Compressive Deformation of Semi-Solid AZ91D Magnesium Alloy

The compression tests of semi-solid AZ91D Mg alloy have been conducted on a parallel-plate viscometer. The results are as follows. With increasing the compression temperature, the deformation rate or the strain rate of the specimens rises, but the compressive stress continuously decreases; the deformation strain is obviously linear with the compressive stress and independent on compression temperature under a given compression load. In the wake of the compression load being added, the compressive strain increases but the compressive stress decreases clearly; the deformation strain is obviously linear with the compressive stress under different compression load. The mathematical apparent viscosity model about the semi-solid compressed AZ91D Mg alloy has been established, i.e. ηapp=2004.2exp(15.61fs)γ1.317fs-1.3511.     

消失模铸造AZ91镁合金的研究

研究了ZA91镁合金消失模铸造时铸件的厚度,位置和真空度对铸件质量,组织及力学性能的影响,真空度是决定铸件质量的一个关键的工艺因素,无真空时浇注铸件易产生浇不足缺陷,但真空度过大又会导致形成粘砂和气孔等缺陷,真空浇注射明显细化组织,但真空度进一步增大时细化效果野 不明显,铸件显微组织具有很大的壁厚效应,然 位置对组织的影响与是否采用抽真空措施有关,铸件壁厚较小时,铸件的力学性能总体较差,断裂源自Mg/Mg17Al12界面、且主要是以解决理形式的脆性断裂。     

Mcchanical and Microstructural Properties of Ultra-fine Grained AZ91 Magnesium Alloy l ubes Processed via Multi Pass Tubular Channel Angular Pressing (TCAP)

Ultra-fine grained(UFG) cylindrical tubes were produced via recently developed tubular channel angular pressing(TCAP) process through different passes from as-cast AZ91 magnesium alloy.The microstructure and mechanical properties of processed tube through one to four passes of TCAP process at 200 ℃ were investigated.Microhardness of the processed tube was increased to 98.5 HV after one pass from an initial value of 67 HV.An increase in the number of passes from one to higher number of passes has no more effect on the microhardness.Yield and ultimate strengths were increased by 4.3 and 1.4 times compared to those in as-cast condition.Notable increase in the strength was achieved after one pass of TCAP while higher number of passes has no more effect.Microstructural investigation shows notable decrease in the grain size to around 500 nm from the primary value of ~ 150 μm.Dissolution and distribution of hard Mg_(17)Al_(12) phase in the grain boundaries of dynamically recrystallized UFG AZ91 with a mean grain size of ~500 nm was an interesting issue of TCAP processing at 200 ℃ compared to other severe plastic deformation processes.     

等通道角变形对搅拌铸造SiC_P/AZ91复合材料显微组织与室温性能的影响

采用搅拌铸造法成功制备了SiC_P/Mg(AZ91)复合材料并对铸态复合材料进行了等通道角挤压变形(Equal channel angular pressing,ECAP)。结果表明,搅拌铸造态SiC_P/AZ91复合材料的基体组织致密,颗粒与基体结合良好,没有出现宏观团聚;SiC_P大部分聚集在晶界附近区域并呈"项链状"分布。ECAP变形可以有效地消除铸态SiC_P/AZ91复合材料中的SiC_P"项链状"分布,并且随着ECAP道次的增加,SiC_P分布更加均匀;在ECAP过程中,SiC_P发生了一定断裂但并不明显。SiC_P/AZ91复合材料基体晶粒随着变形道次的提高而逐渐细化。基体晶粒细化以及SiC_P分布均匀化是SiC_P/AZ91复合材料屈服强度和抗拉强度随着道次提升而逐渐增加的主要原因。     

An investigation on the tribological behavior of AZ91 and AZ91 + 3 wt% RE magnesium alloys at elevated temperatures

The wear behavior of AZ91 and AZ91 + 3 wt% RE magnesium alloys was investigated under a normal load of 20 N at the wear testing temperatures of 25–250 °C and sliding speeds of 0.4 and 1 m s⁻¹. As the sliding speed increased from 0.4 to 1 m s⁻¹ at the wear temperature of 25 °C, the wear rates of AZ91 and AZ91 + 3 wt% RE alloys decreased by about 8% and 60%, respectively. With an increase in the wear temperature to 100 °C, the wear rate of AZ91 alloy was reduced by 58% at a sliding speed of 0.4 m s⁻¹, while the wear rate was sharply increased at a sliding speed of 1 m s⁻¹. At higher wear temperatures, the wear of the AZ91 alloy at both sliding speeds soared as a result of the softening of β-Mg₁₇Al₁₂ phase. However, the wear rate of AZ91 + 3 wt% RE alloy showed a minimum at the wear temperatures of 100 and 200 °C at sliding speeds of 1 and 0.4 m s⁻¹, respectively. Superior wear behavior of AZ91 + 3 wt% RE at the elevated temperatures could be attributed to its higher thermal stability and strength. Furthermore, a rise in sliding speed led to a 55% reduction in the wear rate of AZ91 + 3 wt% RE alloy at the wear temperature of 100 °C due to the formation of stable oxide layers on the wear surface.     

Surface characterization and cytocompatibility evaluation of silanized magnesium alloy AZ91 for biomedical applications

Mg alloys with high Al contents have superior corrosion resistance in aqueous environments, but poor cytocompatibility compared to that of pure Mg. We have silanized the cast AZ91 alloy to improve its cytocompatibility using five different silanes: ethyltriethoxysilane (S1), 3-aminopropyltriethoxysilane (S2), 3-isocyanatopyltriethoxysilane (S3), phenyltriethoxysilane (S4) and octadecyltriethoxysilane (S5). The surface hydrophilicity/hydrophobicity was evaluated by water contact angle measurements. X-ray photoelectron analysis was performed to investigate the changes in surface states and chemical composition. All silane reagents increased adsorption of the albumin to the modified surface. In vitro cytocompatibility evaluation revealed that silanization improved cell growth on AZ91 modified by silane S1. Measurement of the concentration of Mg²⁺ ions released during the cell culture indicated that silanization does not affect substrate degradation.     

Surface characterization and cytocompatibility evaluation of silanized magnesium alloy AZ91 for biomedical applications

Abstract

Mg alloys with high Al contents have superior corrosion resistance in aqueous environments, but poor cytocompatibility compared to that of pure Mg. We have silanized the cast AZ91 alloy to improve its cytocompatibility using five different silanes: ethyltriethoxysilane (S1), 3-aminopropyltriethoxysilane (S2), 3-isocyanatopyltriethoxysilane (S3), phenyltriethoxysilane (S4) and octadecyltriethoxysilane (S5). The surface hydrophilicity/hydrophobicity was evaluated by water contact angle measurements. X-ray photoelectron analysis was performed to investigate the changes in surface states and chemical composition. All silane reagents increased adsorption of the albumin to the modified surface. In vitro cytocompatibility evaluation revealed that silanization improved cell growth on AZ91 modified by silane S1. Measurement of the concentration of Mg²⁺ ions released during the cell culture indicated that silanization does not affect substrate degradation.     

Ion implantation effect on atomic structure of deformed Si, Ir, W, Ni and Cu

It has been revealed, that in Ir subjected to severe plastic deformation, an ultrafine grained structure (UFG) is formed (the grain size of 20-30 nm). Practically no defects have been detected within the grains, while, in the case of Ar⁺ implantation, the subgrain structure with characteristic sizes of about 3-5 nm is formed; defects have been detected within subgrains.The subgrain structure was also revealed in UFG Ni and Cu after severe plastic deformation (SPD) (subgrain size of 3-15 nm), but in the latter case the observed boundary region is broader and subgrain is highly disoriented.     

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.     

AZ91D镁合金化学镀Ni-P/Ni-W-P双层镀层研究

为了提高镁合金的耐磨耐蚀性,研究了一种镁合金直接化学镀Ni-P/Ni-W-P双层镀层的方法.采用扫描电镜(SEM)和X-射线衍分析射仪(XRD)分析了镀层的微观结构.对镀层进行了极化曲线分析,并进行了盐酸腐蚀试验和结合力试验.结果表明,该复合镀层组织致密无孔,具有较高的显微硬度和高耐蚀性.镀层硬度可达622HKV,试样在10%的HCl溶液中可保持近3h不腐蚀基体,对镁合金起到很好的保护作用.     

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.     

AZ91D镁合金托弹板半固态触变模锻研究

为了掌握半固态触变模锻中工艺参数对成形零件的微观组织和力学性能的影响规律,借助拉伸试验机和金相显微镜对AZ91D镁合金托弹板的半固态触变模锻过程进行了研究.AZ91D镁合金半固态坯料分别采用传统SIMA法和新SIMA法制备.结果表明:压力对托弹板零件的充型过程有很大影响,当压力为500 kN,托弹板零件充型不满;当压力为2000 kN,托弹板零件充型良好.坯料加热温度和保温时间对托弹板零件的力学性能有一定影响.当压力为2000 kN,模具预热温度为450 ℃,坯料在545 ℃保温20 min时,新SIMA法制备的半固态坯半固态触变模锻成形的托弹板零件获得最佳的力学性能.与传统SIMA法相比,新SIMA法制备的半固态坯成形的托弹板零件的室温力学性能和100℃的高温力学性有很大提高.     

挤压对AZ91铸造镁合金力学性能的影响

对挤压变形前后的AZ91镁合金进行了微观组织和力学性能研究.结果表明:挤压成形后合金的抗拉强度和塑性均得到提高;孪晶的产生,导致挤压合金室温压缩的应力-应变曲线上有屈服平台出现;晶粒尺寸强烈影响合金的强度.室温时,挤压合金的流变强度较铸态的高,而高温压缩的强度则较铸态的低.     

Simulation and experimental investigation of FSP of AZ91 magnesium alloy

A thermo-mechanical simulation of the friction stir processing (FSP), using the DEFORM 3D software based on Lagrangian implicit, was developed and verified by the experimental results. Simulation can successfully predict the temperature and effective strain distributions. Material flow around the tool pin was examined using the point tracking. It was found that the major part of material flow occurs at the advancing side, and consequently, stirred zone (SZ) stretches toward the advancing side. However, material at the retreating side moves slightly in backward direction. The material deformation and the peak temperature influence on the microstructural characters and can determine the width of SZ. Based on the simulation, effective strain and temperature histories of material around the tool pin were also calculated. The amount of effective strain and peak temperature required for recrystallization at the advancing and retreating sides as well as at the bottom of SZ was determined. Therefore, the width of SZ can be predicted by the simulation.     

AZ91D镁合金超疏水膜层的制备及其表征

采用简单易行的化学刻蚀方法,通过硝酸刻蚀、化学镀银和硬脂酸自组装改性处理,在AZ91D镁合金表面上成功制备出了超疏水膜层,进一步解释了该制备工艺的化学反应机理。利用扫描电子显微镜和视频光学接触角测量仪对AZ91D镁合金表面超疏水膜层的微观形貌和润湿性能进行了表征,利用能谱仪和光谱仪测定了膜层的表面化学组成。结果显示,釆用上述方法处理后的AZ91D镁合金表面呈现出良好的疏水性,水滴在试样表面的表观接触角为153°,滚动角为4°。     

Finite element analysis of rotary-die equal channel angular pressing

In this paper, the finite element method (FEM) was applied to analyze the plastic flow and strain hardening behavior of pure copper, subjected to rotary-die equal channel angular pressing (RD-ECAP) up to four passes. The die was rotated 90° counter clockwise between the passes in the simulation. The effective strain distribution and load–stroke curves were investigated. The load was increased with the number of rotary-die equal channel angular pressing passes. The results show that, plastic deformation becomes inhomogeneous with the number of passes due to an end effect, which was not found seriously in conventional equal channel angular pressing (ECAP). Especially, decreasing corner gap with increasing the number of passes was observed and explained by the strain hardening effect.     

Plastic deformation characteristics of cross-equal channel angular pressing

For the first time, the plastic deformation characteristics of cross-equal channel pressing (cross-ECAP), a modified equal channel angular pressing, using a cross-shaped channel instead of a conventional l-shaped channel, was analyzed by using finite element analysis. The deformation in the cross-ECAP is more complicated and the strain induced is much more severe than that in the conventional ECAP. However, the plastic strain is localized in the central linear region of the workpiece and very small strain is developed in the edge regions, which is in good agreement with experimental results in the literature showing nonuniformity in microstructure and hardness distribution. The load requirements of cross-ECAP are much higher in comparison to conventional ECAP and T-ECAP processes.     

AZ91及AZ91-Y合金复合干摩擦性能的对比

为了探究AZ91镁合金的复合干摩擦行为,以未淬火45钢为摩擦副,在不同载荷下(100,200,300 N),开展AZ91及Y含量为1.0%(质量分数)合金的复合干摩擦实验。采用OM,XRD,SEM等观察合金的磨损形貌并分析磨损机理。结果表明:增加法向载荷,两试样复合磨损率线性增加但摩擦因数却逐渐减小;Al 2Y硬质颗粒可细化晶粒、弱化相界面开裂倾向以提高AZ91-Y合金耐磨性。100,300 N法向载荷下,AZ91-Y合金主要磨损机制分别为磨粒磨损和剥离磨损,与基体(AZ91)一致,其磨损率分别降低了21.7%和5.9%。     

Interfacial reactions between AZ91D magnesium alloy and plaster mould material during investment casting

Abstract

Reactions at the mould/metal interface play an important role in determining the quality of investment castings. They are particularly critical in the case of magnesium alloys cast in industrial plaster moulds. In this work, reactions of molten magnesium alloy with plaster mould were studied. First the potential interactions with mould materials (including gases) were examined using thermodynamic considerations. Then thin sheets of AZ91D magnesium alloy were cast in industrial plaster moulds using vacuum assistance: the surface of sheets and plaster mould were characterised. The analysis of reaction products indicates that magnesium vapours diffuse through the plaster and reduce the silica present in the investment material according to the following reaction: 4Mg + SiO₂=2MgO + Mg₂Si. The extent of reactions is controlled by mould temperature and thickness of castings.     

Effects of extrusion and equal channel angular pressing on the microstructure,tensile and fatigue behaviour of the wrought magnesium alloy AZ80

The microstructure, mechanical properties, fatigue life and fatigue crack propagation rate of Mg‐8Al‐0.5Zn‐0.3Mn (AZ80) magnesium alloy were investigated after extrusion and equal channel angular pressing (ECAP). The highest ultimate and yield strengths and a large enhancement in the fatigue lifetime were obtained after two passes of ECAP. These were decreased with further pressing, although the grain size became finer. There was a correlation between the fatigue and ultimate strengths of AZ80 alloy. The transition from twinning to dislocation slip has also occurred at an average grain size of 7.9 μm. Simultaneous influences of the grain size and the yield strength caused an almost the same threshold of the stress intensity ratio for different process conditions. Moreover, the enhanced ductility of the ECAPed alloy resulted in an increase in the crack growth resistance because of its better ability to accommodate plastic strains during cycling.