  

摘要： This work reports on a methodology to extend Oxley's analysis of the thick shear zone to account for HCP materials. Ultimately, the work extracts Zerilli-Armstrong (ZA) constitutive equation' material parameters for AZ31B, an HCP crystal structure magnesium-based alloy. The methodology for accomplishing this utilizes three tasks namely: 1) Extension of thick shear zone approach for machining force simulation to account for Zerilli-Armstrong HCP material model, 2) measure cutting and thrust edge forces from orthogonal cutting tests (uncut chip thickness and cutting speed values varying between 0.05 and 0.4 mm/rev and 50-400 m/min, respectively), and 3) numerically determine updated material model parameters for AZ31B by minimizing the difference between the methodology-predicted forces and those experimentally measured. Comparing numerical data with the experiments, the determined AZ31B material model with updated parameters yielded predictability of R-2 of 0.94 and 0.91 for cutting and thrust forces, respectively. Additional validations were conducted by favorably comparing flow stress numerical predictions for AZ31B with literature-published histories at wide operating ranges of temperature, strain, and strain rate values. The presented methodology for finding HCP Zerilli-Armstrong material model parameters based on orthogonal cutting tests may serve as complementary alternative to time-consuming tension-compression flow stress experiments.

关键词： electrodeposition film   magnesium alloy   quantum chemical calculations   superhydrophobic surface  

摘要： In this study, the superhydrophobic surface with SiO2 nanoparticles and corrosion-resisting property was prepared on magnesium alloy substrate by a simple one-step sol-gel electrodeposition. The influence of electrodeposition time on hydrophobicity and morphology of the magnesium alloy surface was discussed. The molecular dynamics simulations were conducted to provide an insight into the interactions between the C16H33Si(OH)(3) molecules and the magnesium surface. The results of frontier molecular orbital and Fukui function distributions indicated that the silicon hydroxyl of C16H33Si(OH)(3) was the probable reactive site via sharing electrons with metal atoms for the adsorption on the magnesium surface. Quantum chemical calculations indicated that the coordinate bonds could be formed between C16H33Si(OH)(3) molecule and unoccupied orbital of metal atom, which led to the active adsorption on the magnesium surface and generate the superhydrophobic surface. The results showed that the superhydrophobic surface could significantly improve the corrosion resistance compared with the pristine magnesium alloy in 3.5 wt.% NaCl solution.

关键词： electroless Ni-P coating   F   O ratio   magnesium alloy   pickling time  

摘要： In this study, a simple pickling process in H(3)PO(4)and NH(4)HF(2)solution was used for electroless Ni-P plating on AZ61 magnesium alloy. It is found that the corrosion rate of magnesium alloy during pickling significantly decreased because NH(4)HF(2)was added into H(3)PO(4)pickling solution. Ni-P coating plated only with pickling process shows poor adhesion because of the low F/O ratio of the substrate surface. However, F/O ratio, adhesion, and corrosion resistance of Ni-P coating are obviously enhanced after pickling followed by activation. The optimal pretreatment process is pickling for 120 s and activation for 4 min, under which the Ni-P coating has an optimum F/O ratio of 1.8 and the coating gets a dense structure, better adhesion, and higher corrosion resistance.

关键词： Magnesium alloys   fine grains   hardness   tensile strength   wear  

摘要： ZE41 magnesium alloy was successfully produced by friction stir processing and grain refinement was achieved from a starting size of 107 mu m +/- 6.7 mu m to 3.5 mu m +/- 1.5 mu m. MgZn intermetallic which was appeared as network like structure at the grain boundaries before friction stir processing was greatly affected due to the severe plastic deformation and broken as small particles as observed from the microstructural studies. Higher hardness (approximate to 30 %) was measured for the fine grained ZE41 magnesium alloy compared with the base alloy due to the grain refinement. From the tensile tests, yield strength and ultimate tensile strength was significantly increased at the cost of decreased ductility reflected in lower strain for the fine grained ZE41 compared with the base alloy. Wear studies showed higher coefficient of friction and lower mass loss for the grain refined ZE41 magnesium alloy. From the results, it can be understood that the grain refinement achieved by friction stir processing has a profound influence on enhancing the mechanical and tribological properties of ZE41 magnesium alloy.

关键词： Magnesium alloy   Aging-treatment   Mg17Al12 precipitates   Quantitative analysis   Corrosion rate  

摘要： Although qualitative investigations have been performed on the effects of discontinuous and continuous Mg17Al12 precipitates (DP and CP, respectively) on the corrosion resistance of AZ91 alloy, it is not clear whether the change in the corrosion resistance (i.e., an improvement or deterioration) is due to the DP, CP, or the different corrosion experimental conditions used. Herein, the effects of the DP and CP produced by an agingtreatment on the corrosion resistance of the AZ91D Mg alloy were systemically investigated in the same corrosion test condition (i.e. 3.5 wt% NaCl). The morphologies of the DP and CP were controlled by changing the aging-treatment conditions. The area fraction of the DP, the number of CPs per unit area, and the average length of the CPs were quantified as microstructural factors. A quantitative correlation analysis between the corrosion rate and the quantified microstructural factors revealed that the corrosion resistance of the aging-treated AZ91D Mg alloy depended on the DP and CP connectivities. DP with low connectivity accelerated the corrosion by acting as a galvanic source, while DP with high connectivity along the grain boundary functioned as a corrosion barrier, resulting in a reduced corrosion rate. Finely precipitated CPs inside the alloy grains always functioned as a corrosion barrier regardless of their amount and distribution. As the CP connectivity increased, the corrosion rate decreased, and the macroscopic corrosion morphology changed from local to uniform.

关键词： failure analysis   magnesium alloy   mechanical properties   medium entropy alloy   microstructure analysis  

摘要： The present study focused on the development of magnesium-based medium entropy alloy (Mg MEA). The multicomponent alloy with a composition, Mg62Li13Zn12Cu10Y3 (at.%), was processed using disintegrated melt deposition technique. The reported medium entropy alloys based on light metals, such as aluminum and magnesium, exhibit very low plasticity, and only cast alloys' properties were investigated. Currently developed Mg MEA showed an appreciable plasticity of 13.9% in as-cast condition. Secondary processing such as extrusion was applicable on the cast alloy due to its high deformability. A change in intermetallics morphology from continuous pattern in cast alloy to discontinuous pattern in extruded alloy was observed. In line with the change in microstructure, remarkably improved compressive properties were realized in extruded alloy as compared to cast alloy. Compressive strength and plasticity increased from 444 MPa and 13.9% in cast alloy to 675 MPa and 32.7% in extruded alloy. Previously reported lightweight MEAs exhibited a limited plasticity up to 6.5% in the cast form. The current lightweight Mg MEA reached a plasticity of more than twice of cast alloy and more than five times in the case of extruded alloy when compared to reported MEAs' plasticity in open literature. Unlike reported MEAs, currently developed Mg MEA revealed a relatively simple microstructure with three major phases. From the alloy design perspective, a large atomic size difference (delta: 8.49%) in the alloy was the main cause for the intermetallic formation. However, multiple phase formation was mitigated due to the suitable mixing enthalpy (Delta H-mix: - 4.52 kJ/mol). This counterbalancing effect from mixing enthalpy led to a simple microstructure, thereby enhancing the mechanical properties in the currently developed Mg MEA.