Damping performance of SiC nanoparticles reinforced magnesium matrix composites processed by cyclic extrusion and compression

This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite(SiC_(np)/AZ91D)processed by cyclic extrusion and compression(CEC).It was found that the CEC process significantly affects the damping performance of the composite due to alterations in the density of dislocations and grain boundaries in the matrix alloy.Although there would be dynamic precipitation of the Mg17Al12 phase during processing which increases the phase interface and limits the mobility of dislocations and grain boundaries.The results also showed that the damping capacity of 1%SiC_(np)/AZ91D composite continuously decreases with adding CEC pass number and it consistently increases with rising the applied temperature.Considering the first derivative of the tanδ-T curve,the dominant damping mechanism based on test temperature can be divided into three regions.These three regions are as follows(i)dislocation vibration of the weak pinning points(≤T_(cr)),(ii)dislocation vibration of the strong pinning points(T_(cr)∼T_(V)),and(iii)grain boundary/interface sliding(≥T_(V))

High temperature mechanical behavior of low-pressure sand-cast Mg-Gd-Y-Zr magnesium alloy

The aim of this work is firstly to optimize T6 heat-treatment of low-pressure sand-cast Mg-10Gd-3Y-0.5Zr alloy,and then systematically investigate the mechanical behavior of the T6-treated alloy from room temperature to 300℃.It turned out that the optimum T6 heat-treatments for the tested alloy are 525℃×12 h+225℃×14 h and 525℃×12 h+250℃×12 h which integrated age-hardening and tensile properties into account,respectively.The strength of the T6-treated alloy indicates obvious anomalous temperature dependence from room temperature to 300℃,namely both ultimate tensile strength and yield strength of the tested alloy firstly increase with tensile temperature,and then decrease as temperature increases further.Elongation increased with temperature monotonously.The tensile fracture mode of the tested alloy changes from transgranular fracture to intergranular fracture with the increasing of test temperature.

In vitro and in vivo evaluations of Mg-Zn-Gd alloy membrane on guided bone regeneration for rabbit calvarial defect

To develop a biodegradable membrane with guided bone regeneration(GBR),a Mg-2.0Zn-1.0Gd alloy(wt.%,MZG)membrane with Ca-P coating was designed and fabricated in this study.The microstructure,hydrophilicity,in vitro degradation,cytotoxicity,antibacterial effect and in vivo regenerative performance for the membrane with and without Ca-P coating were evaluated.After coating,the membrane exhibited an enhance hydrophilicity and corrosion resistance,showed good in vitro cytocompatibility upon MC3T3E-1 cells,and exhibited excellent antibacterial effect against E.coli,Staphylococcus epidermis and Staphylococcus aureus,simultaneously.In vivo experiment using the rabbit calvarial defect model confirmed that Ca-P coated MZG membrane underwent progressive degradation without inflammatory reaction and significantly improved the new bone formation at both 1.5 and 3 months after the surgery.All the results strongly indicate that MZG with Ca-P coating have great potential for clinical application as GBR membranes.

Effects of Cu content on microstructure and mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys

A systematic study on how Cu content affects the microstructure and mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys during solution treatment and ageing heat treatment was conducted.The swirled enthalpy equilibrium device(SEED)was adopted to prepare the semi-solid slurry of Al-6Zn-2Mg-xCu alloys.The microstructure development and mechanical properties were studied using optical microscopy(OM),scanning electron microscopy(SEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),as well as hardness and tensile testing.The grain boundary and shape factor were calculated using image processing software(Image-Pro Plus 6.0).Results show that the alloys are composed of typical globular primaryα-Al grains,eutectic phases,and smaller secondaryα-Al grains.After solution and ageing heat treatment,the eutectic phases are dissolved into Al matrix when the Cu content is lower than 1.5wt.%,while some eutectic phases transform into Al_(2)CuMg(S)phases and remain at grain boundaries when Cu content reaches 2wt.%.T6 heat treatment significantly enhances the mechanical properties of rheo-diecasting Al-6Zn-2Mg-xCu alloys.When Cu concentration is 0.5wt.%-1.5wt.%,the ultimate tensile strength,yield strength and elongation of T6 treated alloys rise to around 500 MPa,420 MPa,and 18%,respectively.

Achieving grain refinement ofα-Al and Si modification simultaneously by La-B-Sr addition in Al-10Si alloys

As-cast Al-Si alloys always face low ductility because of coarseα-Al grains and large lamellar eutectic Si.Although B-containing refiners and Sr modifiers could refine theα-Al grains and eutectic Si respec-tively,simultaneous addition leads to an invalid effect of Sr because B-containing refiner has a poison-ing effect(PE)on Sr modifier in the Al-10Si-B-Sr alloys.The present work achieves both refinement ofα-Al grains and modification of Si merely by the addition of 500 ppm La in Al-10Si-0.02B-0.015Sr alloy,which greatly enhances the ductility and tensile strength.Sr-B interaction in the Al-10Si-0.02B-0.015Sr melt results in a consumption of Sr by forming Sr-B intermetallic compound.CALPHAD-type calculations reveal that Sr concentration in liquid before eutectic reaction becomes a key parameter to estimate the alloying modification effect.The addition of La forms LaB 6 and thereby releases Sr to protect the Sr modification effect.First-principles calculations illustrate that both Sr and La are benefi-cial to the formation of twin boundaries in Si particles due to their negative formation energy of twin boundaries.The formed LaB 6 has a semicoherent interface withα-Al with the orientation relationship of[110]_(LaB6)//[110]_(Al) and(111)_(LaB6)//(111)_(Al),demonstrating that LaB 6 is an efficient nucleation site forα-Al,which contributes to the refinement ofα-Al in the Al-10Si-0.05La-0.02B-0.015Sr alloy.Our findings re-veal the micro-mechanism of refinement during the solidification process and develop an effective and simple way to obtain high-performance Al alloys.

Effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy

This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5 Y（wt%） alloy, which was prepared by casting, and then homogenized and rolled at 200℃. The rolling process was conducted with 10% reduction per pass and five different accumulated strains, varying from 10% to 70%. The results indicate that the as-cast and as-rolled Mg-8Li-3Al-2Zn-0.5Y alloys are composed of α-Mg, β-Li, AlLi and Al;Y phases. After rolling process,anisotropic microstructure was observed. a-Mg phase got elongated in both rolling direction and transverse direction with the addition of rolling strain. Consequently, the strength of the alloy in both directions was notably improved whereas the elongation declined, mainly caused by strain hardening and dispersion strengthening. The tensile properties of the as-rolled alloys in the RD, no matter the YS, UTS or the elongation, are higher than those of the TD due to their larger deformation strain and significant anisotropy in the hcp α-Mg phase. In addition, the fracture and strengthening mechanism of the tested alloys were also investigated systematically.

Effect of Cu addition on microstructures and tensile properties of high-pressure die-casting Al-5.5Mg-0.7Mn alloy

In this study, Cu was added into the high-pressure die-casting Al-5.5 Mg-0.7 Mn(wt%) alloy to improve the tensile properties. The effects of Cu addition on the microstructures, mechanical properties of the Al-5.5 Mg-0.7 Mn alloys under both as-cast and T5 treatment conditions have been investigated. Additions of 0.5 wt%, 0.8 wt% and 1.5 wt% Cu can lead to the formation of irregular-shaped Al2 CuMg particles distributed along the grain boundaries in the as-cast alloys. Furthermore, the rest of Cu can dissolve into the matrixes. The lath-shaped Al2 CuMg precipitates with a size of 15–20 nm × 2–4 nm were generated in the T5-treated Al-5.5 Mg-0.7 Mn-x Cu(x = 0.5, 0.8, 1.5 wt%) alloys. The room temperature tensile and yield strengths of alloys increase with increasing the content of Cu. Increasing Cu content results in more Al2 CuMg phase formation along the grain boundaries, which causes more cracks during tensile deformation and lower ductility. Al-5.5 Mg-0.7 Mn-0.8 Cu alloy exhibits excellent comprehensive tensile properties under both as-cast and T5-treated conditions. The yield strength of 179 MPa, the ultimate tensile strength of 303 MPa and the elongation of 8.7% were achieved in the as-cast Al-5.5 Mg-0.7 Mn-0.8 Cu alloy, while the yield strength significantly was improved to 198 MPa after T5 treatment.

Microstructure and mechanical properties of sand-cast Mg-6Gd-3Y-0.5Zr alloy subject to thermal cycling treatment

This work was undertaken to investigate the microstructural evolution, mechanical properties and fracture behavior of sand-cast Mg-6 Gd-3 Y-0.5 Zr(GW63) alloy subject to thermal cycling treatment. In order to simulate the thermal cycling under extreme service conditions(space or moon environments), the sand-cast and T6 treated GW63 alloys were subjected to thermal cycling treatment which consists of deep cryogenic-elevated temperature cycling treatment(DCET) and deep cryogenic cycling treatment(DCT). Results indicate that there are significant gains in yield strength(YS) and ultimate tensile strength(UTS) of the sand-cast GW63 alloy after DCET, whereas the T6 state alloy undergoes a different variation in mechanical properties. However, no appreciable influence is revealed on the mechanical properties of the tested GW63 alloys after DCT. Meanwhile, the DCT and DCET have no obvious effects on the fracture morphology. The DCT enhances the precipitation kinetics via providing favorable nucleation sites for the precipitation of second phases. The elevated temperature process of DCET plays a crucial role in improving the aging-hardening responses and releasing the stress concentration brought by DCT to a great extent, leading to overcome the obstacle of essential phase transformation. The changes in mechanical properties are primarily attributed to the phase transformation of the studied alloys during DCET.

Effects of Gd Addition on the Microstructure and Tensile Properties of Mg–4Al–5RE Alloy Produced by Three Different Casting Methods

This work deals with the effect of 0.67 wt%Gd addition on the microstructure and tensile properties of Mg–4 Al–5 RE(where RE represents La–Ce mischmetal)alloy produced by sand casting(SC),permanent mold casting(PMC),and high-pressure die casting(HPDC).The results show that Gd addition could refine the grains,but its efficiency decreases by increasing the cooling rate due to the shifting from SC to PMC and finally to the HPDC method.Meanwhile,the acicular Al11 RE3 phase is modified into the short-rod or granular-like shape under the three casting conditions.Such refined and modified microstructures are due to the Al2(Gd,RE)phases,which act as the nucleation sites in both theα-Mg matrix and Al11 RE3 phase.Also,the weakening grain refinement effect in the increased cooling rates can be attributed to the narrow constitutional undercooling zone.After Gd addition,the 0.2%proof strength of the SC and PMC alloys increases by about 16.9%and 12.7%,respectively,while in the HPDC alloy,it decreases by about 5.9%.The main factor in the strength increment of the SC and PMC alloys is the grain boundary strengthening due to grain refinement which is proved by modeling the related mechanisms,whereas weak secondary phases and grain boundary strengthening mechanisms in the HPDC alloy lead to strength reduction.After Gd addition,the elongation to failure of the SC,PMC,and HPDC alloys is significantly enhanced by about 34.8%,20.2%,and 12.3%,respectively,due to the crack resistance nature of the modified short-rod/granular Al11(RE,Gd)3 phase compared to the acicular one.

Effect of Zn Addition on the Microstructure and Mechanical Properties of Cast Mg-10Gd-3.5Er-xZn-0.5Zr Alloys

In this work,the effects of Zn content(0-2 wt%)on microstructural evolution and mechanical properties of cast Mg-10Gd-3.5Er-0.5Zr alloys are studied.The results show that the as-cast Mg-10Gd-3.5Er-xZn-0.5Zr alloys are mainly composed of Mg matrix and secondary(Mg,Zn)3(Gd,Er)phases distributed along grain boundaries.With the increase in Zn content,the volume fraction of secondary(Mg,Zn)3(Gd,Er)phases increases and the grains get refined.In the process of solid solution treatment,Zn addition can lead to the formation of long-period stacking ordered(LPSO)structures and the volume fraction of LPSO structures increases with Zn content.In addition,the Zn addition can reduce the vacancy formation energy and accelerate the diffusion rate of RE elements in Mg matrix.Because of the comprehensive effect of secondary phases and the accelerated diffusion rate,the base alloy and 2Zn alloy have less grain growth after solid solution treatment than that of the 0.5Zn alloy and 1 Zn alloy.The precipitation process is also accelerated by enhanced diffusion rate.At room temperature(RT),the strengthening effect of β’+β1 precipitates is more effective than that of LPSO structures,so the peak-aged 0.5Zn alloy exhibits the most excellent mechanical performance at RT,with yield strength of 219 MPa,ultimate tensile strength 296 MPa and elongation of 6.4%.While LPSO structures have stronger strengthening effect at elevated temperature than that of β’+β1 precipitates,so the 1Zn alloy and 2Zn alloy have more stable mechanical performance than that of the base alloy and 0.5Zn alloy with the increase in tensile temperature.

Development of High Strength and Toughness Non-Heated Al–Mg–Si Alloys for High-Pressure Die-Casting

Based on the 3 factors and 3 levels orthogonal experiment method,compositional effects of Mg,Si,and Ti addition on the microstructures,tensile properties,and fracture behaviors of the high-pressure die-casting Al-x Mg-y Si-z Ti alloys have been investigated.The analysis of variance shows that both Mg and Si apparently infl uence the tensile properties of the alloys,while Ti does not.The tensile mechanical properties are comprehensively infl uenced by the amount of eutectic phase(α-Al+Mg2Si),the average grain size,and the content of Mg dissolved intoα-Al matrix.The optimized alloy is Al-7.49 Mg-3.08 Si-0.01 Ti(wt%),which exhibits tensile yield strength of 219 MPa,ultimate tensile strength of 401 MPa,and elongation of 10.5%.Furthermore,contour maps,showing the relationship among compositions,microstructure characteristics,and the tensile properties are constructed,which provide guidelines for developing high strength and toughness Al–Mg–Si–Ti alloys for high-pressure die-casting.

Research and development strategy for biodegradable magnesium-based vascular stents:a review

Magnesium alloys are an ideal material for biodegradable vascular stents,which can be completely absorbed in the human body,and have good biosafety and mechanical properties.However,the rapid corrosion rate and excessive localized corrosion,as well as challenges in the preparation and processing of microtubes for stents,are restricting the clinical application of magnesium-based vascular stents.In the present work we will give an overview of the recent progresses on biodegradable magnesium based vascular stents including magnesium alloy design,high-precision microtubes processing,stent shape optimisation and functional coating preparation.In particular,the Triune Principle in biodegradable magnesium alloy design is proposed based on our research experience,which requires three key aspects to be considered when designing new biodegradable magnesium alloys for vascular stents application,i.e.biocompatibility and biosafety,mechanical properties,and biodegradation.This review hopes to inspire the future studies on the design and development of biodegradable magnesium alloy-based vascular stents.