Effects of Ce addition on microstructure and mechanical properties of Mg-6Zn-1Mn alloy

The effects of Ce addition on the microstructure of Mg-6Zn-1Mn alloy during casting, homogenization, hot extrusion, T4, T6 and T4＋two-step aging were investigated. The mechanical properties of alloys with and without Ce were compared. The results showed that Ce had an obvious effect on the microstructure of ZM61-0.5Ce alloy by restricting the occurrence of dynamic recrystallization and restraining the grain growth during extrusion and heat treatment subsequently. A new binary phase Mg 12 Ce was identified in ZM61-0.5Ce alloy, which distributed at grain boundaries and was broken to small particles distributed at grain boundaries along extrusion direction during extrusion. The mechanical properties of as-extruded ZM61-0.5Ce alloy were improved with the addition of Ce. The improved tensile properties of as-extruded ZM61-0.5Ce alloy were due to the finer grain sizes as compared to ZM61 alloy. However, the UTS and YS decreased severely and the elongation increased when ZM61-0.5Ce was treated by T6 and T4＋two-step aging. Brittle Mg 12 Ce phase, which was distributed at the grain boundary areas and cannot dissolve into the Mg matrix after solution treatment, became crack source under tensile stress.

Effects of ultrasonic treatment on microstructure and mechanical properties of Mg-6Zn-0.5Y-2Sn alloy

The effects of the ultrasonic treatment on the microstructure and mechanical properties of Mg-6Zn-0.5Y-2Sn alloy were investigated. The results show that the ultrasonic treatment has significant effect on the microstructure and mechanical properties of Mg-6Zn-0.5Y-2Sn alloy. The phases in Mg-6Zn-0.5Y-2Sn alloy are α-Mg, MgZn2, MgSnY, Mg2Sn, and a small amount of I-phase. With the application of ultrasonic treatment, I-phase nearly disappears, and with increasing the ultrasonic treatment power, the coarse dendrites gradually change into roundish equiaxed grains. The second phases at the α-Mg boundaries transform from coarse, semicontinuous and non-uniform to fine, discontinuous, uniform and dispersive. When the ultrasonic treatment power is 700 W, the best comprehensive mechanical properties of Mg-6Zn-0.5Y-2Sn alloy are obtained. Compared with the untreated alloy, the 0.2%tensile yield strength, ultimate tensile strength and elongation are improved by 28%, 30%and 67%, respectively.

Microstructures and mechanical properties of as-extruded and heat treated Mg-6Zn-1Mn-4Sn-1.5Nd alloy

The microstructures and mechanical properties of Mg-6Zn-1Mn-4Sn-1.5Nd alloy subjected to extrusion and T5 treatment were investigated using optical microscopy（OM）, X-ray diffractometer（XRD）, scanning electron microscopy（SEM）, electron back scattered diffraction（EBSD）, transmission electron microscopy（TEM）, hardness tests and uniaxial tensile tests. The results showed that the as-cast alloy consisted of α（Mg）, Mn, Mg7Zn3, Mg2 Sn and Mg Sn Nd phases. Dynamic recrystallization has completed during the extrusion process and the average grain size was 7.2 μm. After T5 treatment, the strength increased obviously, the yield strength and ultimate tensile strength of as-extruded alloy were increased by 94 and 34 MPa, respectively. Microstructure characterization revealed that the improvement of strength was determined by the high number density of β′1 rods.

TEM microstructure of rapidly solidified Mg-6Zn-1Y-1Ce alloy

Rapidly solidified（RS） Mg-6Zn-1Y-1Ce ribbons were prepared by single roller melt-spinning technique.Transmission electron microscopy and energy dispersive X-ray spectroscopy were employed to characterize the microstructure of RS ribbons.The results show that there is high density of particles distributed within grains and at grain boundaries in the region near wheel side.The particle density is decreased in the middle region and free surface region.The alloy is predominantly composed of supersaturated--Mg solid solution,T phase and W phase;meanwhile,a few icosahedral quasicrystalline and Mg4Zn7 particles are also observed.The T phase is confirmed having a body-centered orthorhombic structure that is transformed from the body-centered tetragonal structure Mg12Ce phase due to the partial substitution of Mg atoms by Zn.

Effect of ultrasonic melt treatment on degassing of Mg-6Zn-1Ca alloy

The effect of ultrasonic power and treatment time on degassing of Mg-6Zn-1Ca alloy was studied in this paper. The degassing effect was characterized by measuring densities of ingots. The results show that proper ultrasonic treatment can remove hydrogen from the melt of the Mg-6Zn-1Ca alloy. The ultrasonic degassing effect is closely related to the ultrasonic power density and treatment time. The degassing efficiency increases with an increase in ultrasonic power density when the melt is treated at 690 °C for 120 s, reaching its highest value at 1.2 W·cm-3. When the power density is 1.2 W·cm-3, with an increase in ultrasonic treatment time, the degassing efficiency increases at first, reaches its peak value at 120 s, then decreases as the ultrasonic treatment is further prolonged. In this experiment, the optimum degassing effect with an efficiency of 67.5 % is obtained by ultrasonic treatment with the power density of 1.2 W·cm-3 for 120 s. The maximum density of ingot can be increased from 1.8069 g·cm-3 to 1.8146 g·cm-3(increased by 0.43%).

Microstructures and properties in surface layers of Mg-6Zn-1Ca magnesium alloy laser-clad with Al-Si powders

Laser surface cladding with Al-Si powders was applied to a Mg-6Zn-1Ca magnesium alloy to improve its surface properties.The microstructure,phase components and chemical compositions of the laser-clad layer were analyzed by using X-ray diffractometry(XRD),scanning electron microscopy(SEM)and energy dispersive spectrometry(EDS).The results show that the clad layer mainly consists ofα-Mg,Mg2Si dendrites,Mg17Al12and Al3Mg2phases.Owing to the formation of Mg2Si,Mg17Al12and Al3Mg2intermetallic compounds in the melted region and grain refinement,the microhardness of the clad layer(HV0.025310)is about5times higher than that of the substrate(HV0.02554).Besides,corrosion tests in the NaCl(3.5%,mass fraction)water solution show that the corrosion potential is increased from-1574.6mV for the untreated sample to-128.7mV for the laser-clad sample,while the corrosion current density is reduced from170.1to6.7μA/cm2.These results reveal that improved corrosion resistance and increased hardness of the Mg-6Zn-1Ca alloy can be both achieved after laser cladding with Al-Si powders.

Effects of heat treatment on microstructure and mechanical properties of Mg-6Zn-4Sm-0.4Zr alloy

A new rare earth magnesium alloy(Mg-6 Zn-4 Sm-0.4 Zr, wt.%) was prepared by permanent mould casting. The microstructure and mechanical properties of the alloy sample in as-cast and various heat treatment situations were characterized with an optical microscope(OM), X-ray diffractometer(XRD), scanning electron microscope(SEM) equipped with energy dispersive spectroscope(EDS), transmission electron microscope(TEM) and mechanical tests at room temperature, respectively. The experimental results show that the as-cast alloy mainly consists of α-Mg, eutectic Mg_2Zn_3, MgZnSm and Mg_(41)Sm_5. These eutectic phases with continuous or semicontinuous morphology principally distribute along grain boundaries. Almost all the eutectic compounds dissolve in α-Mg and the grains have no obvious growth trend after optimum solution treatment at 490 °C for 18 h. Meanwhile, the ultimate tensile strength(UTS) of 229 MPa and elongation(EL) to rupture of 9.78% can be achieved through the optimal solution treatment, which increase by 37 MPa and 57.74%, respectively, compared with that of the as-cast alloy. Further aging treatments at 200 °C for different durations lead to the conspicuous increment of mechanical properties and prominent age-hardening response. Peak-aged alloy(treated at 200 °C for 12 h) reveals better mechanical properties(UTS 258 MPa, EL 9.42%, hardness 73.4 HV) compared with the same alloy treated in other aging conditions, which is mainly ascribed to precipitated Mg_2Zn_3 and MgZn_2 phases. Fracture analysis demonstrates that the as-cast alloy belongs to inter-granular and cleavage fracture patterns, while the solutionized alloy(treated at 490 °C for 18 h) reveals trans-granular and quasi-cleavage fracture modes. For the peak-aged alloy, the fracture pattern obeys the mixture of trans-granular and cleavage modes.

Corrosion and tribocorrosion behaviors of AISI 316 stainless steel and Ti6Al4V alloys in artificial seawater

The corrosion and tribocorrosion behaviors of AISI 316 stainless steel and Ti6Al4V alloys sliding against Al2O3 in artificial seawater using a pin-on-disk test rig were investigated. And the synergistic effect between corrosion and wear was emphatically evaluated. The results show that the open circuit potentials of both alloys drop down to more negative value due to friction. The corrosion current densities obtained under tribocorrosion condition are much higher than those under corrosion-only condition. Friction obviously accelerates the corrosion of the alloys. The wear loss for both alloys is larger in seawater than that in pure water. Wear loss is obviously accelerated by corrosion. And AISI 316 stainless steel is less resistant to sliding damage than Ti6Al4V alloy. The synergistic effect between wear and corrosion is a significant factor for the materials loss in tribocorrosion. In this surface-on-surface contact geometry friction system, the material loss is large but the ratio of wear-accelerated-corrosion to the total wear loss is very low.

微量Mn添加对Mg-6Zn-3Al镁合金非枝晶组织演变的影响

利用光镜(OM)、扫描电镜(SEM)、X射线衍射仪(XRD)研究了Mg-6Zn-3Al-xMn(x%=0%,0.1%,0.3%,0.5%,质量分数)合金的铸态组织和在等温热处理过程中的非枝晶组织演变规律。结果表明:铸态基体合金由α-Mg、Mg_2Zn_3、Mg_7Zn_3和Mg_(32)(Al,Zn)_(49))相组成。添加Mn后,析出了Al Mn和Al_8Mn_5相,且随Mn含量的增加,晶粒逐渐得到细化。合金经580℃等温保温30 min后,获得的非枝晶组织由初生α_1-Mg颗粒和包裹在共晶组织中二次水淬凝固形成的α_2-Mg颗粒及分布在初生颗粒间呈蜂窝状的共晶相组成。随着Mn含量增加,固相颗粒的平均尺寸和形状因子呈先减小后增加的趋势,组织中液相比例逐渐减少。当Mn含量(质量分数)为0.1%时,可获得近似球状、细小圆整、均匀分布的固相颗粒。在等温热处理过程中,溶质扩散和界面张力对组织演变起主导作用。Zn和Al溶质原子在液相中的成分起伏是初生颗粒在分离和球化过程中产生颈缩的重要原因。

热处理工艺对Mg-6Zn-3Al镁合金显微组织和力学性能的影响

通过金属型铸造制备新型Mg-6Zn-3Al(ZA63,质量分数,%)镁合金,并利用光镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)和力学性能测试研究ZA63合金在铸态、固溶和时效处理后显微组织和力学性能的变化规律。结果表明:合金铸态组织主要由基体α-Mg、晶界处呈连续或半连续分布的(α-Mg+Mg_2Zn_3+Mg_7Zn_3+Mg_(32)(Al,Zn)_(49))共晶和晶内孤立的颗粒相组成。合金在350℃固溶12～36 h时,随着时间延长,固溶效果逐渐增强,且在28 h时获得了较好的组织和241 MPa的抗拉强度及11.12%的伸长率。随后在180℃时效6～72 h后,合金的抗拉强度进一步提高,力学性能随保温时间延长呈先增加后减小的趋势,其中时效24 h时同时出现抗拉强度、伸长率和硬度的峰值298 MPa、9.78%和96.3 HV,比铸态的214 MPa、8.54%、62.2 HV分别提高39.25%、14.52%和54.82%。180℃时效24 h后,析出相的主要形态有板条状和短棒状。

Deformed microstructure and texture of Ti6Al4V alloy

Microstructure and texture evolution during hot compression of Ti6Al4 V alloy with an initial equiaxed microstructure were studied in the temperature range of 850-930 °C, strain rate range of 0.01-1 s-1 and engineering compressive strain of 70%. The results indicate that when temperature is below 900 °C and strain rate is higher than 0.1 s-1, the microstructure is mainly composed of elongated α grains. While deforming at higher temperatures and lower strain rates, dynamic recrystallization takes place. Electron back scattered diffraction（EBSD） result shows that during dynamic recrystallization, subgrain boundaries absorb dislocations and the recrystallized grains with high angle grain boundary form. At 930 °C dynamic recrystallization has basically completed, and needlelike α phase forms after water quenching. Pole figure analysis indicates that compared with the initial specimen, textures below 930 °C are weaker, while at 930 °C they are stronger.

Microstructure of Mg-8Zn-4Al-1Ca aged alloy

The microstructure of Mg-8Zn-4Al-1Ca aged alloy was investigated by TEM and HRTEM. The results show that the hardening produced in the Mg-8Zn-4Al-1Ca alloy is considerably higher than that in the Mg-8Zn-4A1 alloy. A dense dispersion of disc-like Ca2Mg6Zn3 precipitates are formed in Mg-8Zn-4Al-1Ca alloy aged at 160 ℃ for 16 h. In addition, the lattice distortions, honeycomb-looking Moir＆#233; fringes, edge dislocations and dislocation loop also exist in the microstructure. The precipitates of alloy aged at 160 ℃ for 48 h are coarse disc-like and fine dispersed grainy. When the alloy is subjected to aging at 160 ℃ for 227 h, the microstructure consists of numerous MgZn2 precipitates and Ca2Mg6Zn3 precipitates. All the analyses show that Ca is a particularly effective trace addition in improving the age-hardening and postponing the formation of MgZn2 precipitates in Mg-8Zn-4Al alloy aged at 160 ℃.

Sn对Mg-6Zn-3Al合金微观组织和力学性能的影响

利用光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)、室温拉伸试验等研究了Sn含量对Mg-6Zn-3Al-xSn(x=0,2,4 mass%)合金组织与性能的影响。结果表明:铸态合金主要由α-Mg、MgAlZn以及Mg2Sn相组成,且均呈枝晶结构。Mg2Sn相随着Sn的添加逐渐出现,第二相逐渐聚集生长为网状结构。随着Sn含量的增加,挤压态合金的晶粒逐渐细化、尺寸变均匀。挤压态Mg-6Zn-3Al-4Sn合金拥有最佳的力学性能:抗拉强度、屈服强度、伸长率分别为328 MPa、244 MPa、21.2%。该合金经双级时效(75℃预时效24 h+150℃时效18 h)工艺处理后,屈服强度提高到288 MPa,伸长率降为16.4%。

Wear behavior of Ti6Al4V biomedical alloys processed by selective laser melting, hot pressing and conventional casting

The aim of this work was to study the influence of the processing route on the microstructural constituents,hardness andtribological(wear and friction)behavior of Ti6Al4V biomedical alloy.In this sense,three different processing routes were studied:conventional casting,hot pressing and selective laser melting.A comprehensive metallurgical,mechanical and tribologicalcharacterization was performed by X-ray diffraction analysis,Vickers hardness tests and reciprocating ball-on-plate wear tests ofTi6Al4V/Al2O3sliding pairs.The results showed a great influence of the processing route on the microstructural constituents andconsequent differences on hardness and wear performance.The highest hardness and wear resistance were obtained for Ti6Al4Valloy produced by selective laser melting,due to a markedly different cooling rate that leads to significantly different microstructurewhen compared to hot pressing and casting.This study assesses and confirms that selective laser melting is potential to producecustomized Ti6Al4V implants with improved wear performance.

Microstructure and mechanical properties of Ti6Al4V alloy prepared by selective laser melting combined with precision forging

To improve the mechanical properties of Ti6Al4V alloy prepared by selective laser melting(SLM)process,the precision forging was conducted at950°C and different strains and strain rates.The microstructure evolution of as-built samples and forged samples in both horizontal and vertical sections was visualized and analyzed by optical microscope and X-ray diffraction.The microstructure was improved by the precision forging and subsequent water quenching.The porosity in each section was accounted.It can be seen that high strain rate and large deformation result in low porosity,consequently contributing to a better fatigue performance.The micro-hardness was lowered after precision forging and water quenching,while the difference of microhardness between the horizontal and vertical sections became smaller,which illustrated that this process can improve the anisotropy of structural components fabricated by SLM.

Tribological behavior of different films on Ti-6Al-4V alloy prepared by plasma-based ion implantation

The tribological behaviors of TiN coating and TiN+TiC+Ti(C, N)/diamond like carbon (DLC), TiN/DLC, TiC/DLC multilayers on Ti 6Al 4V alloy prepared by plasma based ion implantation (PBII) were compared. Under the test conditions of counterbody AISI 52100, load 1 N and speed 0.05 m/s, the tribological properties of the alloy are improved by these films in the order of TiN, TiC/DLC, TiN/DLC and TiN+TiC+Ti(C,N)/DLC. Tribological behavior is affected by the conditions of surface modification and triboexperiments. The appearance of “peaks” in the wear dynamic resistance profiles may be due or correspond to the process of formation and breaking apart of transition films. The breakthrough of the DLC coated samples may start from partially wearing out, and end with joining piece dilamination. There are transition films on all counterbodies AISI 52100. When AISI 52100 counterbody is changed to Ti 6Al 4V, the wear of most modified samples is changed from only disc to both disc and ball abrasive dominated.

Effects of RE on the Microstructure of Mg-8Zn-4Al Magnesium Alloys

The effects of RE on the microstrcture of as-cast Mg-8Zn-4Al magnesium alloys were investigated. The results show that the solidification range of Mg-8Zn-4Al-xRE alloys increases with RE additions. A binary eutectic reaction can arise and produce a new phase （Mg：Al：Zn：RE） and the temperature of phase transformation point of the new phase is 412.85 C. In Mg-8Zn-4Al-1.5RE alloy, a small amount of Mg：Al：Zn：RE phase and ε phases are found besides a（Mg）,φand r phases. Also microstructures of Mg-8Zn-4Al alloys can be refined by addition of 1.5% RE obviously.

Growth process and corrosion resistance of micro-arc oxidation coating on Mg-Zn-Gd magnesium alloys

A Mg-6Zn-3Gd(mass fraction,%) alloy,noted as ZG63,was coated by different micro-arc oxidation(MAO) processes,and the coating structure and corrosion resistance of the alloy were studied using scanning electron microscopy(SEM),glancing angle X-ray diffractometry(GAXRD) and various electrochemical methods.The micro-arc oxidation process consists of three stages and corresponds with different coating structures.In the initial stage,the coating thickness is linearly increased and is controlled by electrochemical polarization.In the second stage,the coating grows mainly inward and accords with parabolic regularity.In the third stage,the loose coating forms and is controlled by local arc light.The looser coating is mainly composed of MgSiO3 and the compact coating is mainly composed of MgO.From micro-arc oxidation stage to local arc light stage,the corrosion resistance of the coated alloy firstly increases and then decreases.The satisfied corrosion resistance corresponds to the coating time ranging from 6 to10 min.

Microstructure and electrochemical corrosion behavior of selective laser melted Ti−6Al−4V alloy in simulated artificial saliva

Ti−6Al−4V alloy was fabricated via selective laser melting(SLM)to improve its corrosion resistance for implant.The microstructure and electrochemical corrosion behavior were investigated using scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),electrochemical test and contact angle test.It can be found that the as-selective laser melted(as-SLMed)Ti−6Al−4V alloys showβcolumnar microstructure in building direction and nearly circular checkerboard microstructure in scanning direction,while the wrought and wrought+HT samples exhibit equiaxed microstructure.The as-SLMed Ti−6Al−4V alloy exhibits better corrosion resistance than the wrought and wrought+HT samples due to hydrophobicity,high grain boundary density and uniform distribution of alloying elements in simulated artificial saliva at 37℃.

Preparation of micro/nano-structured ceramic coatings on Ti6Al4V alloy by plasma electrolytic oxidation process

In order to improve the osseointegration and antibacterial activity of titanium alloys,micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation(PEO)process on Ti6Al4V alloy in NaF electrolyte.The influence of NaF concentration(0.15-0.50 mol/L)on the PEO process,microstructure,phase composition,corrosion resistance and thickness of the coatings was investigated using scanning/transmission electron microscopy,energy dispersive spectroscopy,atomic force microscopy,X-ray diffractometer,and potentiodynamic polarization.The results demonstrated that Ti6Al4V alloy had low PEO voltage(less than 200 V)in NaF electrolyte,which decreased further as the NaF concentration increased.A micro/nano-structured coating with 10-15μm pits and 200-800 nm pores was formed in NaF electrolyte;the morphology was different from the typical pancake structure obtained with other electrolytes.The coating formed in NaF electrolyte had low surface roughness and was thin(<4μm).The NaF concentration had a small effect on the phase transition from metastable anatase phase to stable rutile phase,but greatly affected the corrosion resistance.In general,as the NaF concentration increased,the surface roughness,phase(anatase and rutile)contents,corrosion resistance,and thickness of the coating first increased and then decreased,reaching the maximum values at 0.25 mol/L NaF.