β锻造Ti-6Al-4V合金力学性能各向异性

研究β锻造Ti-6Al-4V(Ti64)合金拉伸性能和断裂韧性的各向异性。对饼材不同取向的显微组织和晶体学织构进行分析,同时研究取样方向对拉伸性能、断裂韧性的影响。结果表明,Ti64饼材原始β晶粒呈扁平状。室温下合金主要由α相构成,β锻造后β→α相变产生的多个α相变体导致α相织构强度较低。力学性能各向异性的主要影响因素为原始β晶粒形貌以及与α织构相关的滑移。采用J积分阻力曲线法测定合金的起裂韧性,并将起裂韧性KJIC分为内在韧性和外在韧性。内在断裂韧性各向异性主要与原始β晶粒对裂纹尖端塑性区范围的影响相关;外在断裂韧性主要与α片层与集束对裂纹曲折程度的影响相关。

Effect of phosphate conversion film on fatigue and corrosion fatigue behavior of an as-rolled Mg–3.08Zn–0.83Al(in wt.%)alloy

Through investigating and comparing the fatigue behavior of an as-rolled Mg–3.08Zn–0.83Al(in wt.%)alloy performing surface phosphate conversion film treatment,it revealed that the determined fatigue strength of surface treated samples at 106 cycles in air was 65 MPa,whereas the fatigue strength was only 35 MPa when tested in 3.5 wt.%NaCl solution.Failure analysis demonstrated that in air,the fatigue crack initiation was mainly dominated by the interaction between the retarding effect of phosphate conversion film on cyclic slips occurring in the underneath substrate.When the matrix cannot endure the accumulated stress concentration due to the irreversibility of cyclic slips,the fatigue crack will preferentially initiate at sample subsurface.Since the phosphate conversion film cracked easily under the cyclic loading and lost its protectiveness on the substrate in 3.5 wt.%NaCl solution,fatigue cracks were preferentially nucleated at the localized corrosion pits.

Research Progress on the Corrosion Behavior of Magnesium-Lithium-Based Alloys: A Review

In this review paper, the research progress on corrosion behavior of hexagonal close-packed(HCP) singular phase, body cubic-centered(BCC) singular phase and(HCP + BCC) duplex-structured Mg–Li alloys has been summarized and reviewed, and the future trend about the studies on corrosion behavior of Mg–Li-based alloys and possible solving methods for the improvement in corrosion resistance are discussed also.

In vitro corrosion resistance and antibacterial performance of noveltin dioxide-doped calcium phosphate coating on degradable Mg-1Li-1Ca alloy

A SnO_2-doped calcium phosphate(Ca-P-Sn) coating was constructed on Mg-1 Li-1 Ca alloy by a hydrothermal process. The fabricated functional coatings were investigated using scanning electron microscopy(SEM), X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FT-IR). A triple-layered structure, which is composed of Ca_3(PO_4)_2,(Ca, Mg)_3(PO_4)_2, SnO_2, and MgHPO_4·3 H_2O, is evident and leads to the formation of Ca_(10)(PO_4)_6(OH)_2 in Hank's solution. Electrochemical measurements, hydrogen evolution tests and plating counts reveal that the corrosion resistance and antibacterial activity were improved through the coating treatment. The embedded SnO_2 nanoparticles enhanced crystallisation of the coating.The formation and degradation mechanisms of the coating were discussed.

Exfoliation corrosion of extruded Mg-Li-Ca alloy

Exfoliation on as-extruded Mg-1 Li-1 Ca magnesium alloy was investigated after an immersion in 3.5 wt%NaCl aqueous solution for 90, 120 and 150 days through optical microscope, digital camera, scanning electron microscope, electrochemical workstation, scanning Kalvin probe, X-ray diffraction and Fourier transform infrared spectroscope. The results demonstrated that exfoliation corrosion occurred on extruded Mg-1 Li-1 Ca alloy due to elongated microstructure parallel to surface, and delamination of lamellar structure resulted from galvanic effect and wedge effect. Skin layer with fine grains exhibited better corrosion resistance, whereas the interior with coarse grains and the intermetallic compound,Mg2 Ca particles existing in a fibrous structure, dispersed along grain boundaries and extrusion direction in a line. Furthermore, galvanic effect between Mg2 Ca particles and their neighboring a-Mg matrix facilitated dissolution of Mg2 Ca particles and a-Mg matrix; wedge effect was caused by formation of corrosion products. Exfoliation corrosion of extruded Mg-Li-Ca alloys might be a synergic effect of pitting corrosion,filiform corrosion, intergranular corrosion and stress corrosion. Finally, exfoliation corrosion mechanism was proposed.

Dealloying corrosion of anodic and nanometric Mg41Nd5 in solid solution-treated Mg-3Nd-1Li-0.2Zn alloy

The microstructure and chemical compositions of the solid solution-treated Mg-3 Nd-1 Li-0.2 Zn alloy were characterized using optical microscope,scanning electron microscope(SEM),transmission electron microscope(TEM),electron probe micro-analyzer(EPMA)and X-ray photoelectron spectroscopy(XPS).The corrosion behaviour of the alloy was investigated via electrochemical polarization,electrochemical impedance spectroscopy(EIS),hydrogen evolution test and scanning Kelvin probe(SKP).The results showed that the microstructure of the as-extruded Mg-3 Nd-1 Li-0.2 Zn alloy containedα-Mg matrix and nanometric second phase Mg_(41)Nd_(5).The grain size of the alloy increased significantly with the increase in the heat-treatment duration,whereas the volume fraction of the second phase decreased after the solid solution treatment.The surface film was composed of oxides(Nd_(2)O_(3),Mg O,Li_(2)O and Zn O)and carbonates(Mg CO3 and Li_(2)CO3),in addition to Nd.The as-extruded alloy exhibited the best corrosion resistance after an initial soaking of 10 min,whereas the alloy with 4 h-solution-treatment possessed the lowest corrosion rate after a longer immersion(1 h).This can be attributed to the formation of Nd-containing oxide film on the alloys and a dense corrosion product layer.The dealloying corrosion of the second phase was related to the anodic Mg_(41)Nd_(5)with a more negative Volta potential relative toα-Mg phase.The preferential corrosion of Mg_(41)Nd_(5)is proven by in-situ observation and SEM.The solid solution treatment of Mg-3 Nd-1 Li-0.2 Zn alloy led to a shift in corrosion type from pitting corrosion to uniform corrosion under long-term exposure.

Influence of Zn Content on Microstructure and Tensile Properties of Mg–Zn–Y–Nd Alloy

In the present study,the effect of Zn content on the microstructure and deformation behavior of the as-cast Mg-Zn-Y-Nd alloy has been investigated.The results showed that as Zn content increased,the volume fraction of secondary phases increased.Moreover,the phase transformation from W-phase to W-phase and I-phase occurred.In the as-cast state,W-phase exists as eutectic and large block form.When Zn content increases to 6 and 8%（wt%）,small I-phase could precipitate around W-phase particles.Additionally,the effect of Zn content on the tensile properties and deformation behavior varies with the testing temperature.At room temperature,the tensile strength increases with Zn content,whereas the elongation increases initially and then decreases.At 250℃,as Zn content increases,the tensile strength decreases initially and then increases slightly,whereas the elongation decreases.At 350℃,the elongation increases with Zn content,whereas the tensile strength decreases initially and then increases slightly.

Analysis and Modeling of Friction Stir Processing-Based Crack Repairing in 2024 Aluminum Alloy

Abstract A friction stir processing-based method was used to repair cracks in the 2024 aluminum alloy plates. The temperature field and plastic material flow pattern were analyzed on the basis of experimental and finite element simulation results. Microstructure and tensile properties of the repaired specimens were studied. The results showed that the entire crack repairing was a solid-phase process and plastic materials tended to flow toward the shoulder center and then resulted in the repairing of cracks. Meanwhile, the coarse grain structures were refined in repaired zone （RZ）, while the grains in thermal-mechanically affected zone and heat-affected zone were elongated and driven to grow up. Meanwhile, large phases are crushed into small particles and dispersed inside the RZ. Finally, the strength of the repaired specimens can be restored dramatically and their ductility can be partially restored. After heat treatment, the tensile properties of the repaired specimens can be further enhanced.