Dry sliding wear behavior of as-cast ZE41A magnesium alloy

In present work, an attempt has been made to investigate the wear behavior of as-cast ZE41A magnesium alloy during dry sliding. The experiments were performed using pin-on-disc type wear apparatus against a EN32 steel counterface in a load range of 30–150 N, sliding velocity range of 0.5–2.5 m/s and at a constant sliding distance of 1500 m. Microstructural investigations on the worn surfaces were undertaken using a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) for determination of type of damage and nature of distortion at the surface. Wear mechanisms such as abrasion, oxidation, delamination, plastic deformation and melting were identified. Wear maps were drawn for the test result data. Mild wear, severe wear and ultra severe wear regimes were identified using wear transition map through microstructural observations.     

Calorimetric analysis of AZ91D magnesium alloy

In order to study the activation energies and microstructure evolution of β-Mg₁₇Al₁₂ and eutectic structure in AZ91D magnesium alloy, calorimetric analyses were carried out using non-isothermal measurements by DSC and scanning electron microscopy (SEM) with EDX. During DSC tests, two peak temperatures of β-Mg₁₇Al₁₂ dissolution/precipitation and eutectic transformation were delayed in the heating/cooling process with the increase of scanning rates due to the occurrence of superheating/supercooling. Activation energies of β-Mg₁₇Al₁₂ dissolution and eutectic transformation were derived using multiple heating rates. Furthermore, the results of SEM and EDX revealed that the size and morphology of eutectic structures in the alloy had a close relationship with the time of β-Mg₁₇Al₁₂ phase dissolution during the heating process. More eutectic structures formed at low scanning rate due to sufficient time for the diffusion of Al in α-Mg regions.     

Improving the wear resistance of AZ91D magnesium alloys by laser cladding with Al-Si powders

To improve the wear resistance of AZ91D magnesium alloy, laser surface cladding with Al and Si powders was investigated using a Nd:YAG pulsed laser. With appropriate processing parameters and the suitable weight ratio of Al to Si in powders, a modified surface layer free of cracks and pores was formed by reaction synthesis of Mg with Al and Si. X-ray diffractometry (XRD) confirmed the main phases in the layer to be Mg₂Si and Mg₁₇Al₁₂. The surface hardness increased from 35 HV for as-received magnesium alloy to more than 170 HV for laser treated sample. Accompanying the increase in hardness, the wear resistance of the clad layer increased more than 4 times that of the substrate.     

Microstructural evolution in AZ91D magnesium alloy during electron beam welding

Vacuum electron beam welding can have a low heat input, which means there is a minimum heat affected zone during welding of AZ91D magnesium alloy. From the observed microstructure, the weld of the AZ91D magnesium alloy can be divided into four regions, which are the weld metal zone, a partially-melted zone adjacent to the fusion boundary, a partially-melted zone adjacent to the base metal and the base metal zone. A sharp transition from the fusion zone to the non-melted zone, especially the characteristic partial melting microstructure and nature of the alloy elements, was observed. It was found that significant partial melting had taken place in the very narrow region around the weld metal of the AZ91D magnesium alloy. The Al content of eutectic β-Mg₁₇Al₁₂ in the partially-melted zone adjacent to the fusion boundary was close to the content in the continuously precipitated eutectic β particles in the fusion zone and much lower than the eutectic β in the base metal. The fully melted eutectic β-phase coexisted with the partially melted eutectic β phase in the partially-melted zone adjacent to the base metal.     

Cu-Cr-Zr合金电滑动磨损行为研究

将经过480℃×2h时效处理和拉拔成型制得的Cu-0.40Cr-0.10Zr合金线材在自制电磨损试验机上进行电滑动磨损实验,并运用扫描电子显微镜、能谱分析等方法对Cu-Cr-Zr合金滑动磨损表面形貌及电磨损机理进行了观察和分析.结果表明,在不加载电流的情况下Cu-Cr-Zr合金的滑动磨损机制为粘着磨损和磨粒磨损;在载流条件下的磨损机制为粘着磨损、磨粒磨损以及电烧蚀磨损,并且随着电流强度的增大,粘着磨损和电烧蚀磨损的程度也越严重.     

Metadynamic recrystallization behavior of AZ61 magnesium alloy

Metadynamic recrystallization (MDRX) behavior of AZ61 magnesium alloy and its effects on flow behavior and microstructure evolution have been investigated in this study. Towards this end, a set of double-hit hot compression tests was conducted under strain rate of 0.1 s⁻¹ at 400 °C. To differentiate the static and metadynamic recrystallization dominant strain regions, the first stage of deformation was carried out up to the different pre-strains with a constant inter-pass annealing time of 200 s. The results indicated that the MDRX is predominant recrystallization mechanism where the pre-strains are higher than 0.35. Furthermore, to investigate the influence of MDRX on subsequent flow behavior and the related microstructure, an elaborated inter-pass annealing treatment was executed employing a range of inter-pass annealing time (2–500 s). The results show that the progress of MDRX leads to an increase in the flow stress as well as the rate of work hardening encountered in the subsequent deformation. Additionally, the microstructural examinations confirm that the observed hardening phenomenon is a consequence of grain growth evolved from MDRX and its direct effect on the onset of dynamic recrystallization at the second stage of deformation.     

Effect of deep cryogenic treatment on microstructure, creep and wear behaviors of AZ91 magnesium alloy

This paper focuses on the effect of deep cryogenic treatment (−196 °C) on microstructure and mechanical properties of AZ91 magnesium alloy. The execution of deep cryogenic treatment on samples changed the distribution of β precipitates. The tiny laminar β particles almost dissolved in the microstructure and the coarse divorced eutectic β phase penetrated into the matrix. This microstructural modification resulted in a significant improvement on mechanical properties of the alloy. The steady state creep rates were measured and it was found that the creep behavior of the alloy, which is dependent on the stability of the near grain boundary microstructure, was improved by the deep cryogenic treatment. For the AZ91 alloy, the results indicate a mixed mode of creep behavior, with some grain boundary effects contributing to the overall behavior. However for the deep cryogenic samples dislocation climb controlled creep is the dominant deformation mechanism. After the deep cryogenic treatment the sliding of grain boundaries was greatly suppressed due to morphological changes. As a result, the grain boundaries are less susceptible for grain boundary sliding at high temperatures. Dry sliding wear tests were also applied and the wear resistance of the alloy improved remarkably after deep cryogenic treatment.     

AZ91D镁合金阳极氧化与热扩散渗铝复合膜层的研究

将阳极氧化与热扩散相结合对AZ91D镁合金表面进行低温渗铝处理,利用扫描电镜、光学显微镜和X射线衍射仪对所得膜层的形貌、相结构及耐腐蚀性能进行了研究,并对复合膜层改善镁合金基体耐腐蚀性能的过程进行了分析.研究表明,该复合膜层是由MgO和金属间化合物Mg17Al12以及被γ相(Mg17Al12)包裹住的α-Mg晶粒共同组成;AZ91D镁合金表面的阳极氧化和热扩散渗铝复合膜层能显著提高镁合金基体材料的耐腐蚀性能.     

变形的AZ91D镁合金半固态等温压缩的力学行为

为了了解等径道角挤压(ECAE)的AZ91D镁合金在半固态压缩变形中的力学特征,利用半固态温压缩实验、Gleeble1500实验机和金相显微镜对其在半固态压缩变形中的力学行为进行了研究.结果表明:ECAE的AZ91D镁合金在半固态等温压缩中变形由固相晶粒本身的塑性变形、液相包围着固相晶粒的滑动和转动构成;该材料的真应力-真应变曲线由应力激增阶段、应力下降阶段、稳态阶段和应力增加阶段组成;随保温时间的增加或变形温度的升高,获得相同应变量的真应力明显下降,稳态应力和峰值应力也明显下降;随应变速率的增加,稳态应力增加.     

Development of ternary Mg based alloy for soldering of AZ31B magnesium alloy

Abstract

Two kinds of ternary Mg based alloys were designed to join the AZ31B magnesium alloy plates by high frequency induction soldering with argon shielding gas. The microstructures and properties of the filler metals and joints were investigated by SEM, X-ray diffraction, differential scanning calorimetry, spreading test and tensile test. The results have shown that the microstructures of Mg–31·5Al–10Sn filler metal mainly consist of Mg₁₇Al₁₂, Mg₂Sn and a trace amount of α-Mg phases, while the microstructures of Mg–29·5Zn–1Sn filler metal include α-Mg phase and Mg₇Zn₃ with a trace of α-Mg and Mg₂Sn phases. Both of the filler metals have narrow melting zones; however, the spreading area of the Mg–31·5Al–10Sn filler metal is much larger than that of the Mg–29·5Zn–1Sn filler metal on the AZ31B base metal. The average tensile strength of solder joints with Mg–31·5Al–10Sn filler metal is a little higher than that of the latter solder joints with Mg–29·5Zn–1Sn filler metal.     

Machining characteristics,wear and corrosion behavior of AZ91 magnesium alloy - fly ash composites produced by friction stir processing

In the present work, fine grained AZ91 magnesium alloy – fly ash composite has been successfully fabricated by friction stir processing. Microhardness measurements show marginally higher hardness with uniform distribution compared with the base material. No significant difference in the mean cutting force was observed during drilling of the base metal and the composite. However, lower cutting forces were recorded in the sub-surface region of the composites. Interestingly, decreased corrosion resistance was noticed for the composite compared with the base material. Lower mass loss has been observed for the composite during reciprocating wear experiments. The results strongly suggest that the surface composite of AZ91 magnesium alloy – fly ash exhibits better mechanical and wear properties. However, decreased corrosion resistance is a significant observation that warns the applicability of these composites in corroding environment.     

Wear coefficient and reliability of sliding wear test procedure for high strength aluminium alloy and composite

This paper describes the results of dry sliding wear tests of aluminium alloy (Al–Zn–Mg–Cu) composite was examined under varying applied pressures (0.2–2.6 MPa) and sliding speeds of 0.52, 1.72, 3.35, 4.18 and 5.23 m/s. The wear behaviour was studied using pin-on-disc apparatus against heat-treated steel counter surface, giving emphasis on the parameters such as wear coefficient as a function of applied pressure for alloy and composite for various sliding velocities. Wear coefficient of the alloy was noted to be significantly higher than that of the composite and is suppressed further due to addition of silicon carbide particles and applied pressure. It is noted that the experimental values are in good agreement with the theoretically calculated value. The maximum deviation of experimental values from the theoretical ones is noted to be around 10–15%. This supports the reliability of the test procedures and reproducibility of the test data.     

The effect of PVD coatings on the corrosion behaviour of AZ91 magnesium alloy

In this study, multilayered AlN (AlN + AlN + AlN) and AlN + TiN were coated on AZ91 magnesium alloy using physical vapour deposition (PVD) technique of DC magnetron sputtering, and the influence of the coatings on the corrosion behaviour of the AZ91 alloy was examined. A PVD system for coating processes, a potentiostat for electrochemical corrosion tests, X-ray difractometer for compositional analysis of the coatings, and scanning electron microscopy for surface examinations were used. It was determined that PVD coatings deposited on AZ91 magnesium alloy increased the corrosion resistance of the alloy, and AlN + AlN + AlN coating increased the corrosion resistance much more than AlN + TiN coating. However, it was observed that, in the coating layers, small structural defects e.g., pores, pinholes, cracks that could arise from the coating process or substrate and get the ability of protection from corrosion worsened were present.     

Damping behaviour of AZ91 magnesium alloy with cracks

The amplitude-dependent damping of a commercial magnesium cast alloy AZ91 was determined at room temperature by measurement of the logarithmic decrement of free decaying vibrations of bending beams clamped at one side. In order to generate cracks in the specimens they were subjected to (1) isochronal heat treatments for 1 h at temperatures above 400 °C with succeeding quenching in cold water and (2) controlled fatigue bending loading in the same equipment also used for the damping measurements. After both treatments, the amplitude-dependent damping curves show a maximum for strains 10⁻⁵ to 10⁻³, which can be correlated with the presence of cracks and can be explained by a simple rheological model based on crack damping. This maximum is enhanced when the number of loading cycles or the quenching temperature is increased which can be explained by crack nucleation. Crack growth with increasing number of loading cycles shifts the maximum to lower strains.     

半固态AZ91D镁合金的压缩变形和显微组织

利用平行板触变压缩仪研究了电磁搅拌的半固态AZ91D合金试样的压缩变形和组织.结果表明:随着半固态压缩变形温度的升高,AZ91D镁合金试样变形的速度加快,即变形应变速度增大,但压缩应力不断下降;在某一载荷下,AZ91D镁合金试样压缩变形应力和应变呈明显的线性关系,与压缩温度的高低无关.随着半固态压缩载荷的提高,AZ91D镁合金试样变形的速度增加,应变速度增大,应力下降速度加快;在不同的压缩载荷下,AZ91D镁合金试样的压缩变形应力和应变都呈明显的线性关系.在实验中的各种半固态压缩变形条件下,初生α-Mg在压缩后AZ91D镁合金试样组织中的分布很均匀,几乎不存在组织偏析.当初生固相的形态呈球状结构,在相同的变形条件下,不同种类合金的半固态压缩变形规律非常相似.     

The surface chemistry of 3-mercaptopropyltrimethoxysilane films deposited on magnesium alloy AZ91

Magnesium and its alloys have desirable physical and mechanical properties for a number of applications. Unfortunately, these materials are highly susceptible to corrosion, particularly in the presence of aqueous solutions. The purpose of this study is to develop a uniform, non-toxic surface treatment to enhance the corrosion resistance of magnesium alloys. This paper reports the influence of the coating bath parameters and alloy microstructure on the deposition of 3-mercaptopropyltrimethoxysilane (MPTS) coatings on magnesium alloy AZ91. The surface chemistry at the magnesium/MPTS interface has also been explored. The results indicate that the deposition of MPTS onto AZ91 was influenced by both the pH and MPTS concentration in the coating bath. Furthermore, scanning electron microscopy results showed that the MPTS film deposited uniformly on all phases of the magnesium alloy surface. X-ray photoelectron spectroscopy studies revealed that at the magnesium/MPTS interface, the molecules bond to the surface through the thiol group in an acid-base interaction with the Mg(OH)₂ layer, whereas in the bulk of the film, the molecules are randomly oriented.     

Corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions

The corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions was studied using electrochemical measurements, whereby a corrosion map in terms of electrode potential and chloride concentration [Cl⁻] was obtained. AZ91 alloy exhibited the corrosion and passivation zones in dilute NaCl solutions. The passivation zone became narrow with increasing [Cl⁻]. The values of open-circuit potential were in the passivation zone when the [Cl⁻] was less than 0.5 mol/L. XRD patterns showed the presence of the Mg(OH)₂, Mg₅(CO₃)₄(OH)₂·8H₂O and MgO phases in the corrosion product, whereas the latter two phases found in the passive film.     

Characterization of the fatigue behaviour of the magnesium alloy AZ91D by means of mechanical hysteresis and temperature measurements

Stress-controlled load increase and constant amplitude tests were performed on the cast magnesium alloy AZ91D. Rather small values of the plastic strain amplitude reflect the very localised plastic deformation predominant in the _I-phase. The cyclic deformation and temperature curves of the load increase tests exhibit cyclic yield strength values which allow a good estimation of the endurance limit. Stress amplitudes above the endurance limit lead to cyclic hardening. As compared to the behaviour under monotonic tensile loading, the alloy exhibits cyclic hardening. Microscopic investigations illustrate the different influences of the - and β-phase in respect to crack initiation.     

Influence of focusing thermal effect upon AZ91D magnesium alloy weld during vacuum electron beam welding

The influence of focusing thermal effect upon the weld shape, microstructure and alloying elements distribution in the welded joints during vacuum electron beam welding on AZ91D magnesium alloy was studied. The results show that the focus state affects the offset of DOF, and further significantly affects the actual welding heat input in the process of vacuum electron beam welding. The sharp focusing state is characterized with higher welding energy density, but the welding energy density of defocusing state is lower. Therefore, the welding process with sharp focusing state and smaller calculation welding heat input can obtain the same weld penetration as the welding process is the conditions of defocusing state and larger calculation welding heat input. And the welding process of sharp focusing state and smaller calculation welding heat input can induce more strongly burning loss of Mg element than the conditions of defocusing state and larger calculation welding heat input. Then, which will affect the distribution of alloy elements in weld seam.