Anticorrosive magnesium phosphate coating on AZ31 magnesium alloy

A novel anticorrosive film with a thickness of approximately 50 μm was successfully coated on an AZ31 magnesium alloy by chemical and low-heat treatments (50 °C). The film was a single-phase system of newberyite (MgHPO₄•3H₂O) having an orthorhombic crystal structure. The corrosion current density of the newberyite film coated on the AZ31 magnesium alloy decreased by more than two orders of magnitude as compared to that of the AZ31 magnesium alloy. The static water contact angle of the newberyite film was less than 10°. The average value of the scratch critical load for the newberyite coating was estimated to be approximately 15 mN.     

镁及镁合金阻尼特性的研究进展

综述了镁及镁合金阻尼特性的研究进展及阻尼镁合金材料的研究现状,介绍了其阻尼性能的评价方法,阐明了其阻尼机制符合G-L位错钉扎模型、基面(0001)上的位错脱钉运动是造成镁合金在室温具有高应变振幅阻尼性能的主要原因,概述了应变振幅、温度、变形工艺、热处理、晶粒尺寸和取向以及合金元素对镁合金阻尼性能的影响.     

Warm incremental forming of magnesium alloy AZ31

Industrial application of magnesium alloy AZ31 is dramatically increasing due to the very competitive mechanical strength vs. weight ratio. On the other hand, AZ31 is very difficult to be formed at room temperature. In this study incremental forming of the above material is taken into account, with particular reference to formability limits. The role of the main process parameters on material formability was investigated through a wide experimental campaign and a rigorous statistical analysis.     

Mechanical spectroscopy of commercial AZ91 magnesium alloy

A damping peak at around 425 K for a frequency of about 1 Hz was found and it was correlated to the characteristic grain boundary peak of magnesium. An increase in the height of the grain boundary peak appears during the temperature cycles, controlled by the decrease of solute atoms in the matrix since the appearance of a precipitation process.     

双向双通道变通径挤压AZ31镁合金的显微组织及变形行为

在不同温度下,采用双向双通道变通径挤压(DDE)对AZ31镁合金进行挤压,研究该工艺对其组织、力学性能、拉压不对称性和断裂行为的影响。结果表明:与均匀态AZ31镁合金相比,挤压后所得试样的晶粒显著细化,力学性能和拉压不对称性得到改善;与采用等通道角挤压工艺多道次挤压试样的力学性能相比,该工艺具有一定的优势。此外,随着挤压温度的升高,晶粒尺寸逐渐增大,显微硬度、抗拉强度和压缩率逐渐降低。从250℃到450℃,晶粒尺寸从6μm增大到26μm,硬度值(HV)从67降低到56,抗压强度从400MPa降低到343MPa,压缩率从14.8%降低到9.7%。均匀态AZ31和挤压态AZ31的压缩断口均为穿晶断裂,前者断裂机理为脆性解理断裂,后者为韧脆结合型准解理断裂。     

等通道转角挤压处理的镁合金AZ31的低周疲劳行为

研究了一道次等通道转角挤压(ECAP)处理的镁合金AZ31挤压棒材的低周疲劳行为,结果表明:在塑性应变幡为0.5％时,材料表现出显著地循环软化;而在应变幅不大于0.2％时,基本表现为循环稳定或微弱的循环软化.疲劳裂纹主要萌生于细晶区,并沿着细晶区扩展,并导致最终的断裂.     

Effect of thermomechanical treatment on microstructure and hardness behavior of AZ63 magnesium alloy

Due to their high specifc strength and low density, magnesium alloys are widely used in many weight-saving applications. This research is aimed at investigating the microstructure and hardness of commercial AZ63 alloy specimens subjected to two diferent thermomechanical treatments (TMTs). For the first TMT, after solution treated at the temperature of 380 ℃ for 20 h, AZ63 alloy specimens were 5% cold worked by rolling process followed by ageing at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. In the second TMT, the specimens were solution treated at the temperature of 380 ℃ for 20 h, underwent 2% cold worked and quenched in water of 0 ℃. Half of the specimens were then 2% cold worked whilst the rest were rolled to 8% cold worked. All the specimens were then aged at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. Optical microscope was used to analyze the microstructures of the specimens. Hardness test was too conducted to measure the effect of the treatments on the specimens. Results show that two-step aging enhances the hardness of the specimens due to the distribution of the Beta-phase (Mg₁₇Al₁₂) in the alloy matrix. The results also reveal that, the best hardness from the first TMT was produced by specimen that was pre-aged at 150 ℃ whereas, in the second TMT, aging at 250 ℃　exhibited the best hardness values.     

Hot-compression constitutive relation of as-cast AZ31 magnesium alloy

In hot-compression process, the various factors have obvious effects on the deformation behavior of AZ31 magnesium alloy deformation behavior. To understand the hot-compression constitutive relation thoroughly, the stress-strain behavior of AZ31 magnesium alloy at various strain rates and different deformation temperatures were investigated under maximum strain of 60%. The microstructure of the experimental alloy was studied in the hot-compression procedure. The experimental results show that the relation of peak flow stress, strain rate and temperature can be described by Z parameter which contains Arrheniues item. The strain rate and the deformation temperature are the key parameters affecting deformation activation energy.     

工业态AZ31镁合金的超塑性变形行为

研究了工业态AZ31镁合金在温度 6 2 3～ 72 3K和应变速率 1× 10 -5～ 1× 10 -3 s-1范围内的超塑性变形行为。结果表明 ,工业态AZ31镁合金表现出良好的超塑性 ,其最高断裂延伸率达到 314%,应变速率敏感指数达 0 .4。显微组织观察和断口分析表明 ,工业态AZ31镁合金超塑变形主要由晶界滑动机制所控制 ,同时 ,动态再结晶也是合金超塑变形的一种协同机制。     

On the degradation mechanism of corrosion protective poly(ether imide) coatings on magnesium AZ31 alloy

In previous publications of the authors, good performance of poly(ether imide) as corrosion protective coatings for magnesium AZ31 alloy was reported. It was suggested that during the sample degradation magnesium hydroxide could react with the imide ring forming magnesium polyamate and polyamic acid, but this could not be experimentally confirmed. In the present letter, we confirm the occurrence of this reaction by infrared and X-ray photoelectron spectroscopy and discuss its influence in the corrosion behavior observed in electrochemical impedance spectroscopy tests.     

Surface oxidation of molten AZ91D magnesium alloy in air

The surface of a stagnant AZ91D alloy melt has been exposed to air under two oxidation conditions: at 610°C for 30 min and at 650°C for 10 s. After oxidising, the samples were sand quenched. The macroscopic morphology of the surfaces exhibited regions of non-nodular growth (in a layer manner) and regions of nodular growth. Additionally, the 610°C 30 min condition presented a region where localised combustion took place. The microscopic morphology of the surfaces and the nature of the surface reaction products have been analysed using field emission gun SEM and X-ray diffraction techniques, respectively. These results showed that all these morphologies, i.e. sponge-like, nodular and layer, were porous and therefore non-protective with respect to the evaporation and oxidation of Mg and Zn from the surface of the AZ91D alloy melt. In all these regions, MgO was the main oxidation product along with traces of ZnO and AlN.     

AZ31镁合金的各向异性及断裂行为

研究织构和异常长大晶粒对热轧AZ31镁合金力学各向异性和断裂行为的影响.在拉伸轴与板材的法向方向分别呈0°、15°、30°、45°、60°、75°和90°下进行单轴拉伸实验,观察不同角度下样品的拉伸各向异性.结果表明:由于{1012}孪晶的出现,在0°-30°时样品表现出较低的屈服强度;当角度大于45°时,样品的主要的变形机制为基面和柱面滑移;当角度低于60°时,宏观断口平行于大晶粒拉长的方向;在75°和90°时样品的宏观断口呈锯齿状.     

Corrosion behavior of pure Mg and AZ31 magnesium alloy

Protection of Metals and Physical Chemistry of Surfaces - Purpose of this article is to study corrosion behavior of pure magnesium and AZ31 magnesium alloy in electrolyte containing different...     

Strain amplitude-dependent internal friction of as-cast high damping magnesium alloy during cyclic vibration

An investigation on strain amplitude-dependent internal friction (IF) of an as-cast high damping Mg-7 wt% Ni alloy was carried out. In the range of our tested strain amplitudes, whether the strain amplitude is increasing or decreasing, the strain amplitude-dependent IF curve can be divided into two stages: one is the strain amplitude weakly dependent part and the other is the strain amplitude strongly dependent part. However, after several cyclic vibrations, the IF values measured during the strain amplitude increasing are smaller than those obtained during the strain amplitude decreasing. The phenomenon is also observed at 100 ℃. Partial dislocations generate a short-range slip under the cyclic stress to be responsible for it.     

Stannate and permanganate conversion coatings on AZ31 magnesium alloy

The formation of stannate and permanganate–phosphate conversion coatings on AZ31 magnesium alloy was investigated in situ by EIS measurements and their protective performances were studied by different electrochemical techniques in diluted (0.05 M) sodium sulphate solution.The influence that short or long treatment times exert on the performances of such conversion coatings is discussed. While permanganate–phosphate baths always built layers characterized by penetrating cracks, long stannate baths produced layers without interconnected porosity, but were defective. This accounted for the initial greater protectiveness achieved with the stannate treatment; nevertheless, the easy penetration of the electrolytic solution through such a layer quickly decreased its corrosion resistance.     

Annealing behavior of rolled AZ31 alloy sheet

The annealed microstructures of the rolled AZ31 alloy sheets were examined by using light optical microscopy. The mechanical properties were measured by tensile testing, with their crystal orientations analyzed by X-ray diffraction （XRD）. After the annealing treatment, the elongated grains were transformed to equiaxed grains with uniform and homogeneous structures. The changes of microstructure decreased the yield strength and enhanced the elongation. The analysis of XRD shows that the AZ31 alloy sheet possesses intense basal-texture, which is weakened during the recrystallization while reinforced during the grain growth. The intense basal-texture induces low ductility, which hence makes the further rolling more difficult. The results indicate that the optimum annealing treatment during AZ31 alloys sheet rolling is at about 300 ℃ for 60-120 min.     

Grain refinement of AZ31 magnesium alloy by new Al-Ti-C master alloys

New Al₄C₃-containing Al-Ti-C master alloys (Al-0.6Ti-1C and Al-1Ti-1C) were developed by introducing Ti element into Al-C melt using melt reaction method, in which most of the TiC particles distribute around Al₄C₃ particles. It is believed that most of the C firstly reacts with Al melt and form Al₄C₃ particles by the reaction Al(l)+C(s)→Al₄C₃(s), and after adding Ti into the Al-C melt, the size of Al₄C₃ particles is decreased and the distribution of Al₄C₃ is improved through the reaction Ti(solute)+Al₄C₃(s)→TiC(s)+Al(l). With the addition of 1% Al-1Ti-1C master alloy, the average grain size of AZ31 is reduced sharply from 850 μm to 200 μm, and the grain morphology of α-Mg transits from a fully-developed equiaxed dendritic structure to a petal-like shape. Al-C-O-Mn-Fe compounds are proposed to be potent nucleating substrates for primary Mg. Appropriate addition of Ti is believed to increase the grain refinement efficiency of Al₄C₃-containing Al-Ti-C master alloys in AZ31 alloy.