关键词： 镁合金   汽车车架   Ti   微合金化   显微组织   力学性能  

摘要： 研究了不同钛含量的汽车车架用含钛镁合金Mg-8Al-1Zn-x Ti(x=0.05, 0.15, 0.3)的显微组织和力学性能,并对比了不含钛Mg-8Al-1Zn合金的显微组织和力学性能。结果表明:钛的添加,细化了合金晶粒,改善了合金力学性能。随钛含量增加,合金平均晶粒尺寸先减小后增大、力学性能先提高后下降。与不含钛Mg-8Al-1Zn合金相比,含钛Mg-8Al-1Zn-0.15Ti合金的平均晶粒尺寸减小7.2μm、抗拉强度增大32 MPa、屈服强度增大33 MPa、断后伸长率增大3.8%,拉伸断裂方式从混合断裂变为塑性断裂。

关键词： friction stir welding   flexural strength   grain size   magnesium alloys   surface roughness   tensile strength  

摘要： Magnesium alloys are lightweight structural material with attractive specific strength and require joining of different pieces in many industrial applications. Due to their low melting temperature, chemically active elements and high thermal expansion these alloys are difficult-to-weld by conventional welding techniques. Friction Stir Welding has favorable characteristics to weld these alloys but dissimilarity in workpieces pose problem to achieve required weld characteristics. The present research experimentally investigates the weld characteristics in Friction Stir Welding of dissimilar AZ31 and AZ91 Mg alloys under varying processing parameters. The research outcomes show that shoulder diameter and rotational speed of tool were the most influencing parameters followed by welding speed in most of the cases. Grain size increases with increase in rotational speed and shoulder diameter. There was no presence of intermetallic compound in stir zone but some cracks were observed. Maximum tensile strength in weld zone was 89.71% and all the tensile samples break from 1 to 3 mm away from weld center line. Maximum average microhardness and flexural strength were 72.51 +/- 6.82 HV and 380.06 +/- 13.43 MPa, respectively, while flexural load vs elongation curve was almost similar to base material.

关键词： corrosion   magnesium alloys   Mg17Al12   roughness  

摘要： In this work, the effect of surface roughness, induced by milling operation, on the corrosion properties of the as-cast AZ31 and the as-cast AZ80 magnesium alloys has been studied. The surface roughness was measured with varying feed rate (21, 200 and 320 mm/min) and cutting speed (100, 640 and 1330 rpm) at a constant depth of cut for both the alloys. The variation in the surface roughness has been correlated with the hardness, ductility and volume fraction of the Mg17Al12 precipitates in both the alloys. The corrosion behavior has been evaluated by conducting immersion test in a freely aerated 3.5 wt.% NaCl solution. The corrosion rates have been observed to be directly related to the surface roughness. The higher corrosion resistance of the machined AZ80 alloy as compared to the AZ31 alloy has been ascribed to the combined effect of the lower surface roughness and the partial dissolution of Mg17Al12 eutectic precipitates in the AZ80 alloy due to the increase in the temperature during milling, which was calculated analytically.

关键词： Swing friction stir spot welding   Bonding mechanism   Microstructure   Fracture morphology  

摘要： Swing friction stir spot welding (SFSSW) technology which is mainly consisted of two steps is applied to join AA5083 Al alloy to AZ31B Mg alloy in the present investigation. In addition, AA5083/AZ31B joints produced by conventional FSSW were obtained. Optical microscope, scanning electron microscope equipped with energy-dispersive X-ray spectroscope, and X-ray diffraction pattern were used to analyze the morphology and microstructure of different joints. Lap-shear tensile testing and microhardness measurements were conducted to evaluate the joint performance. Results show that the bonding area and the material mixing of the spot welds fabricated by SFSSW technology were both promoted in comparison with that made by conventional FSSW. The thickness of intermetallic compounds (IMCs) at the interface around the filled original keyhole was larger owing to more heat input. The bonding interface of SFSSWed joints was irregular, and the IMCs along the annular interface were thinner than that produced by conventional FSSW. The IMC structure in the interface layer of SFSSWed joints is spherical, which is different from the dendritic structure by conventional FSSW. Finally, IMCs were found in the weld zone through phase analysis by XRD and microhardness measurements of SFSSWed joints. The fracture modes and morphologies were different to two joints, and the lap-shear tensile load of SFSSWed joint was 72.95% larger than the conventional FSSWed joint.

关键词： Magnesium alloy   Cylindrical parts with longitudinal inner ribs   Hot backward flow forming   Deformation mechanism  

摘要： Thin-walled cylindrical parts with longitudinal inner ribs (CPLIRs) made of magnesium alloys are one of the most promising lightweight components. Flow forming is an effective technology to realize the integrated manufacturing of thin-walled CPLIRs. However, due to the complicated material flow and narrow temperature window, defects like insufficient filling at the rib groove and concavity of the back of rib occur easily during hot backward flow forming (HBFF) of ZK61 alloy thin-walled CPLIRs. The isothermal uniaxial compression test was proposed as the physical simulation test of the HBFF of thin-walled CPLIRs, and a novel method for analyzing the formability of hot spin-forming was proposed on the basis of the combination of 3D hot processing maps (HPMs) and finite element (FE) simulation. The process experiment and FE simulation integrated with 3D HPMs were conducted to investigate the deformation characteristic and material flow, and formation mechanism of defects was revealed. Further, the influence of process parameters on the power dissipation efficiency of spun workpiece was discussed. The results show that safe deformation of the alloy is concentrated at a narrow region with high temperature and low strain rate;the large tangential flow at the cylindrical wall and radial flow at the inner rib contributed to the filling of rib groove;unsaturated inner rib and concavity of the outer wall at the back of rib are typical defects;the ZK61 alloy CPLIRs exhibits good formability under reasonable process parameters, which is beneficial for obtaining qualified forming quality and uniform recrystallized microstructure.

关键词： Al-AlN master alloy   AlN   AZ91 composites   mechanical properties   microstructures  

摘要： AlN particle-reinforced Mg-Al matrix composites are fabricated by introducing an Al-AlN master alloy in Mg melt during casting. The microstructure, tensile strength, and fracture behavior of the AlN/AZ91 composites are investigated. The introduction of AlN results in a modified dendrite morphology of the beta-Mg17Al12 phase and, thus, improves the mechanical properties of the AZ91 alloy. The results show that 2% (by weight) AlN reinforcement has the highest tensile strength and elongation, mainly due to the reduction of the size of the second phase and the uniform distribution. Consequently, compared to as-cast AZ91 alloys, the strength and elongation of the AlN/AZ91 composites increase by 34% and 171%, respectively. For second-phase beta-Mg17Al12, the enhancement mechanism and size model are constructed, and the model trends are analyzed, predicted, and verified experimentally.

关键词： axon outgrowth   CNTs-CaP   CS-AZ91D   dorsal root ganglia   ERK signalling pathway   neurotrophic factor  

摘要： Increasing attention has been paid on the application of biodegradable materials such as magnesium and its alloys in neuron repair. AZ91D magnesium alloy coated with carbon nanotubes (CNTs) and/or calcium phosphate (CaP)/chitosan (CS) was fabricated in this study. To evaluate the bioactivity of these AZ91D-based composites, the extracts were prepared by immersing samples in modified simulated body fluid (m-SBF) for 0, 2, 8, 16, 24, 34, 44, 60, or 90 days. Immunofluorescence staining for neuronal class III beta-tubulin (TUJ1) revealed that both CNTs-CaP/CS-AZ91D and CaP/CS-AZ91D extracts promoted axon outgrowth of dorsal root ganglia (DRG) neurons, accompanied with increased expression of phosphorylated focal adhesion kinase (p-FAK) and growth associated protein-43 (GAP-43). Besides, the extracts increased the expression and the release of neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). ERK signalling was activated in DRG neurons after treating with either CNTs-CaP/CS-AZ91D or CaP/CS-AZ91D extracts, and its inhibition with U0126 counteracted the beneficial effects of these extracts on DRG neuron. Overall, the extracts from these AZ91D-based composites might promote DRG neuron growth via activating ERK signalling pathway. Notably, CNTs-CaP/CS-AZ91D extracts showed a better promoting effect on neuron growth than CaP/CS-AZ91D. Assessment of ion elements showed that the addition of CNTs coating enhanced magnesium corrosion resistance and reduced the deposition of calcium and phosphorus on the surface of CaP/CS-AZ91D alloy. These findings demonstrate that CNTs-CaP/CS-AZ91D likely provide a more suitable environment for neuron growth, which suggests a potential implantable biomaterial for the treatment of nerve injury. Significance AZ91D magnesium alloy coated with carbon nanotubes (CNTs) and/or calcium phosphate (CaP)/chitosan (CS) was fabricated and their immersion extracts were prepared using modified simulated body

关键词： Magnesium alloys   Corrosion resistance   Conversion coatings   Pretreatment  

摘要： Alx(Mn,Fe)y phase, as a common derivative of Fe-containing impurities, significantly deteriorates the protectiveness of phosphate conversion coatings (PCC) on magnesium alloys due to the micro-galvanic effect. This work presents a novel pretreatment method, aiming at chemically depleting the noble Alx(Mn,Fe)y phase from Mg alloy surface before PCC treatment. The pretreatment bath contains both oxidant and complexing agent, with the pH value and concentration of different constituents being determined by thermodynamic calculation. The corrosion resistance of PCC being preceded by exploiting the novel pretreatment method was improved, which was attributed to the mitigation of micro-galvanic corrosion.

关键词： AZ91 magnesium alloy   Nanocomposite   Squeeze-casting   Tensile properties   Strain hardening   Strengthening mechanism  

摘要： The present work investigates the effect of SiC nanoparticles (SiCnp) additions on the tensile properties of the squeeze-cast AZ91 + 2.0Ca + 0.3Sb (wt%) alloy at ambient, 423 K and 473 K temperatures. All the AZ91 + 2.0Ca + 0.3Sb + xSiC(np) [x = 0.5 wt% (0.29 vol%), 1.0 wt% (0.58 vol%), and 2.0 wt% (1.16 vol%)] nanocomposites illustrate greater yield strength and ultimate tensile strength in contrast to the AZ91 + 2.0Ca + 0.3Sb alloy at all the temperatures employed. The yield strength, ultimate tensile strength and elastic modulus of both the alloy and the nanocomposites decline as the temperature increases, whereas the work to fracture increases with a rise in temperature. Among the nanocomposites, the one comprising of 2.0SiC(np) demonstrates the best tensile properties. All the nanocomposites display superior strain hardening response than the alloy, and the maximum strain hardening is perceived in the AZ91 + 2.0Ca + 0.3Sb + 2.0SiC(np) nanocomposite. The improved tensile properties of the nanocomposites are ascribed to the reduced grain size, the increase in dislocation density owing to Coefficient of Thermal Expansion (CTE) mismatch between the alloy and the SiC nanoparticles, the Orowan strengthening as well as the presence of a relatively higher amount of Al2Ca phase in the nanocomposites. The contribution to the improvement of strength of the nanocomposites in decreasing order of their influence are the strengthening due to CTE mismatch, the Hall-Petch strengthening, and Orowan strengthening. The fracture surfaces of the tensile specimens tested at 298 K confirmed the presence of transgranular cleavage fracture which remained unchanged at 473 K as well.

关键词： Micro-arc oxidation   Magnesium alloy   Preparation   Molybdate coating   Conversion  

摘要： In order to enhance the corrosion resistance of molybdate conversion coating, the molybdate coating is subjected to micro-arc oxidation treatment in electrolyte with Na2SiO3 as a main salt. The electrochemical behavior and corrosion weight loss of different coating were studied. The surface morphology, element composition, roughness and phase composition of different coatings were analyzed by SEM, EDS, laser confocal microscopy and XRD, the growth process of different micro-arc oxidation coatings was explored. The results shows that the arcing voltage of the molybdate coating enhanced by micro-arc oxidation is significantly reduced, the corrosion potential is shifted to the right, and the corrosion weightlessloss of the coating is the lowest, compared with the molybdate coating and the micro-arc oxidation coating. Micro-arc oxidation on the surface of the molybdate coating is beneficial to the formation of MgAl2O4 and the production of new phase is MoSi2, which can better improve the corrosion resistance of the molybdate coating. The micro-arc oxide coating does not form a ceramic film with a pore structure at the moment of arcing. As the micro-arc oxidation time prolongs, the ceramic film is gradually formed. When the time reaches 60 s, the ceramic film is completely formed. Graphic In this paper, micro-arc oxidation treatment is performed on the basis of molybdate conversion coating to obtain micro-arc oxidation enhanced molybdate coating. The experiment is mainly divided into three parts: the first part, molybdate conversion treatment of the magnesium alloy substrate to obtain a molybdate conversion coating. The second part, the micro-arc oxidation treatment is performed on the surface of the molybdate coating, and discharge channels appear on the surface. The third part, micro-arc oxidation enhanced molybdate coating is obtained.