AZ31 Magnesium Alloy Substrates Research Articles

Improving the mechanical and wear properties of AZ91 magnesium alloy via laser cladded (AlCu)3.5CoCrNiSnx (x = 0 and 1) high entropy alloy coatings

(AlCu)3.5CoCrNiSnx (x = 0 and 1) high entropy alloy (HEA) coatings were prepared on AZ91 magnesium alloy substrate by laser cladding technology. Both the HEA coatings consisted of FCC phase and BCC phase. The addition of Sn could lead to an increase in the relative proportion of the BCC phase and the formation of coarse dendritic structure in the HEA coating. The average microhardness and average wear weight loss of the (AlCu)3.5CoCrNi coating (612.2 HV and 2.9 mg) and (AlCu)3.5CoCrNiSn coating (562.1 HV and 3.9 mg) were both higher and lower than those of the AZ91 substrate (70.5 HV and 5.5 mg), indicating that the prepared HEA coatings could significantly improve the properties of the substrate. The (AlCu)3.5CoCrNi coating showed better performance than the (AlCu)3.5CoCrNiSn coating due to the grain refinement effect.

Effect of microstructure and texture of AZ31 magnesium alloy substrate on nucleation and growth of biomimetic calcium phosphate coating

Magnesium has a special place in biomedical applications due to its biocompatibility and biodegradability properties. The high corrosion rate of magnesium in the body environment requires the use of a biocompatible coating such as calcium phosphate. In this paper, the effect of microstructure and crystalline texture of AZ31 magnesium alloy substrate on the morphology of calcium phosphate coating and the corrosion behavior of the material was investigated. The results imply that apatite crystals can form and grow on the surfaces of the biomimetic coating after soaking in simulated body fluid (SBF). The corrosion behavior of the material was investigated using an electrochemical polarization test in SBF solution for 3 days. The results showed that changes in the microstructure and crystalline texture of the substrate changed the coating morphology so that the growth of calcium phosphate changed from a rod-shaped with a diameter of 100–150 nm to a blade-shaped with a thickness of 20–50 nm. An increase in the corrosion resistance of the coated specimens with the corrosion rate of 0.65 mm/year was obtained compared to the uncoated specimen with the corrosion rate of 2.62 mm/year.

Microstructure and anti-corrosion properties of acrylic bone cement-based with MOF nanostructured hybrid coatings on AZ31 Mg alloy

Surface modification of biomedical AZ31 magnesium (Mg) alloy substrates with biocompatible and applicable polymer coatings is an effective and simple method to improve corrosion resistance. Herein, the biodegradable acrylic bone cement incorporation with different content of metal organic frameworks (Ce-MOFs or Zn-MOFs) coated on biodegradable Mg alloy (AZ31) substrates was fabricated by using a dip-coating method. Then, various characterizations like X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) and the water contact angle (WCA) tests were performed to determine the composition, morphology, structure, and wettability of the coatings. The compact acrylic bone cement coatings improve the hydrophilic effect due to the micro/nanostructure of acrylic and hydrophilic groups, but the addition of a small amount of Ce-MOF and Zn-MOFs structures reduces the hydrophilic effect of the coating surface. According to the electro-chemical analysis, prepared acrylic coating has better corrosion behavior compared to AZ31 sample. The PM sample demonstrates the lowest corrosion current density (icorr = 0.095 mA cm−2) compared to other samples. The dense acrylic compact coatings with higher amount of Ce-MOF content blocks the pores in the coating and lead to an inhibitory effect and improved the corrosion behaviors. The dense acrylic bone cement containing MOF coatings with improved electrochemical activity inhibits diffusion of the aggressive ions to the alloy surface.

Discharge Characteristics, Plasma Electrolytic Oxidation Mechanism and Properties of ZrO2 Membranes in K2ZrF6 Electrolyte.

ZrO2 was coated on AZ31 magnesium alloy substrate by plasma electrolytic oxidation with K2ZrF6 and NaH2PO4 electrolytes. The discharge characteristics and variation in active species during the plasma electrolytic oxidation (PEO) process were studied by optical emission spectroscopy. The surface morphology and element composition of the membranes were observed by scanning electron microscope. The ion transfer of the substrate was studied by atomic absorption spectroscopy. The phase composition and corrosion characteristics of the PEO membranes were examined with XRD and an electrochemical workstation, respectively. The heat and mass transfer models during the PEO process were introduced. The contributions of ions to the membranes and active species were also analyzed. The results indicated that the ion transfer at different stages exhibits different tendencies. At the first and transition stages, the migration resistance of the ions was low and increased gradually. At the initial discharge stage, the migration resistance was the highest because the highest membrane growth rate occurred at this stage. At the later discharge stage, the migration resistance tends to be stable, which is ascribed to a dynamic equilibrium PEO membrane growth rate. The intensity of active species is related to the energy state of the working electrode’s surface. The higher the energy, the greater the probability that the active species will be excited to generate energy level transitions, and the higher the plasma concentration.

Corrosion Evolution of AZ31 Mg Alloy with a Nano Crystallized Film

A comprehensive investigation of nano crystallized GaN film synthesized on AZ31 magnesium alloy substrate using atomic layer deposition (ALD) is presented in this paper. The microstructure and mechanical analysis indicate the nano crystallized film is homogeneous, well-adhesive to Mg alloy substrate. The corrosion experimental results demonstrate that the nanometer crystallized film turns Mg alloy corrosion process from longitudinal/non-uniform to horizontal/uniform corrosion, which is deduced from the facts that a great but less fluctuation surface potential mapping, a smaller ∆Erev, corr and a more uniformed corroded morphology. A higher Ecorr , a smaller icorr and a higher Z also mean the film can yield a prominent amelioration in the Mg alloy corrosion resistance. The work proposes that a uniform coverage even in a nano-magnitude and crystallized form could make corrosion more uniform and later.

Comparative Analysis of Mechanical Properties of WC-based Cermet Coatings Sprayed by HVOF onto AZ31 Magnesium Alloy Substrates

Comparative Analysis of Mechanical Properties of WC-based Cermet Coatings Sprayed by HVOF onto AZ31 Magnesium Alloy Substrates

Al–AlN composite coatings on AZ31 magnesium alloy for surface hardening and corrosion resistance

Al–AlN composite coatings were prepared using filtered cathodic vacuum arc deposition on AZ31 magnesium alloy substrates. With increasing substrate bias, AlN phase content increased and Al phase content decreased, resulting in increased hardness of the coatings. Transmission electron microscopy morphology of the composite coatings at 100 V bias showed that the metallic Al phase was embedded in the AlN matrix. The coatings significantly enhanced the corrosion resistance of the AZ31 magnesium alloy. The maximum hardness was 512 HV obtained at a bias of 300 V and a minimum corrosion current density was 1.913 × 10−6 A/cm2 attained at a bias of 100 V. The effect of substrate bias on microstructure, coating thickness, and residual stress in the coatings was studied in details.

Corrosion resistance of Mg−Al LDH/Mg(OH)2/silane−Ce hybrid coating on magnesium alloy AZ31

Abstract An environmentally-friendly hybrid coating on AZ31 magnesium alloy substrates was reported. The synergic effect was studied on Mg−Al-layered double hydroxide Mg−Al LDH/Mg(OH)2-coated AZ31 magnesium alloy via an in-situ steam coating process and a subsequent combined surface modification of bis-[triethoxysilylpropyl]tetrasulfide (BTESPT) silane and Ce(NO3)3. The microstructure and composition characteristics of the hybrid coatings were investigated by means of X-ray diffraction (XRD), scanning electronic microscopy (SEM), Fourier transform infrared spectrophotometry (FT-IR) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the coated samples was evaluated by potentiodynamic polarization (PDP), electrochemical impedance spectrum (EIS) and hydrogen evolution rate during immersion in 3.5 wt.% NaCl solution. The results show an improved corrosion resistance of the alloy in the presence of BTESPT silane and Ce(NO3)3. This is most likely due to the synergistic effect of steam coating and silane coating to enhance the barrier properties of hybrid coating. In addition, the formation mechanism and anti-corrosion mechanism of coatings were discussed.

Tribological behavior of AZ31/ZrO2 surface nanocomposites developed by friction stir processing

Abstract The present study focused on the poor wear resistance of the AZ31 magnesium alloy and improving its tribological applications. Surface nanocomposites reinforced with nano-sized ZrO2 particles on the AZ31 magnesium alloy substrate were fabricated by friction stir processing (FSP) in two different pass number. The average grain size of the as-received AZ31 base metal reduced from 11 μm to 2 μm in the case of AZ31/ZrO2 surface nanocomposite developed by four passes of FSP. Secondary electron microscopy (SEM) images of the 4-pass FSPed nanocomposite showed that the ZrO2 nanoparticles distributed homogenously in the magnesium matrix. Microhardness measurements revealed a significant improvement by adding ZrO2 nanoparticles and also increasing in FSP pass number. The microhardness of the AZ31 base metal improved about 90% in the case of four passes FSPed AZ31/ZrO2 surface nanocomposite. The wear performance of the samples was evaluated using a reciprocal wear machine and AISI 52100 steel with the hardness of 63 HRC as the counterpart. Investigating the wear performance and friction coefficient of the samples revealed enhanced tribological behavior in FSPed samples. The wear rate of the AZ31 base metal reduced about 40% for the 4-pass FSPed AZ31/ZrO2 nanocomposite. The average friction coefficient of the 4-pass FSPed nanocomposites was about half of the base metal. The SEM observations of the worn surface, wear track cross-section, counterpart tip and wear debris indicated that the wear mechanism changed from severe abrasion and adhesion for AZ31 base metal to mild abrasion for the 4-pass FSPed AZ31/ZrO2 nanocomposite.

Investigation of strain-hardening characteristics of cold-sprayed Al–Al2O3 coatings: a combined nanoindentation and expanding cavity models approach

ABSTRACT The paper has taken a fundamental approach to study the nano-scale deformation behavior of Al-Al2O3 cermet coatings deposited by low-pressure cold spraying (LPCS) on AZ31 magnesium and Al6056 lightweight alloy substrates. Coating microstructural characteristics were first evaluated and correlated with LPCS process parameters using metallurgical characterization techniques: SEM, 3D optical profilometry, and XRD, followed by their microhardness and wear depth measurements and comparing with uncoated substrates under three-body abrasion wear. These properties were analyzed/mapped against probable deformation scenarios for nano-scale yield strength determination using the combined experimental nanoindentation load-depth curve method and computational expanding cavity models (ECMs). Obtained yield strength with key coating parameters like hardness and Young’s modulus were taken for modeling and simulation of strain-hardening effect under a peak loading of 165 mN in ABAQUS finite element (FE). Results from both combined experimental/computational and FE approaches indicate a progressive elasto-plastic mode being the dominating coating deformation mechanism with a strain hardening exponent of 0.15, under the studied loads.

Control of magnesium alloy corrosion by bioactive calcium phosphate coating: Implications for resorbable orthopaedic implants

Control of the corrosion that occurs in magnesium alloys in vivo is a significant challenge for their use as resorbable orthopaedic implants. In this work, we report on the provision of bioactive calcium phosphate (CaP) coatings on magnesium alloys that can delay substrate corrosion while offering an attendant physiochemical environment with properties known to promote an osteoinductive response in vivo. RF magnetron sputtering from hydroxyapatite (HA) powder targets has been employed to create CaP coatings on AZ31 magnesium alloy substrates. Coatings of ∼70 and 210 nm thickness were achieved via regulation of sputtering parameters, in particular deposition time. XPS and ToF-SIMS were used to investigate the chemistry of the coating alloy interface and also to confirm composition and thickness. The Ca/P atomic ratio of the coatings was determined by EDX to be 1.54. µCT analysis showed a substrate volume loss after 14 days exposure to SBF of 5.89 ± 3.15 mm3 for the un-coated alloy while the presence of the ∼70 nm CaP coating reduced this to 3.42 ± 0.48 mm3 and the ∼210 nm coating to 0.30 ± 0.28 mm3. The corrosion rates were calculated to be 1.74 ± 0.06 mmpy for the AZ31 control; 1.57 ± 0.09 mmpy for the ∼70 nm CaP coated alloy and 1.01 ± 0.07 mmpy for the ∼210 nm CaP coating. This data confirms that CaP coating thickness can control the rate of corrosion of magnesium alloys while offering the potential for improved bioactivity.

Microstructural characteristics of chitosan deposited az91 magnesium alloy

Magnesium (Mg) and its alloys have been extensively explored as potential temporary implant materials for orthopaedic applications (e.g. Fracture fixation). Magnesium alloy (AZ91) is used for bone implant application since it has lightest structural element, biocompatible, osteoconductive and its mechanical properties are similar to bone. However, they are prone to corrosion in the human body. Hence in order to reduce the corrosion rate and enhance the biocompatibility and biological properties, AZ91 magnesium alloy surface is modified with chitosan layers. Chitosan coating is proposed to decrease the corrosion rate and improve the bioactivity of AZ91 magnesium alloy. In the study, chitosan was coated on the surface of AZ91 magnesium alloy by spin coating technique. The presence of functional group bands of chitosan coating was confirmed using Fourier transform infrared spectroscopy (FTIR).The surface morphology and the grain size of chitosan on AZ91 magnesium alloy substrate was investigated using Field emission scanning electron microscope (FESEM) analysis. The elemental composition of chitosan was confirmed by Energy dispersive X-ray spectroscopy (EDAX) study. The film thickness was also measured for the coated substrate. Thus chitosan is coated on AZ91 magnesium alloy and characterization are done to confirm the presence of chitosan on AZ91 magnesium substrate which can be further tested for its biocompatible properties and used for orthopaedic applications.

Corrosion resistance of a ceria/polymethyltrimethoxysilane modified Mg-Al-layered double hydroxide on AZ31 magnesium alloy

A Mg-Al-layered double hydroxide (LDH) coating modified with methyltrimethoxysilane (MTMS) and cerium nitrate was prepared on AZ31 magnesium alloy substrate via a hydrothermal process and subsequent the immersion treatment. The surface morphologies and chemical compositions were investigated using FE-SEM, XRD, FT-IR and XPS. These results indicated that the composite coatings were consisted of polymethyltrimethoxysilane (PMTMS) and CeO2. The adherence between the PMTMS/CeO2 coating and the LDH coating was significantly improved with the formation of Si-O-Si and Si-O-Mg chemical bonds. Electrochemical tests and hydrogen evolution illustrated that the optimum corrosion resistance of the composite coating was obtained in presence of 10−3 mol/L cerium nitrate. In addition, experimental data proved that addition of an excess of cerium nitrate was bad for coating formation. Finally, the coating corrosion mechanism was proposed and discussed.

Anti-corrosion performances of hybrid silane coatings on AZ31 alloy

Purpose This paper aims to evaluate the efficacy of a zeolite-filled silane sol–gel coating as protective layer on pretreated AZ31 magnesium alloy substrates. Design/methodology/approach Anti-corrosion properties of a silane–zeolite composite coating, at various zeolite content, have been investigated on AZ31 magnesium substrates subjected to different surface pretreatment procedures before coating deposition. A short time etching by hydrofluoric acid (HF) and an anodic polarization in NaOH solution were used as surface pretreatments. Findings High hydrophobicity and good adhesion performances of coatings have been observed. Corrosion protection performance, during immersion in 3.5 per cent NaCl solution, was evaluated by means of electrochemical impedance spectroscopy tests. All coating formulations evidenced good barrier properties. Better durability properties have been shown by coating obtained on HF pretreated magnesium substrate and with a 60 per cent of zeolite content. Originality/value High electrochemical reactivity of magnesium alloys represents the mayor limit of its application in many different fields. In this concern, zeolite-based coatings are emerging as potentially effective environmentally friendly coating for metallic substrates. Despite aluminum and stainless steel substrates, in the literature, only expensive direct synthesis zeolite coating was investigated for its application on magnesium alloys protection. For this reason, this paper fulfills the need to assess the adhesion and anti-corrosion behavior of sol–gel silane–zeolite coating in magnesium alloy substrates.

Influence of Aliquat 336 on tribological properties of electroless ternary nanocomposite coatings on AZ91 alloy

Incorporation of fine nanoparticles and cationic surfactant (Aliquat 336) within an ENi–P matrix has given a new dimension to the field of nanocomposite coatings. It describes the surface engineering processes currently used for the protection of AZ91 magnesium alloy surface against wear, including electroless nano-composite coatings. The present work aims to investigate the influence of Aliquat 336 cationic surfactant on the microhardness and tribological properties of electroless (Ni–P–ZnO) ternary alloy nanocomposite coatings on AZ91 magnesium alloy substrate from acidic bath. The results revealed that there was a significant improvement in the microhardness and wear resistance of the coated surface by the addition of cationic surfactant at a concentration of 1.5 g/L as compared to the coating obtained without the addition of cationic surfactant in the chemical bath. These results are thus clearly indicative of the fact that the component of life of members made from substrate subjected to nanocomposite coatings with varying the concentration of surfactant can be greatly improved, thereby preventing early or regular failures, and increasing service life.

Effect of lanthanum nitrate on the microstructure and electrochemical behavior of PEO coatings on AZ31 Mg alloy

Plasma electrolytic oxidation coating was carried out in phosphate-based electrolyte embedded with different amounts of lanthanum nitrate (LN) on AZ31 magnesium alloy substrate in order to characterize the microstructure and protective properties of the prepared coatings. The SEM/elemental map results show that the additive lanthanum is positioning homogeneous within coating structure. Also, according to the obtained results and mechanism of PEO coating formation, the amount of additive replacement within the external porous layer was more than the replacement occurred within the internal dense structure. Results of potentiodynamic polarization (PDS) and electrochemical impedance spectroscopy (EIS) tests show that the corrosion resistance properties of PEO coatings in the presence of LN additives are greatly improved. Formation a structure with a higher density coupled with the barrier role of deposited lanthanum hydroxide due to the penetration of corrosion agents improves the corrosion resistance of the oxide coating. Finally, thermodynamic calculations prove that lanthanum hydroxide sediments were formed in respective immersion condition and also shows their stability and insolubility.

Preparation and corrosion resistance of magnesium phytic acid/hydroxyapatite composite coatings on biodegradable AZ31 magnesium alloy.

In this work, a magnesium phytic acid/hydroxyapatite composite coating was successfully prepared on AZ31 magnesium alloy substrate by chemical conversion deposition technology with the aim of improving its corrosion resistance and bioactivity. The influence of hydroxyapatite (HA) content on the microstructure and corrosion resistance of the coatings was investigated. The results showed that with the increase of HA content in phytic acid solution, the cracks on the surface of the coatings gradually reduced, which subsequently improved the corrosion resistance of these coated magnesium alloy. Electrochemical measurements in simulated body fluid (SBF) revealed that the composite coating with 45 wt.% HA addition exhibited superior surface integrity and significantly improved corrosion resistance compared with the single phytic acid conversion coating. The results of the immersion test in SBF showed that the composite coating could provide more effective protection for magnesium alloy substrate than that of the single phytic acid coating and showed good bioactivity. Magnesium phytic acid/hydroxyapatite composite, with the desired bioactivity, can be synthesized through chemical conversion deposition technology as protective coatings for surface modification of the biodegradable magnesium alloy implants. The design idea of the new type of biomaterial is belong to the concept of "third generation biomaterial". Corrosion behavior and bioactivity of coated magnesium alloy are the key issues during implantation. In this study, preparation and corrosion behavior of magnesium phytic acid/hydroxyapatite composite coatings on magnesium alloy were studied. The basic findings and significance of this paper are as follows: 1. A novel environmentally friendly, homogenous and crack-free magnesium phytic acid/hydroxyapatite composite coating was fabricated on AZ31 magnesium alloy via chemical conversion deposition technology with the aim of enhancing its corrosion resistance and bioactivity. The chemical conversion coatings, which are formed through the reaction between the substrate and the environment, have attracted increasing attention owing to the relative low treatment temperature, favorable bonding to substrate and simple implementation process. 2. With the increasing of hydroxyapatite (HA) content, the crack width in the composite coatings and the thickness of the coatings exhibit obviously decreased. The reason is probably that when adding HA into the phytic acid solution, the amount of active hydroxyl groups in the phytic acid are reduced via forming the coordination bond between P-OH groups from phytic acid and P-OH groups from the surface of HA, thus decreasing the coating thickness and hydrogen formation, as well as avoiding coating cracking. 3. By adjusting the HA content to 45 wt.%, a dense and relatively smooth composite coating with ~1.4 μm thickness is obtained on magnesium alloy, and exhibits high corrosion resistance and good bioactivity when compared with the single phytic acid conversion coating.

Preparation and properties of plasma sprayed NiAl10 and NiAl40 coatings on AZ91 substrate

Magnesium alloys are, due to high specific strength and stiffness, materials suitable for lightweight applications in automotive and aeronautical industries. Very poor corrosion resistance of magnesium and magnesium alloys significantly limits their wide utilization. Magnesium alloys are very susceptible to galvanic corrosion that can result in serious pitting corrosion, particularly in wet and salty environment. Magnesium and its alloys can be protected by formation of protective surface layers which can be achieved by plasma spraying capable of preparing metal and/or ceramic coatings. In this work, plasma coatings of NiAl10 and NiAl40 on AZ91 magnesium alloy substrate were prepared by the hybrid plasma spraying system WSP®-H 500. Present results show a significant effect of the preheat temperature of the AZ91 substrate during plasma spraying on development of a diffusion bonding due to the formation of sub-layer composed of Mg3AlNi2, Al12Mg17 phases and of Mg and Al solid solutions. The plasma sprayed coatings were observed by scanning electron microscope with elements point analysis and by X-ray phase analysis. The mechanical properties of prepared coatings were evaluated by adhesion tests. The corrosion resistance of prepared coatings was evaluated using the method of potentiodynamic measurements performed in the 0.5mol·l−1 NaCl solution while the long-term corrosion resistance was assessed in condensation chamber in wet air atmosphere at the temperature of 35°C. Both the tests showed significant effect of present sub-layers on resulting corrosion resistance.

Surface Properties Contrast between Al Films and TiO2 Films Coated on Magnesium Alloys by Magnetron Sputtering

Al films and TiO2 films were separately coated on AZ31 magnesium alloy substrates by means of magnetron sputtering method. The surface properties of the samples were explored and compared. Scanning electron microscope (SEM) observed the compact structure characteristics of as-deposited Al films and TiO2 films. After heat treatment under 200oC for half an hour the films kept the compact structure characteristics and there didn’t exist structural defects on the surface of the films. Nano-indentation measurement results display that the micro-hardness of as-deposited Al film and TiO2 film reaches about 1.90 Gpa and 1.51 Gpa, separately. Al film is a bit harder than TiO2 film. Finally, the corrosion experiments in simulated body fluid initially indicate the different corrosion properties for Al film and TiO2 film. Al film presents more effective anti-corrosion properties than TiO2 film.

Structural and corrosion characterization of hydroxyapatite/zirconium nitride-coated AZ91 magnesium alloy by ion beam sputtering

The adhesion of hydroxyapatite (HA) as a coating for the AZ91 magnesium alloy substrate can be improved by using the sputtering method and an intermediate layer, such as ZrN. In this study, HA coatings were applied on ZrN intermediate layers at a temperature of 300°C for 180, 240, 300, 360, and 420min by ion beam sputtering. A profilometer device was used to study the HA coating thickness, which changed from 2μm for the 180-min deposition to 4.7μm for 420-min deposition. The grazing incidence X-ray diffraction analysis method and the Williamson–Hall analysis were used for structural investigation. As the deposition time increased, the crystalline size increased from 50nm to 690nm. However, given sufficient time for stress relief on the coating structure, the lattice strain values were close to zero. Energy-dispersive X-ray spectroscopy results showed that the Ca/P ratio ranged from 1.73 to 1.81. The external indentation method was used to evaluate the coating adhesion to the substrate. The slope of curve for applied force changes versus the radius of cracks in the coating (dP/dr) varied in the range of 0.2–0.07 by the deposition time, indicating that the adhesion increased with the increase in coating thickness. The potentiodynamic polarization technique was used to study the corrosion behavior. With increasing deposition time, the corrosion potential of samples did not show a significant change, and the corrosion potential of all samples (coated and uncoated substrates) was more positive than approximately 55mV. When the deposition time increased to 360min, the corrosion current density decreased from 5.5μA/cm2 to 0.33μA/cm2. After 420min of deposition, the current density increased to 8.2μA/cm2. Scanning electron microscopy images of the HA surface layer after 420min clearly showed cracks on the coating surface, which led to the increase in corrosion current density.