Effect of D-fructose on the in-vitro corrosion behavior of AZ31 magnesium alloy in simulated body fluid

The effect of addingd-fructose to simulated body fluid(SBF) on the corrosion behavior of AZ31 magnesium(Mg) alloy at 37.C and at a pH of 7.4 was studied by potentiodynamic polarization(PDP), electrochemical impedance spectroscopy(EIS), potentiostatic polarization and hydrogen(H2) collecting techniques,Raman spectroscopy technique, scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), X-ray photoelectron spectroscopy analysis(XPS) and Fourier transformed infrared(FTIR). The results demonstrated that the addition of fructose enhanced the deposition of phosphates forming thick and compact corrosion products, which inhibited the transmission of aggressive ions into the Mg substrate. As a result, both the anodic dissolution of Mg and negative difference effect(NDE) were suppressed. Thus, the corrosion resistance of AZ31 Mgalloy in SBF was significantly improved.     

Organo-silane coatings for AZ31 magnesium alloy corrosion protection

The protective performances of coatings formed by organo-silanes with a long alkyl chain for AZ31 magnesium alloy corrosion protection were evaluated by electrochemical techniques. The coatings were formed in hydroalcoholic baths of octyl- or octadecyl-trimethoxy-silane, and hydrolyzed at different pH values.

The coatings formed at all the pH by the lower homologue were always porous and scarcely protective. Those built by the higher homologue were more corrosion resistant and the best results were observed when octadecyl-trimethoxy-silane was hydrolyzed at pH 5: in this case a thick, scarcely defective, layer was formed and no evident corrosion attack was observed after 1000 h immersion in 0.05 M Na₂SO₄ solution.     

Quantitative analysis on friction stress of hot-extruded AZ31 magnesium alloy at room temperature

Mg alloy AZ31 with ～79% (volume fraction of scattering less than 30°) basal-fiber texture through hot extrusion exhibits strong grain-size dependent yield strength. Samples with grain sizes varying from 4.5 to 22.3 μm were obtained by altering annealing time durations. The Hall-Petch relations of tension and compression are σ_0.2 = 86+200d^?1/2 and σ_0.2 = 17 + 327d^?1/2, respectively. Considering the correlation between grain orientation and deformation modes, a novel weighted average method of calculating friction stress σ₀ was proposed, and results of calculation agreed with the experimental ones, which can reasonably understand the yielding behavior in tension and compression.     

Effect of applied potential on the microstructure,composition and corrosion resistance evolution of fluoride conversion film on AZ31 magnesium alloy

AZ31 magnesium (Mg) alloy was potentiostatic polarized in 0.1?M deaerated KF solution with pH 7.5 from ?0.4?V to ?1.4?V with an interval of ?0.2?V. The polarization process was described by the potentiostatic current decay. The resultant film was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results demonstrated that the deposited film included a Mg(OH)₂/MgF₂ containing inner layer and a Mg(OH)₂/MgF₂/KMgF₃ comprising outer layer. The high polarized potential produced high content of MgF₂ but low content of KMgF₃ and thin film. Conversely, the low polarized potential produced small content of MgF₂ but high content of KMgF₃ and thick film. The optimal corrosion resistance of the deposited film was obtained at ?1.4?V, which was closely related with the content of MgF₂ and KMgF₃ and the film thickness.     

AZ31镁合金非等温拉深性能的研究

针对AZ31镁合金等温拉深性能差的问题,提出了AZ31镁合金的非等温拉深工艺.通过平底杯形冲头拉深试验研究了不同冲头温度和板料温度对AZ31镁合金非等温拉深性能的影响,确定了使AZ31镁合金具有最佳拉深性能的板料和冲头温度范围.实验结果表明,除了板料和冲头温度之外,拉深速度和润滑条件对AZ31镁合金的非等温拉深性能也有重要影响.     

电轧AZ31镁合金在模拟海水中腐蚀行为研究

为对比研究高能电脉冲轧制工艺和冷轧工艺对AZ31镁合金腐蚀性能的影响,采用腐蚀形貌观察、动电位极化测试、电化学阻抗谱与腐蚀速度测试等方法系统地研究了高能电脉冲轧制和冷轧AZ31镁合金带材在模拟海水(3.5%NaCl)中的腐蚀行为.结果表明:在同样变形量下,与冷轧AZ31镁合金相比,电轧AZ31镁合金的耐腐蚀性略有提高.这与电轧AZ31镁合金再结晶比例大,位错密度小,具有较低能态的位错组态及能形成较稳定的腐蚀产物膜有关.     

Effect of electromagnetic stirring and solution treatment on microstructure and properties of AZ31 magnesium alloy

Effect of electromagnetic stirring and solution treatment on the microstructural evolution and mechanical properties of AZ31 alloy are investigated in this study. Results show that the mechanical properties of AZ31 alloy are substantially increased after electromagnetic stirring and solution treatment. The tensile strength and elongation are 178 MPa and 19.6 % for AZ31 alloy prepared by electromagnetic stirring after solution treatment. A large number of twins and low angle boundaries are observed in the specimen after heat treatment, since the compressive stress on ( ) crystal plane become larger during quenching. The dislocation arrays, which produced by slip or climbing of dislocations, join together to form low angle boundaries.     

铸态AZ31镁合金板材等温轧制工艺及组织性能研究

为研究铸态AZ31镁合金轧制工艺及轧制后组织性能,通过试验得到不同道次和变形量对铸态AZ31镁合金板材显微组织和力学性能的影响规律,并采用扫描电子显微镜研究了轧制后板材组织.结果表明,铸态AZ31镁合金板材经等温4道次、等变形量轧制后,板材厚度由20mm变化到4.8 mm,抗拉强度和屈服强度分别达到275 MPa和18...     

Effect of 1.5 wt% tin addition on the properties of AZ31 magnesium alloy

In this paper, 1.5 wt%Sn was added to the AZ31 magnesium alloy aiming at improving the mechanical properties by using a low cost alloying element. Both alloys were prepared in the cast/heat treated (HT), rolled at 350 °C, rolled/heat treated at 400 °C and extruded at 350 °C. The results indicate that with addition of tin an improvement was obtained in both tensile strength and ductility of the AZ31 alloy in the cast/heat treated and in the extruded conditions. The yield and ultimate tensile strengths reached 98 MPa and 224 MPa respectively with 14 % elongation in the cast/heat treated condition while in the extruded condition these values were 212 MPa and 286 MPa with 20 % elongation. The tensile strength was even higher after rolling reaching 315 MPa for AZ31 with tin addition; however, as the material temperature during the last passes has decreased to relatively low values, the % elongation decreased to 1 %. After heat treatment at 400 °C for 2 hours the % elongation was restored and reached 12 %; this was accompanied by a decrease in tensile strength which reached 276 MPa. The results are discussed in relation to the microstructure evolution including grain size, phase identification, and volume fraction of phases.     

Forging of Mg‐Alloys AZ31 and AZ80

Mg‐wrought alloys recently became an engineer material of constantly increasing interest. The mechanical properties of extruded Mg‐feedstock of the alloys AZ80 and AZ31 indicate their suitability for automotive applications in form of high‐quality forgings. Therefore a detailed knowledge about the forming behaviour is of particular importance. In order to compare mechanical properties of available Mg‐feedstock qualities compression tests at room temperature have been carried out by applying batches of AZ31‐ and AZ80‐feedstock. Cylindrical specimens were made out of received continuously casted as well as extruded AZ31‐ and AZ80 ‐ rods. A quantitative analysis of Mg‐feedstock’s microstructure has been carried out. The characterization of the deformability of applied Mg‐feedstock under hot working conditions could be performed by means of uniaxial plain strain upsetting tests at temperatures between 300 and 450 °C as well as logarithmic strain rates of 10^‐1, 1 and 10s^‐1. It is shown that the chosen parameter range ensures an enhanced deformability of continuously as well as extruded Mg‐feedstock. The subsequently carried out determination of microstructural evolution could be related to obtained flow stress curves of applied batches of Mg‐feedstock. Furthermore, FVM/FEM‐systems have been employed in order to design a simplified geometry of heated forging dies suitable for forging tests. The tests have been carried out by means of a hydraulic press. During the tests their punch velocity has been varied between 1 and 40 mm/s. Hence numerically simulated results could be confirmed by practical tests. Exemplary forgings of a simplified shape were made out of all applied batches of Mg‐feedstock. No remarkable failures have been detected.     

热挤压工艺对AZ31镁合金晶粒大小及性能的影响

对商用AZ31镁合金挤压棒材进行了不同工艺参数的挤压变形,系统研究了挤压工艺参数对AZ31镁合金晶粒大小以及性能的影响,并对镁合金组织的微晶尺寸进行了金相定量分析.研究结果表明,热变形可有效细化晶粒,但对AZ31镁合金晶粒细化是有限度的;对已通过热挤压变形晶粒细化的AZ31镁合金进一步进行大的塑性变形,其晶粒不但没有进一步的细化反而比挤压前略有长大.     

热挤压AZ31镁合金的组织结构与蠕变行为

通过对热挤压态AZ31镁合金进行组织形貌观察、内摩擦应力测定及蠕变性能测试,研究了热挤压AZ31合金的组织结构和蠕变行为.结果表明:热挤压AZ31镁合金的组织具有带状结构特征,并沿轧制方向分布,且有β-Mg17Al12相在合金中弥散析出.蠕变期间,位错运动的内摩擦力有较强的温度敏感性,随温度增加,内应力值明显降低,致使合金具有较高的蠕变速率.合金在蠕变期间,大量位错的形成与运动是蠕变初期的变形机制;蠕变稳态阶段,高密度位错逐渐束集形成位错胞,进一步发生蠕变期间的动态再结晶.随裂纹在晶界处萌生使蠕变进入第三阶段,而裂纹沿晶界韧性撕裂扩展是合金的蠕变断裂机制.     

Rotation friction pressing riveting of AZ31 magnesium alloy sheet

A kind of joining method for magnesium alloys, rotation friction pressing riveting (RFPR), is proposed in this paper. In RFPR operation, a rivet with a plug rotating at high speed is brought to contact with the riveted sheets, generating frictional heat between the rivet and riveted sheets, which softens the sheet materials and enables the rivet to be drilled into the sheets under reduced force. When fully inserted, the rivet is stopped rotating, and the plug is immediately pressed into the shank of the rivet by a punch. The expansive deformation of the rivet shank occurs under the action of the plug, thereby forming a mechanical interlock between the rivet and the sheets to fasten the sheets together. The studies show that RFPR of AZ31 magnesium alloy sheet can be carried out at ambient temperature, and provides the joints with superior shear strength and fatigue property when compared with self-piercing riveting (SPR). The effects of the operating parameters of RFPR process on the quality of the joints were investigated in the study. The results shows that while the rivet rotation speed little affects the shear strength of RFPR joints, the punch pressure has a significant influence on the mechanical properties of the RFPR joints. A numerical analysis was also performed to understand the effect of the punch pressure on the interlock between the rivet and the sheets, and the stress and strain distribution inside the sheet materials around the rivet. The results show that the interlock increased with the punch pressure and there is residual compressive stress inside the sheet materials, which seems to explain the good fatigue property of RFPR joints observed.     

Surface modification of magnesium alloy AZ31 by hydrofluoric acid treatment and its effect on the corrosion behaviour

In the present study, the effect of hydrofluoric acid (HF) treatment on the surface composition and corrosion behaviour of the magnesium alloy AZ 31 was investigated. The HF treatment of the samples was performed with various concentrations and at different treatment times. The samples surfaces were analysed by Fourier transform infrared spectroscopy, optical emission spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The results showed the formation of hydroxides, oxides and compounds of the general formula Mg(OH)_xF_2 − x on the samples surfaces, as well as variations on impurities concentrations. The process led to distinct surfaces, each having its specific corrosion resistance, which was evaluated by electrochemical impedance spectroscopy and potentio-dynamic polarization. The most improved corrosion protection was achieved using the concentrations of 14 and 20 mol L^− 1 and 24 h of treatment time, resulting in corrosion rates 20 times lower than those of untreated samples. These two solutions also resulted in an improved corrosion protection for further polymeric coatings, showing that this treatment is an excellent pre-treatment for corrosion protective layers on magnesium alloys.     

Experimental investigation of pulse current on mechanical behaviour of AZ31 alloy

The effect of pulse current on the mechanical properties of AZ31 alloy is investigated through uniaxial tensile test at different temperatures. The electroplastic effect is evaluated by the change of ultimate strength. During tensile test, both microstructure evolution and fracture behaviour are sensitive to the applied deformation conditions. In this work, the influence of pulse current is discussed from the point of view of microstructure evolution and fracture characteristics. The experimental results show that the dynamic recrystallisation temperature of AZ31 is reduced by the pulse current and continuous dynamic recrystallisation is found at 100°C for tensile test with current. The data also indicate that the pulse current accelerates the precipitation and dissolved of the second phase particles in AZ31 alloy.     

Influence of neodymium on microstructure and mechanical properties of AZ31B wrought magnesium alloy

Abstract

The influences of rare earth neodymium on microstructure and mechanical properties of as cast and hot rolled AZ31B wrought magnesium alloy were investigated. The results show that the mechanical properties of both as cast and hot rolled AZ31B alloys decrease due to Nd addition. Nd reacts with Al to form Al₂Nd phase when Nd is added. Bulky and brittle Al₂Nd intermetallic degrades the mechanical properties. Moreover, the addition of Nd weakens the grain refining effect of Al on as cast AZ31B alloy, resulting in grain coarsening. Coarse grains also cause the decline of the mechanical properties of as cast AZ31B–Nd alloy. The negative influence of the bulky and brittle intermetallics on mechanical properties of AZ31B alloy can be relieved by large deformation because the intermetallics can be sufficiently broken up during the deformation process.     

Temperature evolution analysis of AZ31B magnesium alloy during quasi-static fracture

Fracture toughness of AZ31B magnesium alloy subjected to quasi-static loading was investigated by infrared thermography. The results showed that temperature evolution around the crack propagation path during fracture underwent three stages: initial steady stage, monotonic increase stage and final steady stage. The temperature increase at the beginning of stage II is nearly corresponding to the initiation of unstable crack propagation. And based on this phenomenon, a method applying infrared thermography to estimate fracture toughness of AZ31B magnesium alloy was proposed. Fracture toughness was calculated through infrared thermography, which was in good agreement with the result determined by traditional standard method. Finally, the fracture mechanism was investigated.     

AZ31镁合金温变形对其性能影响的研究

为了研究温变形对铸态AZ31镁合金力学性能的影响,在210～300℃温度范围内对均匀化后的合金进行了不同程度的平面应变压缩,并根据微观组织的演变对其进行了分析.结果表明:随变形温度的升高,在相同的变形程度下晶粒有长大的趋势,其抗拉强度增量下降;在同一温度下变形,强度增量随着变形程度的增加而增大,变形到一定程度时,呈现减小的趋势.在210℃下变形,当ε达到2.07时,其抗拉强度最大可达305MPa,较铸态提高近50%.表明AZ31合金温变形时,通过形变强化与细晶强化的合理组合,可获得细小均匀的等轴组织,大幅度提高镁合金的强度.     

AZ31B镁合金带材热轧过程组织均匀性及性能研究

本文开展了变形温度为300、350、400 ℃和总压下率分别为15%、30%、45%、60%的AZ31B镁合金带材热轧试验,分析了不同工艺参数对轧后带材的微观组织及力学性能的影响规律。研究表明:随着轧制温度的升高,再结晶百分数增加,晶粒细化显著,组织均匀性增强;当温度达到350 ℃时,由于中间退火保温导致再结晶晶粒长大,使温度进一步升高,对再结晶程度的影响减弱,轧后带材晶粒度和延伸率均有降低;相比温度参数,提升总压下率对晶粒细化效果更为显著,轧制温度为300 ℃,压下率为60%时近表面平均晶粒尺寸由10 μm细化至3.7 μm,中心层晶粒尺寸细化至4.9 μm,组织分布较为均匀;压下率的增加有效改善了组织均匀性,使轧后带材延伸率显著增加,拉伸断口的韧窝增多,且逐渐加深。     

Microstructures and tensile properties of AZ31 magnesium alloy by continuous extrusion forming process

The objective of this study is to investigate the possibility of continuous extrusion forming (Conform process) of AZ31 magnesium alloy. The results indicate that continuous extrusion forming can refine the structure, improve the degree of the structure homogeneity and change the crystal orientation of basal plane and hence enhance the ductility but decrease tensile strength at room temperature. The fracture mechanisms of the material prepared by Conform process change from the mixture of ductile and brittle to the full dimpled rupture compared with the conventional extrudate.