Corrosion protection of AZ31 magnesium alloy by silane film of partly hydrolysed BTESPT

Abstract

The corrosion protective behaviour of bis-[triethoxysilylpropyl]tetrasulphide (BTESPT) silane film formed by partly hydrolysed BTESPT on AZ31 Mg alloy was investigated. Fourier transform infrared spectroscopy (FTIR) was used for structural characterisation of the silane film. Scanning electron microscope (SEM) and energy dispersive X-ray (EDS) analysis were used for observation of surface morphology and elements analysis of the film. The corrosion behaviours of bare and the silane treated AZ31 Mg alloy in 3·5 wt-%NaCl solution were studied using electrochemical polarisation test, electrochemical impedance spectroscopy (EIS) and immersion test. The results demonstrate that bare AZ31 Mg alloy endures severe corrosion even in NaCl water solution at pH 12, although the corrosion is lighter than that in neutral and acidic NaCl water solution, and that the BTESPT silane film can improve the corrosion protection performances of AZ31 Mg alloy and a lower corrosion rate correlated with higher pH.     

AZ31镁合金表面碱性化学镀镍工艺研究

试验研究了AZ31镁合金表面碱性化学镀镍工艺。采用扫描电镜(SEM)、能谱成分分析(EDS)和X射线衍射(XRD)等方法对镀镍层的表面形貌、镀层成分及物相结构进行了分析,并测定了AZ31镁合金及镀层在w(NaCl)=3.5%的水溶液中的腐蚀电位和极化曲线,以此评价镀层的耐腐蚀性能。结果表明,预镀镍层为晶格畸变的晶态低磷镀层,二次镀镍层为非晶态高磷镀层,镁合金表面腐蚀电位在化学镀镍后明显升高,二次镀镍后钝化电位范围明显扩大,其耐腐蚀性能明显优于预镀镍层的。     

AZ31镁合金磁控溅射镀铝膜的性能研究

采用超真空磁控溅射镀膜设备在AZ31镁合金表面进行了铝保护膜的镀覆,利用辉光放电光谱分析和纳米压痕/划痕试验技术,研究了镀层的成分和显微力学性能随薄膜深度的分布。结果表明,铝镀层在镁合金基体表面形成,镀层和基体之间存在混融的过渡层,铝镀层的表面硬度、弹性模量等高于镁合金基体的,并随深度增加而递减,膜层与基体结合良好并表现出一定塑性,镀铝膜有利于镁合金表面防护层的形成。     

AZ31镁合金铸坯均匀化退火

研究了一种新的均匀化退火工艺对AZ31镁合金铸坯组织转变和成分均匀化的影响,保温温度为530、540和550 ℃以及保温时间为30、60和90 min.结果表明,AZ31镁合金在固相线温度以下应尽可能提高退火温度,同时缩短退火时间可使铸坯达到较好的均匀化效果,消除大部分枝晶偏析,γ-Mg_(17)Al_(12)相在α-Mg基体上呈细小的颗粒状分布; AZ31镁合金铸锭的优化退火工艺为540 ℃保温60 min.     

Fabrication of Cr coating on AZ31 magnesium alloy by magnetron sputtering

Chromium-plating is considered an effective method to improve surface properties of metal materials.Magnetron sputtering was applied to prepare Cr coating on AZ31 magnesium alloy and the influence of bias voltage on properties of Cr coating was investigated.The obtained coatings present an(110) preferred texture and have a developed columnar structure.With increasing bias voltage,the surface structure of Cr coating becomes denser.All of the Cr-coated AZ31 have much higher surface microhardness than bare ...     

AZ31镁合金板材等温弯曲实验研究

对AZ31镁合金板材的等温弯曲变形过程进行了数值模拟,分析了其变形特点以及金属流动规律,确定了合理的变形参数,即弯曲凸模半径为8 mm,凸模间距为38 mm。同时,研制了AZ31镁合金板材的等温弯曲实验装置,并对AZ31镁合金板材在不同变形温度下进行了不同道次的等温弯曲实验研究,分析了镁合金板材微观组织的变化规律。AZ31镁合金板材经过等温弯曲变形后,其室温伸长率达到17.1%,而原始AZ31镁合金板材的室温伸长率为12.4%,提高了42%。     

Enhanced corrosion performance of magnesium phosphate conversion coating on AZ31 magnesium alloy

Magnesium phosphate conversion coating (MPCC) was fabricated on AZ31 magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg²⁺ and PO^3?₄ ions. The MPCC on AZ31 Mg alloy showed micro-cracks structure and a uniform thickness with the thickness of about 2.5 µm after 20 min of phosphating treatment. The composition analyzed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the coating consisted of magnesium phosphate and magnesium hydroxide/oxide compounds. The MPCC showed a significant protective effect on AZ31 Mg alloy. The corrosion current of MPCC was reduced to about 3% of that of the uncoated surface and the time for the deterioration process during immersion in 0.5 mol/L NaCl solution improved from about 10 min to about 24 h.     

镁合金AZ31轧制板材的单向拉伸行为

通过单向拉伸试验研究了AZ31镁合金轧制板在不同温度和应变速率下的力学性能。根据镁合金在50℃~400℃范围内的单向拉伸曲线分析结果,找出AZ31镁合金的抗拉强度、伸长率随变形温度、变形速度的变化规律。结果表明:AZ31镁合金轧制板的塑性随着应变速率的降低有明显提高;温度的升高可明显改善轧制板的塑性;当应变速率为1.5×10-2s-1、温度为400℃时,伸长率达到123.9%。     

AZ31变形镁合金轧制工艺初探

研究了板坯加热温度、退火温度以及冷轧道次加工率对AZ31变形镁合金轧制能力的影响.结果表明,当加热温度为350℃,轧制速度为0.4m/s时,AZ31镁合金板材的热轧道次极限加工率可以达到34.62%(无裂纹)和59.23%(无表面裂纹);将热轧态板材分别在250℃～350℃温度,退火40min后,板材显微组织中晶粒大小均匀,维持在5μm～6μm水平;板材具有良好的综合力学性能,其抗拉强度为:230Pa～240MPa,屈服强度为:135MPa～175MPa,延伸率为:12%～15%.当采用350℃×40min退火后,板材在冷轧道次加工率为5%～10%时,总加工率可以达到40%以上.     

Preparation and corrosion resistance of superhydrophobic coatings on AZ31 magnesium alloy

In order to improve the corrosion resistance of the Mg alloys, the superhydrophobic coatings on AZ31 Mg alloy were prepared by a two-step process of micro-arc oxidation treatment and superhydrophobic treatment in stearic acid ethanol solution. The effects of voltages, frequencies and treatment time on the contact angle of the superhydrophobic treated sample were investigated. The results showed that with increasing the voltage, frequency and treatment time, all of the contact angles of the superhydrophobic treated sample increased first, and then decreased, reaching the maximum values at 350 V, 1000 Hz and 5 min, respectively. The optimal superhydrophobic coating was mainly composed of MgO and Mg₂SiO₄ phases, with the pore diameter of ～900 nm, the thickness of ～6.86 μm and the contact angle of 156.96°. The corrosion current density of the superhydrophobic AZ31 sample decreased by three orders of magnitude, and the amount of hydrogen evolution decreased by 94.77% compared with that of the AZ31 substrate sample.     

Preparation of AZ31 magnesium alloy strips using vertical twin-roll caster

A newly developed technology for manufacturing magnesium alloy strip,vertical twin-roll strip casting,has been described.This manufacturing process is easy to be facilitated in an economical way to manufacture wrought magnesium alloy strips. As an example,AZ31 magnesium alloy was used to investigate the appropriate manufacturing conditions for vertical twin-roll strip casting by varying the temperatures of the molten materials and rolling speeds.The effects of manufacturing conditions on forming quality were clarified in terms of roll speeds and casting temperature.In addition,microscopic observation and X-ray diffraction of the as-cast strips were performed.It has been determined that AZ31 alloy strip of 1-3 mm in thickness can be produced at a speed of 30 m/min by a vertical twin-roll caster.The microstructure of as-cast strip only containsα-phase(Mg)and no other phase,and the twin-roll casting process can effectively refine the grain size.The fine equiaxed grain of as-cast strips is beneficial to the plastic deformation of the strips,and it is also suitable for direct cold-rolling with a maximum cold-rolling reduction of 40%.     

Microstructure and texture evolution of AZ31 magnesium alloy during rolling

The production of magnesium alloy sheets normally involves several processing stages including hot rolling,cold rolling and intermediate annealing.The microstructure and texture evolution of AZ31 magnesium alloy sheets in different processing states were investigated by optical microscopy and X-ray diffraction technique.It is found that the microstructure of hot-rolled sheets is dominated by recrystallized equiaxed grains,while that of cold-rolled sheets is dominated by deformation twins.With final annea...     

AZ31镁合金的热挤压变形和力学性能分析

为了掌握高精度镁合金管材的生产工艺,通过对铸锭的均匀化处理,借助500 t挤压机、拉伸试验机、金相显微镜和透射电镜(TEM)对AZ31镁合金管材的等温挤压过程进行了研究,试制了AZ31镁合金挤压薄壁管材,获得了尺寸精度高、粗糙度小和壁厚差小的管材;分析了不同挤压条件下的AZ31镁合金管材的尺寸精度、组织、力学性能.研究结果表明:在挤压温度为623士20K挤出管材经523K×3h退火时其性能较好,抗拉强度、屈服强度和延伸率分别为270 MPa,175 MPa和23.1%.     

AZ31镁合金板材的冲压性能

通过对异步轧制后的AZ31镁合金板材在杯突试验机上进行冲压试验,以此来研究AZ31镁合金板材的冲压性能.采用热轧态AZ31镁合金板材在异步轧机上进行不同压下率轧制,采取空冷,然后对单道次异步轧制后的板材进行退火处理.对退火处理后的板材切块、打磨,在杯突试验机上进行冲压试验,测量板材的杯突值,通过拉伸试验测得冲压性能指标...     

基于伺服压力机的AZ31镁合金反挤压成形

为探讨挤压速度模式对AZ31镁合金杯形件反挤压成形的影响,对伺服压力机反挤压成形进行有限元分析与实验,并与普通曲柄压力机和液压机反挤压成形进行比较。有限元分析结果表明,反挤压终了阶段,伺服挤压和液压挤压最大损伤值分别为3.41和3.30,远低于普通挤压的最大损伤值6.08;挤压过程中杯形件最大温差伺服挤压为45℃,而普通挤压和液压挤压分别为127℃和70℃。实验结果表明,在1100kN伺服压力机上,采用伺服挤压模式,可成功获得壁厚为3mm的AZ31镁合金反挤压杯形件,而采用普通挤压模式,在杯形件边缘则出现破裂。实验与有限元分析结果基本吻合。     

搅拌摩擦加工AZ31镁合金的超塑性

对搅拌摩擦加工AZ31镁合金的微观组织和拉伸力学行为进行了研究。结果表明,通过搅拌摩擦加工,热轧AZ31板材的平均晶粒尺寸由92.0μm细化到11.4μm。搅拌摩擦加工板材在高温下具有优异的塑性,伸长率在温度为723K和应变速率为5×10-4s-1的条件下达到1050%。该材料还具有高应变速率超塑性,在723K和1×10-2s-1的条件下伸长率达到268%。在相同实验条件下,母材由于晶粒尺寸粗大,没有显示出超塑性。     

Texture evolution of extruded AZ31 magnesium alloy sheets

The evolution of texture during the annealing and hot rolling process of extruded AZ31 magnesium alloy sheets was studied. There are two kinds of texture components in the extruded AZ31 sheets. One is {0002}<1-010> and the other is {1-010}<1-120>. The {0002}<1-010>component predominates. After annealing at 723 K for 3 h, both {0002}<1-010> and {1-010}<1-120> components are strengthened moderately. This indicates that grains with both two components mentioned above grow faster than those with other orientations. The {1-010}<1-120> component disappears and the intensity of {0002}<1-010> component decreases significantly after hot rolling with a 30% reduction at 623 K. This is mainly attributed to rotational dynamic recrystallization (RDX) during the hot rolling.     

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。     

Tensile behaviors of fatigued AZ31 magnesium alloy

The relationship between microstructure and tensile behaviors of fatigued AZ31 magnesium alloy was investigated. Axial fatigue tests were performed on PLG–100 fatigue machine at stresses of 50 and 90 MPa. Tensile samples were cut from the fatigued samples, named as L-sample and H-sample respectively, and the O-sample was cut from original rolled AZ31 alloy. The EBSD and TEM were used to characterize the microstructure. It is found that the twinning–detwinning was the main deformation mechanism in high stress fatigue test, while dislocation slipping was dominant in low stress fatigue test. After fatigue tests, the average grain size of the L-sample and H-sample decreased to 4.71 and 5.33 μm, and the tensile and yield strength of the L-sample and H-sample increased slightly. By analyzing SEM images, the ultimate fracture region of the L-sample consisted of dimples, while there were many microvoids in the ultimate fracture region of the H-sample. Consequently, the tensile behaviors of fatigued magnesium have a close relationship with microstructure.     

挤压比对AZ31镁合金组织结构的影响

试验研究了挤压比对AZ31镁合金组织结构的影响.结果表明,258℃挤压变形镁合金在形变初期容易出现孪晶,再结晶晶粒一般出现在晶界和孪晶附近.挤压比小时动态再结晶晶粒平均尺寸为2 μm,动态结晶细化了晶粒.随着挤压比增大,晶粒尺寸减小,组织趋于均匀.挤压比达到16时,动态再结晶基本完成.挤压比为25时,能得到晶粒细小且均匀的组织,平均晶粒尺寸为7.3 μm.