ZIF-8-based micro-arc oxidation composite coatings enhanced the corrosion resistance and superhydrophobicity of a Mg alloy

Mg alloys are considered the most promising engineering materials because of their unique properties.However,the uncontrolled corrosion rate of these alloys limits their applications.Therefore,in this study,a micro-arc oxidation layer was used as a transition layer to“directly”grow a zinc-based metal-organic framework(MOF)composite coating on the surface of a Mg alloy(AZ91D).Herein,the two zeolitic imidazolate framework(ZIF-8)coatings with different morphologies were separately prepared by homologous metal oxide induction and a one-step in-situ growth method.The superhydrophobic composite coating showed strong hydrophobicity and self-cleaning properties,which could prevent the penetration of water and corrosive ions(Cl^(−))into the surface of AZ91D.Electrochemical tests demonstrated that the super-hydrophobic composite coatings greatly enhanced the corrosion resistance of AZ91D,and the corrosion current density decreased from 10^(−5)to 10^(−9)A/cm^(2).These results indicate that the ZIF-8 coatings are beneficial for improving the hydrophobicity and enhancing the corrosion resistance of Mg alloys.Therefore,MOF composite coatings provide a new strategy that can be used to prepare multifunctional anticorrosion coatings on metal substrates.

Corrosion resistance and anti-soiling performance of micro-arc oxidation/graphene oxide/stearic acid superhydrophobic composite coating on magnesium alloys

Magnesium(Mg)alloys,the lightest metal construction material used in industry,play a vital role in future development.However,the poor corrosion resistance of Mg alloys in corrosion environments largely limits their potential wide applications.Therefore,a micro-arc oxidation/graphene oxide/stearic acid(MAO/GO/SA)superhydrophobic composite coating with superior corrosion resistance was fabricated on a Mg alloy AZ91D through micro-arc oxidation(MAO)technology,electrodeposition technique,and self-assembly technology.The composition and microstructure of the coating were characterized by scanning electron microscopy,X-ray diffraction,energy dispersive spectroscopy,and Raman spectroscopy.The effective protection of the MAO/GO/SA composite coating applied to a substrate was evaluated using potentiodynamic polarization,electrochemical impedance spectroscopy tests,and salt spray tests.The results showed that the MAO/GO/SA composite coating with a petal spherical structure had the best superhydrophobicity,and it attained a contact angle of 159.53°±2°.The MAO/GO/SA composite coating exhibited high resistance to corrosion,according to electrochemical and salt spray tests.

Understanding the corrosion and bio-corrosion behaviour of Magnesium composites – a critical review

Realising the potential of Magnesium(Mg),several globally leading ventures have invested in the Mg industry,but their relatively poor corrosion resistance is a never ending saga till date.The corrosion and bio-corrosion behaviour of Mg has gained research attention and still remains a hot topic in the application of automobile,aerospace and biomedical industries.The intrinsic high electrochemical nature of Mg limits their utilization in diverse application.This scenario has prompted the development of Mg composites with an aim to achieve superior corrosion and bio-corrosion resistance.The present review enlightens the influence of grain size(GS),secondary phase,texture,type of matrix and reinforcement on the corrosion and bio-corrosion behaviour of Mg composites.Firstly,the corrosion and bio-corrosion behaviour of Mg composites manufactured by primary and secondary processing routes are elucidated.Secondly,the comprehensive corrosion and bio-corrosion mechanisms of these Mg composites are proposed.Thirdly,the individual role of GS,texture and corrosive medium on corrosion and bio-corrosion behaviour of Mg composites are clarified and revealed.The challenges encountered,unanswered issues in this field are explained in detail and accordingly the scope for future research is framed.The review is presented from basic concrete background to advanced corrosion mechanisms with an aim of creating interest among the readers like students,researchers and industry experts from various research backgrounds.Indeed,the corrosion and bio-corrosion behaviour of Mg composites are critically reviewed for the first time to:(i)contribute to the body of knowledge,(ii)foster research and development,(iii)make breakthrough,and(iv)create life changing innovations in the field of Mg composite corrosion.

New superhydrophobic composite coatings on Mg-Mn-Ce magnesium alloy

A novel combined method for the formation of composite coatings on the Mg-Mn-Ce alloy is developed.Ceramic like matrix was formed on the Mg alloy surface by the plasma electrolytic oxidation.Then the samples were subsequently processed by dip-coating in an alcohol suspension of superdispersed polytetrafluoroethylene and spraying with the tetrafluoroethylene telomers solution.SEM,OSP,and SPM was used to study structure of formed surfaces.It was established by measurements of CA and CAH,as well as surface free energy calculations that formed coatings demonstrate superhydrophobic properties due to the presence of an irregular hierarchical surface structure and low surface free energy of fluoropolymers.The coating preserves its hydrophobic properties after exposure to high and low temperatures,for a long time as well as being in corrosive environments.EDS and XRD data analysis confirmed the presence of organofluorine compounds in the composite layers,including in the form of crystalline polytetrafluoroethylene.Using potentiodynamic polarization test and EIS,it was found that the resulting coatings significantly increase the corrosion resistance of Mg material.These data are also confirmed by salt spray tests for 40 days.Incorporation of fluoropolymers additionally decrease coatings coefficient of friction.

Surface metal-matrix composites based on AZ91 magnesium alloy via friction stir processing:A review

This monograph presents an overview of friction stir processing(FSP)of surface metal-matrix composites(MMCs)using the AZ91 magnesium alloy.The reported results in relation to various reinforcing particles,including silicon carbide(SiC),alumina(Al_(2)O_(3)),quartz(SiO_(2)),boron carbide(B_(4)C),titanium carbide(TiC),carbon fiber,hydroxyapatite(HA),in-situ formed phases,and hybrid reinforcements are summarized.AZ91 composite fabricating methods based on FSP are explained,including groove filling(grooving),drilled hole filling,sandwich method,stir casting followed by FSP,and formation of in-situ particles.The effects of introducing second-phase particles and FSP process parameters(e.g.,tool rotation rate,traverse speed,and the number of passes)on the microstructural modification,grain refinement,homogeneity in the distribution of particles,inhibition of grain growth,mechanical properties,strength–ductility trade-off,wear/tribological behavior,and corrosion resistance are discussed.Finally,useful suggestions for future work are proposed,including focusing on the superplasticity and superplastic forming,metal additive manufacturing processes based on friction stir engineering(such as additive friction stir deposition),direct FSP,stationary shoulder FSP,correlation of the dynamic recrystallization(DRX)grain size with the Zener–Hollomon parameter similar to hot deformation studies,process parameters(such as the particle volume fraction and external cooling),and common reinforcing phases such as zirconia(ZrO_(2))and carbon nanotubes(CNTs).

Corrosion behavior of composite coatings containing hydroxyapatite particles on Mg alloys by plasma electrolytic oxidation: A review

Mg and its alloys have been introduced as promising biodegradable materials for biomedical implant applications due to their excellent biocompatibility, mechanical behavior, and biodegradability. However, their susceptibility to rapid corrosion within the body poses a significant challenge and restricts their applications. To overcome this issue, various surface modification techniques have been developed to enhance the corrosion resistance and bioactivity of Mg-based implants. PEO is a potent technique for producing an oxide film on a surface that significantly minimizes the tendency to corrode. However, the inevitable defects due to discharges and poor biological activity during the coating process remain a concern. Therefore, adding suitable particles during the coating process is a suitable solution. Hydroxyapatite(HAp)has attracted much attention in the development of biomedical applications in the scientific community. HAp shows excellent biocompatibility due to its similarity in chemical composition to the mineral portion of bone. Therefore, its combination with Mg-based implants through PEO has shown significant improvements in their corrosion resistance and bioactivity. This review paper provides a comprehensive overview of the recent advances in the preparation, characterization, corrosion behavior and bioactivity applications of HAp particles on Mg-based implants by PEO.

Structure-function integrated magnesium alloys and their composites

Magnesium-based materials not only exhibit desirable characteristics such as low density and high specific strength, but also possess exceptional functional properties, including high damping capacity, high thermal conductivity, high electromagnetic interference shielding capacity, flame retardancy, and dissolvability. However, achieving a balance between strength and functional properties remains a significant challenge in Mg alloys community. Typically, strength depends on the pinning effect of defects, such as solute atoms and second phases,which hinder dislocation motion. On the other hand, optimal functional properties usually necessitate relative perfect crystal structures, as the presence of solute atoms and second phases can have adverse effects on damping capacity and thermal conductivity. Balancing these conflicting requirements is difficult. The trade-off between strength and functional properties of the Mg alloys should be broken to meet the urgent need in aerospace, automotive, 3C(computers, communications, and consumer electronics) and energy industries for high performance structural-functional integrated Mg-based materials. This review summarizes recent progress in understanding the mechanisms and influencing factors for the functional properties of Mg alloys. The mechanisms underlying the trade-off between strength and functional properties of Mg alloys is discussed. The latest developed structural-functional integrated Mg alloys and their composites are summarized, including high strength Mg-based materials with high damping capacity/high thermal conductivity/strong electromagnetic shielding capability/excellent flame-resistance/high dissolution rate. The future works of developing structure-function integrated Mg-based materials are proposed.

Development of 3D bicontinuous metal-intermetallic composites through subsequent alloying process after liquid metal dealloying

This study presents a novel process for the fabrication of metal-intermetallic composites with a 3D bicontinuous structure, achieved through a combination of liquid metal dealloying(LMD) and subsequent alloying. Initially, porous Ti structures are produced using the LMD process, followed by immersion in a molten Mg-3Al(wt%) metal. Due to the higher thermodynamic miscibility of Al with Ti compared to Mg, the concentration of Al in the Ti matrix increases as the immersion time increases. This results in a sequential phase transition within the Ti matrix: α-Ti → Ti_(3)Al → Ti Al. The phase transition considerably affects the hardness and strength of the composite material,with the Mg-Ti_(3)Al-Ti Al composite exhibiting a maximum hardness nearly twice as high as that of the conventional Mg-Ti composite. This innovative process holds potential for the development of various bicontinuous metal-intermetallic composites.

Selective interfacial bonding and thermal conductivity of diamond/Cu-alloy composites prepared by HPHT technique

Cu-based and Cu-alloy-based diamond composites were made by high-pressure-high-temperature （HPHT） sintering with the aim of maximizing the thermal conductivity of the composites. Improvements in interfacial bonding strength and thermo-physical properties of the composites were achieved using an atomized copper alloy with minor additions of Co, Cr, 13, and Ti. The thermal conductivity （TC） oh- mined exhibited as high as 688 W.m-1.K-1, but also as low as 325 W.m-1.K-l. A large variation in TC can be rationalized by the discrepancy of diamond-matrix interfacial bonding. It was found from fractography that preferential bonding between diamond and the Cu-alloy matrix occurred only on the diamond {100} faces. EDS analysis and Raman spectra suggested that selective interfacial bonding may be attributed to amorphous carbon increasing the wettability between diamond and the Cu-alloy matrix. Amorphous carbon was found to significantly affect the TC of the composite by interface modification.

Microstructure and mechanical properties of twin-wire arc sprayed Ni-Al composite coatings on 6061-T6 aluminum alloy sheet

We have systematically studied the microstructure and mechanical properties of Ni-5wt%Al and Ni-20wt%Al composite coat- ings fabricated on 6061-T6 aluminum alloy sheet by twin-wire arc spraying under different experimental conditions. The abrasive wear be- havior and interface diffusion behavior of the composite coatings were evaluated by dry/wet rubber wheel abrasive wear tests and heat treat- ment, respectively. Experimental results indicate that the composite coatings exhibit features of adhesive wear. Besides, the Vickers micro- hardness of NiA1 and Ni3AI intermetallic compounds is relatively larger than that of the substrate, which is beneficial for enhancing the wear resistance. With the increase of annealing temperature and time, the interface diffusion area between the Ni-Al coating and the substrate gradually expands with the formation of NiAl3 and Ni2Al3 phases, and is controlled by diffusion of aluminum atoms. The grain growth ex- ponent n of diffusion kinetics of the Ni-Al coating, calculated via a high-temperature diffusion model at 400, 480, and 550℃, is between 0.28 and 0.38. This satisfies the cubic law, which is consistent with the general theoretical relationship of high-temperature diffusion.

Electrochemical behaviors of Zn-Fe alloy and Zn-Fe-TiO_2 composite electrodeposition

Electrochemical behaviors of Zn-Fe alloy and Zn-Fe-TiO2 composite electrodeposition in alkaline zincatesolutions were studied respectively by the methods of linear potential sweep and cyclic voltammetry. From the re-sults it can be concluded that Zn shows under potential deposition, Zn-Fe alloy codeposition is anomalous codeposi-tion and Zn-Fe alloy cathode polarization is increased with the introduction of additive. From the view point of elec-trochemistry, the reasons that the content of Fe in the Zn-Fe coating changes with the composition of the electrolyteand the process conditions altering and the relationship between the content of Fe and the appearance of the coatingare interpreted. The cathode polarization of Zn-Fe alloy codeposition is enhanced obviously with addition of additive.In the course of composite electrodeposition, TiO2 has less promotion to electrodeposition of zinc ions than to iron i-ons, while the electrodeposition of iron ions improves the content of TiO2 in composite coating, which is inagreement with the results of process experiments.

Centrifugal casting processes of manufacturing in situ functionally gradient composite materials of Al-19Si-5Mg alloy

Cylindrical components of in situ functionally gradient composite materials of Al-19Si-5Mg alloy were manufactured by centrifugal casting. Microstructure characteristics of the manufactured components were observed and the effects of the used process factors on these characteristics were analyzed. The results of observations shows that, in thickness, the components possess microstructures accumulating lots of Mg2Si particles and a portion of primary silicon particles in the inner layer, a little MgzSi and primary silicon particles in the outer layer, and without any Mg2Si and primary silicon particle in the middle layer. The results of the analysis indicate that the rotation rate of centrifugal casting, mould temperature, and melt pouring temperature have evidently affected the accumulation of the second phase particles. Also, the higher the centrifugal rotation rate, mould temperature, and melt pouring temperature are, the more evident in the inner layer the degree of accumulation of Mg2Si and primary silicon particles is.

Influence of laser scanning speed on Cu-Zr-Al composite coatings on Mg alloys

To improve the surface properties of magnesium alloys, a study was conducted on Cu-Zr-A1 composite coatings on AZ91HP magnesium alloy by laser cladding. The influence of laser scanning speed on the microstructures and properties of the coatings was discussed. The coatings consist of amorphous phase, CusZr3, and Cul0ZrT. With the increase of laser scanning speed, the amorphous phase content of the coatings increases and reaches 60.56wt% with the laser scanning speed of 2.0 m/min. Because of the influence of laser scanning speed on the amorphous and crystal phases, the coatings show the maximum elastic modulus, hardness, and wear resistance at the laser scanning speed of 1.0 m/min. At the laser scanning speed of 2.0 m/min, the coatings have the best corrosion resistance.

Introduction to magnesium alloy processing technology and development of low-cost stir casting process for magnesium alloy and its composites

This paper presents the processing of magnesium alloys and its composite through different stir casting technologies.Design and devel-opment of stir casting technology that is suitable for processing of magnesium alloys has been done in this study.The low-cost stir casting processing of magnesium alloy and its composite with flux and without flux has been explained.The magnesium alloy and its composite have been fabricated by both the stir casting process.The micro structural characterization and mechanical properties of the developed composites has been evaluated.The optical emission spectroscopy of the developed alloy and factography of the developed alloy as well as composite was also examined.

Microstructure of Cu-based Amorphous Composite Coatings on AZ91D Magnesium Alloy by Laser Cladding

To improve the sliding wear resistance of AZ91D magnesium alloy, Cu-based amorphous composite coatings made of CuaTTi34Zr11Nis and Cu47Ti34Zr11Ni8＋20 wt pct SiC powders were fabricated on AZ91D magnesium alloy by laser cladding, respectively. SEM （scanning electron microscopy）, EDS （energy dispersive X-ray spectroscopy）, XRD （X-ray diffraction） and TEM （transmission electron microscopy） techniques were employed to study the phases of the coatings. The results show that the coatings mainly consist of amorphous phase and different intermetallic compounds. The reason of formation of amorphous phase and the function of SiC particles were explained in details.

Solute segregation in an Al_2O_(3f)/Al-4.5Cu alloy composite during solidification at different cooling rates

An Al_2O_(3f)/Al-4.5Cu composite was made by squeeze casting. The solutesegregation in the composite at different cooling rates was studied. The results indicate that theprimary crystal of Al-4.5Cu alloy nucleates and grows in the interstice between fibers. The fibersurface cannot serve as site for the heterogeneous nucleation of a primary dendrite. There exists anincreasing Cu concentration gradient from the center of the interstice between fibers to theinterface or the grain boundaries. There are the eutectic phases around the fibers. The solutesegregation in the matrix increases with the cooling rate rising. The amount of eutectic phasesfollowed by imbalance crystalline can be numerically calculated with Clyne-Kurz formula.

Preparation of WC/CoCrFeNiAl0.2 high-entropy-alloy composites by high-gravity combustion synthesis

The WC/CoCrFeNiAl0.2 high-entropy alloy(HEA)composites were prepared through high-gravity combustion synthesis.The preparation method is presented below.First,using a designed suitable multiphase thermite system,the molten CoCrFeNiAl0.2 HEA was fabricated using low-cost metal oxides.The molten HEA was subsequently infiltrated into the WC layer to fabricate WC/CoCrFeNiAl0.2 composites in a highgravity field.The porosity of the WC/CoCrFeNiAl0.2 composites was down-regulated,and their compressive yield strength was up-regulated when the high-gravity field was increased from 600g to 1500g because this infiltration process of a HEA melt into the WC layer is driven by centrifugal force.The WC particles in the composites exhibited a gradient distribution along the direction of the centrifugal force,which was attributed to the combined action of the high-gravity field and the temperature gradient field.The Vickers hardness of the sample was down-regulated from 9.53 to 7.41 GPa along the direction of the centrifugal force.

Insight of magnesium alloys and composites for orthopedic implant applications-a review

Magnesium(Mg)and its alloys have been widely researched for orthopedic applications recently.Mg alloys have stupendous advantages over the commercially available stainless steel,Co-Cr-Ni alloy and titanium implants.Till date,extensive mechanical,in-vitro and in-vivo studies have been done to improve the biomedical performance of Mg alloys through alloying,processing conditions,surface modification etc.This review comprehensively describes the strategies for improving the mechanical and degradation performance of Mg alloys through properly tailoring the composition of alloying elements,reinforcements and processing techniques.It also highlights the status and progress of research in to(i)the selection of nutrient elements for alloying,reinforcement and its effects(ii)type of Mg alloy system(binary,ternary and quaternary)and composites(iii)grain refinement for strengthening through severe plastic deformation techniques.Furthermore it also emphasizes on the importance of Mg composites with regard to hard tissue applications.

Corrosion resistance of composite coating on magnesium alloy using combined microarc oxidation and inorganic sealing

The combined microarc oxidation (MAO) and inorganic sealing process was used to deposit a composite coating to improve the corrosion resistance of AZ31 magnesium alloy.The surface morphologies of the resulting duplex coatings were studied by SEM.Furthermore,the corrosion resistance of the coated Mg alloy substrates was investigated using electrochemical workstation and dropping corrosion test.The results show that the composite coating surface consists of Mg,Si,O and Na.It is difficult to deposit inorganic coating on a thick MAO coating surface.As the composite coating was solidified by CO2 under 175 °C,it exhibits a better corrosion resistance than the MAO monolayer,owing to the thick and compact inorganic coating.

Application of novel sol-gel composites on magnesium alloy

Application o f defect-free,adherent,and corrosion protective sol-gel film on the magnesium alloys is generally difficult.In this study,two novel sol-gel/conversion coating composites were successfully deposited on AM60B magnesium alloy in order to provide sufficient protection against the corrosion.The first composite(Ti-Zr/hybrid)was obtained via combination o f a hybrid sol-gel film(synthesized by mixing tetraethoxysilane(TEOS),and 3-glycidyloxypropyl-trimethoxysilane(GPTMS))as outer layer and Ti-Zr conversion coating as primer.Also,the second composite(Ti-Zr/PTMS)was applied in a similar manner by combination o f phenyl-trimethoxysilane(PTMS)so lgel film with the Ti-Zr conversion coating.The morphology and elemental composition of the Ti-Zr conversion film were assessed by the Scanning Electron Microscopy(SEM)and Energy Dispersive X-ray Spectroscopy(EDS),respectively.A cracky conversion film was applied on the alloy surface after immersion in the Ti-Zr conversion coating bath which was mainly composed of MgO,T i02,Zr02,and MgF2 compounds.Uniform,but not-adherent PTMS and hybrid sol-gel films(pure sol-gel films)with obvious defects were directly deposited onto the magnesium alloy without the Ti-Zr pretreatment which were morphologically characterized by the SEM.However,formation o f relatively uniform and completely defect-free Ti-Zr/hybrid and Ti-Zr/PTMS composites after using the Ti-Zr conversion coating as pretreatment was revealed by the SEM observations.In addition,the defects of the Ti-Zr conversion coating were completely filled by the sol-gel layers.The Ti-Zr/PTMS and Ti-Zr/hybrid composite coatings were provided much better corrosion protection capacity than the pure PTMS and hybrid sol-gel films,respectively which was confirmed by the Electrochemical Impedance Spectroscopy(EIS)and Potentiodynamic Polarization(PDP)examinations in 0.05 M NaCl solution.