MgZn2 Phase Research Articles

Effects of Ag, Cu or Fe addition on microstructure and comprehensive properties of biodegradable Zn-Mg alloy

In recent years, Zn-0.5 wt%Mg alloys have drawn a lot of attention as a potential candidate in biodegradable implant applications as it demonstrated more corrosion resistant property in comparison to Fe- and Mg-based alloys. Zn-0.5 wt%Mg based alloys were fabricated through powder metallurgy. This work examined the impact of the micro-alloying metals Cu, Fe, and Ag on Zn-Mg alloys. Moreover, the structure, absorbing properties, morphology, electrochemical properties, electrical properties, and wettability were also investigated. All fabricated Zn-0.5 wt%Mg alloys formed a primary phase of Mg2Zn11 and secondary phase of MgZn2. A minor phase of Zn was also identified in XRD analysis. Optical analysis showed that the Zn-0.5 wt%Mg-0.2 wt%Cu alloy gave a strong peak of absorbance at a short wavelength of 230 nm which is due to its colour. All alloys sintered at 350 ◦C displayed micro-needles having size in the range of 1.82–26.2 µm in SEM analysis. Zn-0.5 wt% Mg-0.2 wt% Cu alloy offered 140 Hv value of Vickers hardness. The electrochemical test findings measured corrosion resistance and most corrosion resistant material was Zn-0.5 wt%Mg-0.2 wt%Cu alloy with corrosion rate 0.0120 mm/year. Zn-0.5 wt%Mg-0.2 wt%Cu offered the conductivity with the least value of 7.45 ×10−12 Ω−1m−1and highest value of resistivity at 1.335 ×1011Ω-m, based on electrochemical study. All fabricated biodegradable Zn-0.5 wt%Mg alloys had an angle less than 90, indicating hydrophilicity as determined by wettability studies. Zn-0.5 wt%Mg-0.2 wt%Cu is the most suitable alloy in cardiovascular stent and orthopaedic implant applications.

Corrosion behavior of erbium modified Zn-11Al-3Mg cast alloy in stagnant 3.5 wt% NaCl solution

Zn-11Al and Zn-11Al-3Mg-xEr (x=0, 0.05, 0.1, 0.5) alloys were prepared, and the microstructures and corrosion resistance of the alloys were investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD), and electrochemical methods. The results show that the primary Al-rich phase in Zn-11Al alloys is corroded as the main anode. The electronegativity of the primary Al phase in Zn-11Al-3Mg alloys is higher than the primary MgZn2 phase, and the electronegativity of Al-rich and Mg2Zn11 phases is higher than that of the η-Zn phase in ternary eutectic structure. The primary Al-rich phase and Mg2Zn11 phases in the alloy are corroded as the main anodes. On the other hand, the erbium (Er) reacts with Al to form the AlEr phase, and the AlEr phase has a significant refining and homogenizing effect on the primary Al-rich phase in the Zn-11Al-3Mg alloy. When the content of Er is 0.05%, the primary Al phase transforms into fine discontinuous cellular structure. However, the increase of Er addition promotes the growth of primary Al-rich phase and the reduction of ternary eutectic, which weakens the corrosion resistance of the alloy.

Effect of Ce on microstructure and dynamic compression properties of ZK60 alloy

The Mg–6Zn– xCe–0.6Zr ( x = 1, 2) alloys were subjected to a dynamic compression experiment, and the change in microstructure was noticed and studied. The primary components of two alloys are α-Mg matrix, Mg7Zn3 phase, and (Mg1− xZn x)11Ce phase. The two alloys have grain diameters of 2.8 and 3.2 μm, respectively. The dynamic compressive mechanical characteristics of the two alloys show a positive strain-strengthening effect, with Mg–6Zn–1Ce–0.6Zr alloy having somewhat higher values than Mg–6Zn–2Ce–0.6Zr alloy. At a strain rate of 500 s−1, {10[Formula: see text]2} tensile twin is the dominant deformation mechanism for two alloys, but the Mg–6Zn–2Ce–0.6Zr alloy is more prone to produce {10[Formula: see text]2} tensile twin. With the increase of the strain rate, the dominant deformation mechanism changes from {10[Formula: see text]2} tensile twin to pyramidal slip.

Cryo-compression and annealing hardening of 7075 aluminum alloy

7075 aluminum alloy, as a lightweight, high-strength, and corrosion-resistant structural material, is widely used in the aviation industry. Because 7075 aluminum alloy is commonly used in structural components, its plastic processing ability is highly required by the usage environment. Recent studies have shown that 7075 aluminum alloy exhibits better deformation ability under low temperature conditions. In this paper Cryo-compression experiments on 7075 aluminum alloy under different compression rates (0.001 s-1-0.5 s-1) in a low-temperature environment (soaked in liquid nitrogen for 30 minutes) has been discussed. Annealing process research was conducted on the low-temperature compressed samples, and the optimal annealing process parameters (400Co, insulation for 15 minutes) and optimal deformation amount (16%) were obtained through comparison of microstructure and properties. And it was found that 7075 aluminum alloy exhibited annealing hardening phenomenon when annealed at 250 Co, and the reason was the diffusion segregation of solid solution elements formed during low-temperature forming, which led to the precipitation of the second phase MgZn2 during low-temperature annealing.

Microstructure Observation of Al-Zn-Mg Alloy with High Mg Content

The microstructure and mechanical properties of Al-Zn-Mg alloys with low Zn/Mg ratios have been studied.According to various researchers, the major strengthening is due to η-phase and T phase. There are many briefly research on the microstructure and interface of the η-phase types but not briefly information about the T-phase That’s why now our aim to work on T-phase. In actual our aim is to observe the T-phase interface. The MgZn2 phase (η phase) and its metastable phase (η′ phase) were the most prominent precipitates. Another study revealed various Mg32(Al,Zn)49 phases (T phase) and their metastable phase (T′ phase) in Al-Zn-Mg alloys with low Zn and high Mg content. Al-Zn-Mg alloys with a Zn/Mg ratio of 0.71 were explored for this study. The alloy with a Zn/Mg ratio of 0.71 aged at 473k for 2000 minutes exhibited the highest hardness, according to the observations. The strengthening precipitates in the investigated alloy were totally T′ phase, according to TEM observation.

Effect of extrusion temperature on the microstructure and mechanical properties of hot-extruded ZK60 magnesium alloy

ZK60 magnesium alloy was prepared by the hot-pressed sintering combined with the hot-extruded technique. The microstructure and mechanical properties evolution of ZK60 alloy with a reduced extrusion temperature from 350 °C to 250 °C were investigated in detailed. The extruded alloy was mainly composed of fine α-Mg grains and MgZn2 phase. The grains size gradually decreased with a reduction in extrusion temperature, and the yield strength obviously increased accordingly. The alloy extruded at 250 °C exhibited the smallest average grain size of 2.5 μm and the best combination of strength and plasticity, with a yield strength of 279 MPa and fracture strain of 18.1% in compressive condition, and 263 MPa and 13.7% in tensile condition, as well as a tension-compression yield asymmetry of 0.94. Both the fine grains formed by the continuous and twin induced dynamic crystallization mechanism and the precipitation strengthening contributed to the strength improvement.

Effects of solution temperatures on microstructures and mechanical properties of B4C/7A04Al composites: A comparison study with 7A04Al alloys

To prepare particle-reinforced aluminum matrix composites with ultra-high strength, high-strength 7xxx Al alloys are commonly employed as matrices. Heat treatment plays a crucial role in enhancing the mechanical properties of the alloys and their composites, but the influence of solution temperatures on composites based on 7xxxAl alloys remains unexplored. In this study, the effects of solution temperatures on the microstructures and mechanical properties of B4C/7A04Al composites fabricated via powder metallurgy (PM) technology were investigated, as well as those of 7A04Al alloys for comparison. Before solution treatments, the prominent second phases in the composite were MgZn2 phases, while those in the 7A04Al alloy consisted of MgZn2 and Al2CuMg phases. At lower solution temperature (420 °C), MgZn2 phases dissolved completely, whereas Al2CuMg phases persisted. Al2CuMg phases dissolved at 450 °C, and thus the 7A04Al alloy obtained the optimum strength and elongation. Further elevating the solution temperature caused abnormal grain growth (AGG) in the 7A04Al alloy, leading to a deterioration of strength and plasticity. In contrast, at various solution temperatures, the composite exhibited stability in grain size, which could be attributed to the pinning effects of B4C particles and Mg(Al)B2 phases, the reaction products between the boron impurity and the Al matrix. However, at higher solution temperatures (510 °C and 600 °C), the segregation of Mg and O around B4C particles was aggravated, and thus the elongation of the composite deteriorated. Interestingly, the strength remained relatively unaffected due to the strengthening effects of Mg(Al)B2 phases. The results indicate that the composite exhibited a broad range of solution temperature with comparable strength and elongation across a temperature range of 420 °C–470 °C. But for the 7A04Al alloy, the optimal solution temperature is 450 °C.

Mechanical Properties, Degradation Behavior, and Cytocompatibility of Zn–Mg–Graphene Nanoplatelets Composite for Orthopedic‐Implant Applications

Zinc (Zn)‐based materials reveal inadequate mechanical properties as orthopedic biodegradable implantable materials, which limits their biomedical applications. Herein, Zn–xMg (magnesium) composites (x = 0.5, 1.0, 1.5, and 2.0 wt%) reinforced with 0.2 wt% graphene nanoplatelets (GNP) are obtained via powder metallurgy and hot‐pressing sintering. The addition of 0.5–2.0 wt% Mg into Zn–0.2 wt% GNP composite resulted in the formation of Mg2Zn11 and MgZn2 phases without any additional intermetallic carbide phases. The hot‐pressing sintered (HPS) Zn–0.5Mg–0.2GNP composite exhibits a compressive yield strength of 169 ± 18 MPa, an ultimate compressive strength of 270 ± 39 MPa, a compressive strain of 17 ± 6%, and a microhardness of 86 ± 2 HV. Electrochemical corrosion testing reveals that corrosion resistance of HPS Zn–xMg–0.2GNP composites decreases with increasing Mg content, while immersion tests in Hanks’ balanced salt solution for 30 d indicate that the degradation rate increases from 0.032 to 0.141 mm y−1 by increasing Mg content from 0 to 2.0 wt%. In vitro cytotoxicity assessments using SaOS2 human osteoblast cells show >90% viability following exposure over 5 d to 12.5% extract concentrations of all HPS composites. The HPS Zn–0.5Mg–0.2GNP composite exhibits the appropriate material properties for biodegradable bone‐implant applications.

Study on the Microstructure of Mg-4Zn-4Sn-1Mn-xAl As-Cast Alloys.

In this study, the microstructure of the Mg-4Zn-4Sn-1Mn-xAl (x = 0, 0.3 wt.%, denoted as ZTM441 and ZTM441-0.3Al) as-cast alloys was investigated using scanning electron microscopy (SEM), focused-ion/electron-beam (FIB) micromachining, transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The analysis results revealed that the microstructure of the ZTM441 and ZTM441-0.3Al as-cast alloys both mainly consist of the α-Mg matrix, skeleton-shaped MgZn2 eutectic texture, block-shaped Mg2Sn, and Zn/Sn-rich nanoscale precipitate bands along the grain boundary and the interdendrite. Nanoscale α-Mn dispersoids formed in the grain in the ZTM441 alloy, while no α-Mn formed in the ZTM441-0.3Al alloy instead of nanoscale Al3Mn2 particles. In the ZTM441 as-cast alloy, part of the Zn element is dissolved into the α-Mn phase, and part of the Mn element is dissolved into the MgZn2 phase, but in the ZTM441-0.3Al alloy, there are no such characteristics of mutual solubility. Zn and Mn elements are easy to combine in ZTM441 as-cast alloy, while Al and Mn are easy to combine in ZTM441-0.3Al as-cast alloy. The Mg-Zn phases have not only MgZn2-type crystal structure but also Mg4Zn7- and Mg149Zn-type crystal structure in the ZTM441-0.3Al as-cast alloy. The addition of Al changes the combination of Mn and Zn, promotes the formation of Al3Mn2, and the growth of the grain.

Effect of solid solution temperature on microstructure and mechanical properties of Sc-containing 7085 alloy

The microstructure, mechanical properties, and electrical conductivity of 7085 alloy sheet without and with Sc (0.25 wt%) at different solid solution temperatures were investigated by using OM, SEM, TEM, EBSD, XRD, and the strengthening mechanism of the alloys were analyzed. The results show that the micrometer-scale second phases in the 7085 alloy are mainly the T(AlZnMgCu) phase and the Al7Cu2Fe phase, while Al3(Sc, Zr) particle and the AlZnMgCuSc phase are also formed in the 7085-Sc alloy. The Mg, Zn, and Cu elements in the soluble second phase of both alloys are mainly dissolved as the solid solution temperature increases from 460 °C to 510 °C. The 7085-Sc alloy shows a smaller grain size, higher ultimate tensile strength (UTS, 624 MPa) and yield strength (YS, 580 MPa) after treatment of 480 °C/1 h + 120 °C/24 h. The high strength of 7085-Sc alloy could be attributed to fine-grained strengthening & dislocation strengthening of Al3(Sc, Zr) particles and the precipitation strengthening of MgZn2 phases. The optimum solid solution temperature of 7085 alloy should be controlled in the range of 470–480 °C and that of 7085-Sc alloy is higher, should be 480–490 °C.

Strengthening phase and mechanical property analysis of artificially aged Al7075 – Ni coated Al2024 composites

This technical paper demonstrates the possibilities of nickel (Ni) coated Al2024 powder reinforcement in an Al7075 matrix using the liquid stir casting technique. Additionally, the paper focuses on achieving stable properties by implementing artificial aging heat treatment. To apply the Ni coating, the electroless nickel plating technique was utilized, and a minimum coating thickness of 8 μm was determined to effectively prevent the dissolution of Al2024 powder reinforcements within the Al7075 matrix. Stir casting facilitated the uniform dispersion of the coated Al2024 powder up to a weight percentage of 7%. Subsequently, the Al7075 alloy and composites underwent artificial aging through solution heat treatment (SHT) at 450 °C for 4 h, followed by water quenching and aging at temperatures of 120, 150, and 180 °C. Aging at 120 °C was found to yield superior results compared to aging at 150 and 180 °C, thus identified as the optimum aging temperature. When the Ni coating thickness was increased beyond the optimal 8 μm, the resulting enhancements in hardness for both as-cast and peak-aged specimens, as well as the tensile strength, were not significant. The improvements observed were only marginal, ranging between 2 to 3%. Fracture surface analysis revealed that the predominant fracture mode in the Al7075 alloy was ductile, characterized by dimple rupture. In the as-cast Al7075-(7%, 8 μm) Al2024 composite, a mixed fracture mode comprising both brittle and ductile characteristics was observed. In the peak-aged (120 °C) Al7075-(7%, 8 μm)Al2024 composite, the overall fracture mode exhibited a dominant brittle nature. Analytical techniques including XRD, TEM, and EDS confirmed the presence of Mg2Si, MgZn2, CuAl2, and CuAl2Mg phases in the peak-aged (120 °C) Al7075-(7%, 8 μm) Al2024 composite. These phases contributed to the enhancement of the properties of both the Al7075 alloy and its composites. The developed composites can be used in automobile parts and aerospace applications.

Improving Mechanical Properties, Corrosion Resistance and Biocompatibility of Zn-1Mg-0.3Y Alloys Through Equal Channel Angular Pressing

This paper discusses refining the microstructure of Zn–Mg–Y alloy via equal channel angular pressing (ECAP), leading to enhanced mechanical properties of the Zn alloy. Following ECAP, the strength and elongation of the Zn–Mg–Y alloy increased from 227 MPa and 3% in the as-cast state to 350 MPa and 23%. The increase in strength is primarily attributed to the reduction in grain size, the refinement of the lamellar eutectic Mg2Zn11 phase, and the granular YZn12 phase. Additionally, the nanoscale precipitates generated during ECAP-induced deformation can also contribute positively to strengthening. Beyond strength enhancement, the refinement of the second phase can mitigate stress concentration at the Zn/Mg2Zn11 and Zn/YZn12 interfaces, thereby enhancing the deformability of the Zn alloy. Electrochemical and immersion experiments demonstrate an enhanced corrosion resistance of the Zn–Mg–Y alloy after ECAP processing. This improvement can be primarily attributed to the increased uniformity of the microstructure after refinement, which inhibits the occurrence of localized corrosion. Regarding biocompatibility, Zn–Mg–Y alloys in both the cast and ECAP states exhibited cell viabilities exceeding 100% in MC3T3 cell cultures using 50% and 25% extracts, outperforming the control group of Ti. In summary, the Zn–Mg–Y alloy prepared through ECAP significantly enhances mechanical properties, corrosion resistance, and biocompatibility. These findings open new avenues for advancing the development of improved degradable Zn alloys.

Development of Zn-2Cu-xMn/Mg Alloys for Orthopedic Applications: Mechanical Performance to In Vitro Degradation under Different Physiological Environments.

Zinc (Zn) and its alloys are considered futuristic biodegradable materials for their acceptable mechanical properties, suitable corrosion rate, and good biocompatibility. In this study, we report newly developed biodegradable Zn-2Cu-xMn/Mg (x = 0, 0.1, and 0.5) alloys, aiming to achieve good mechanical strength with excellent elongation, desirable wear resistance, and suitable corrosion rate. The effect of Mn/Mg addition on the structural, mechanical, wear, and degradation behaviors of the Zn-2Cu-xMn/Mg alloys was thoroughly investigated. Degradation and tribological behaviors of the alloys were explored in the presence of simulated body fluid (SBF), Dulbecco's modified Eagle medium (DMEM), and DMEM with a 10% fetal bovine serum (FBS) solution. Alloy elements and hot rolling improve their mechanical properties significantly due to precipitation hardening, grain refinement, and solid solution strengthening owing to the formation of MnZn13 and Mg2Zn11 phases. Among all the alloys, the Zn-2Cu-0.5Mn alloy achieved the highest ultimate tensile strength (UTS) of ∼405 MPa and yield strength (YS) of ∼293 MPa with an excellent elongation of ∼51%. The corrosion behavior of the alloys as determined by a potentiodynamic polarization study under different solutions follows the sequence Zn-2Cu < Zn-2Cu-0.5Mn < Zn-2Cu-0.1Mn < Zn-2Cu-0.1Mg < Zn-2Cu-0.5Mg. The corrosion rate by immersion testing for 30 and 90 days also follows the same sequence. The corrosion rate in different solutions follows the order SBF > DMEM + 10%FBS > DMEM. The addition of Mn/Mg also improves the wear resistance and slows the wear rate under wet conditions. The bending test results also indicate the highest bending strength of ∼375 MPa for the Zn-2Cu-0.5Mn alloy, among all the alloys. The bending and tensile strengths deteriorate continuously after the immersion for 30 and 90 days in the solution of SBF, DMEM, and DMEM + 10%FBS. Therefore, the Zn-2Cu-xMn/Mg (x = 0.1 and 0.5) alloys can be considered potential biodegradable implant materials.

Microstructure and mechanical properties of friction stir processed Zn-Mg biodegradable alloys

Magnesium, iron and zinc-based alloys are potential metallic biodegradable alloys for bioimplant applications. The issues of hydrogen evolution along magnesium’s surface and the release of bulky corroded products of iron alloys during its usage necessitated to look for an alternate alloy system for biodegradable implant applications. Zn-Mg alloy is one such alternate alloy that is widely explored by several researchers. The typical cast microstructure of Zn-Mg alloy contains pro-eutectic α-Zn and eutectic mixture of α-Zn and Mg2Zn11. The cast alloy exhibits poor ductility as the intermetallic Mg2Zn11 phase exists only in eutectic mixture. Therefore, the cast alloys were subsequently processed through hot rolling, hot extrusion and rarely through severe plastic deformation to enhance the mechanical properties. In the current study, probably for the first time, friction stir processing (FSP) has been used to refine the microstructure of Zn-Mg alloys with an intention to enhance the mechanical properties. Indeed, it was a challenge to friction stir process the Zn alloys through friction stir processing, as they have poor ductility (< 10 %) in as-cast condition. By choosing tool rotational speed that can impart significant heat input to the processed regime, this study demonstrated successful FSP of Zn and Zn-(0.5, 1.0 & 2.0) wt% Mg alloys. The pure-Zn and Zn-Mg alloys are FSPed using constant tool traverse speed of 20 mm/ min and variable rotational speeds of 560, 710 and 900 rpm. Hardness of as-cast Zn was 32 VHN whereas addition of 2 % Mg increased it to 105 VHN. Hardness of zinc increased to 39 VHN after FSP using 560 rpm; at the same time, further increase of rotational speed retained the hardness around 40 VHN. On the other hand, hardness of Zn-Mg alloys significantly improved after FSP. Interestingly, hardness of alloys increased with the rotational speed. Usually, increase of rotational speed increases heat input in to the processed regime thus assists the development of coarse microstructure results in hardness degradation. An opposite trend has been observed in the current study. The reasons for this notable observation are found to be refinement of microstructure and redistribution of Mg2Zn11 phase throughout α-Zn matrix that happened during FSP.

Investigation of Zn alloy coating with submicron phases on magnesium alloy by the novel hot-dip process

A Zn alloy coating with submicron phases was fabricated on magnesium alloys by a novel hot-dip process, exhibiting excellent corrosion resistance. The microstructure and phases of coatings were characterized and their correlation with the corrosion performance was investigated. The results indicated that the coating immersed in Zn-3Mg molten bath for 4 s primarily consisted of submicron dot-like Zn phases with well-ordered distribution, while the coating immersed in Zn-3Mg molten bath for 7 s mainly comprised rod-like compact MgZn2 phases with a scattered distribution of Zn phase. The presence of these fine phases of coatings effectively impeded ion permeation in corrosive environments, leading to a significant enhancement in corrosion resistance. Notably, the exceptional corrosion resistance of the coating immersed for 4 s can be attributed to the submicron Zn phase with a grain size of 0.51 μm, resulting in a 62-fold increase in low-frequency impedance value compared to the AZ31 alloy, and a 22-fold decrease in corrosion rate compared to the AZ31 alloy.

Low-cost high-strength Mg–7Zn-xAl-0.3Mn (x=1, 3, 5) cast magnesium alloys via grain boundary strengthening and precipitation strengthening

Obtaining a highly synergistic strength and elongation in cast magnesium (Mg) alloys at low cost is a chronic problem. A series of low-cost and high strength cast Mg–7Zn-xAl-0.3Mn (x = 1, 3, 5) alloys (labeled as ZAM710, ZAM730, and ZAM750 alloys, respectively) were designed based on the phase diagram simulation and prepared successfully by electric resistance furnace. The present results showed that the as-cast ZAM710 alloy was composed of α-Mg, MgZn, AlMn, and Al8Mn5 phases. The MgZn phase disappeared and the Mg32(Al, Zn)49 phase formed as the Al content increased to more than 3 wt%. In addition, with the increase of Al content, the volume fraction of the second phase increased and the grain was refined. The microstructures and mechanical properties of these alloys were improved after heat treatment. Among them, the transmission electron microscopy analysis showed that there were a large number of nanometer precipitation strengthening phases in the aged ZAM750 alloy. One was a rod-shaped Mg4Zn7 phase and the other was a disk-shaped MgZn2 phase. The comprehensive mechanical properties of the ZAM750 alloy were most outstanding, and the tensile strength, yield strength, and elongation were 309.4 MPa, 202.0 MPa, and 6.1%, respectively. The strengthening mechanism of the ZAM750 alloy mainly included grain boundary strengthening and precipitation strengthening, and the contribution values to the yield strength of the ZAM750 alloy were 95.8 MPa and 75.7 MPa, respectively. This work can provide some guidance and new design ideas for the development of low-cost and high-strength cast Mg alloys.

Effect of extrusion parameters on microstructure and mechanical properties of Mg–6Zn–1Mn–0.2Gd alloy

The microstructure, dynamic recrystallization behavior and texture evolution of an as-extruded Mg–6Zn–1Mn–0.2Gd (ZMG610) alloy at different extrusion conditions (extrusion ratios of 25 and 45, temperatures of 350 and 400°C) were investigated. The as-cast ZMG610 alloy was mainly composed of the α-magnesium (α-Mg) matrix, the Mg7Zn3 phase and Mg3Zn6Gd (I phase). A large number of I-phase particles remained in the matrix after homogenization treatment at 330°C up to 24 h. The as-extruded ZMG610 alloy exhibited a bimodal structure consisting of fine dynamically recrystallized grains with a wide orientation spread and coarse undynamically recrystallized grains with a strong basal texture. All as-extruded samples exhibited a typical basal texture with the basal plane of most grains parallel to the extrusion direction. A lower texture intensity could be obtained by increasing both the extrusion ratio and temperature. Optimal mechanical properties (yield strength of 267 MPa, ultimate tensile strength of 360 MPa and elongation of 14.2%) were obtained through the combination of a low temperature (350°C) and a high extrusion ratio (45). Amelioration of mechanical properties highly depended on the synergistic effect of dynamically recrystallized grains, I-phase particles and texture.

Effect of Zn/Mg ratio on the microstructure and mechanical properties of as-cast Al–Zn–Mg–Cu alloys and the phase transformation during homogenization

The content of Zn and Mg directly influences the microstructure characteristics of Al–Zn–Mg–Cu alloys. In the present study, the solidification phases of three as-cast Al–Zn–Mg–Cu alloys with different Zn/Mg ratio (1.5, 1.8 and 2.1 at.%, successively) were thoroughly investigated, and their evolutions during homogenizations were analyzed with the aid of optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The results showed that serious dendritic segregation existed in the as-cast microstructures. In the as-cast alloys with three different Zn/Mg ratio, the secondary phases are represented by non-equilibrium intermetallic phases (Mg(Zn,Cu,Al)2 and Al2Cu) and precipitate MgZn2 phase. Thereinto, the Mg(Zn,Cu,Al)2 phase possessed a majority, which was determined through computational analysis of solidification processes. With the increase of Zn/Mg ratio, the amount of Mg(Zn,Cu,Al)2 phase continuously decreased, while the content of Al2Cu phase showed only minor variation. As the Zn/Mg ratio increased, the strength and hardness of the as-cast alloy gradually improved. The Zn/Mg ratio has a significant impact on the dissolution and transformation of the secondary phases during homogenization process. As the Zn/Mg ratio increased, the melting point of the as-cast eutectic gradually decreased. Additionally, due to the higher diffusion rate of Zn compared to Mg and Cu elements, the dissolution rate of the secondary phase increased accordingly. At relatively low temperatures (380, 410, and 440 °C), phase transformation from the Mg(Zn,Cu,Al)2 phase to the Al2CuMg phase occurred in all three alloys. However, phase transformation was only present in Low/Mid-Zn/Mg ratio alloys at 470 °C. These differences are attributed to the varying diffusion rates of Zn, Mg, and Cu elements during the homogenization process. The implementation of a two-stage homogenization process effectively addresses the issue of residual Al2CuMg phase in Low/Mid-Zn/Mg ratio alloys.

Biodegradable implant application: Electrodeposition of HA/TiO2/ZrO2 coating onto Zn-composite substrates

Zinc has currently emerged as a promising biodegradable metal due to its good biocompatible property and promising degradation behaviour. Additionally, inadequate mechanical strength and a lower cell viability value fall short of what is needed for biodegradable implants. In this work, we used the stir-casting process to create a biodegradable Zn-1Mg-1Cu-1HA (ZHA) and Zn-1Mg-1Cu-1ZrO2 (ZZR) composite onto which ceramics composite coating is done by electrodeposition technique to enhance the biocompatibility. The as-cast sample has uniformly distributed fine MgZn2 and CuZn2 phases in a α-Zn matrix, according to microstructural analysis. The mechanical test confirms that ZZR composite exhibited high tensile and compressive properties, including compressive yield strength of 369.562 MPa, a yield tensile strength of 88.725 MPa and ultimate tensile strength of 116.21 MPa. The result of potentiodynamic polarization test shows that the coated ZZR composite sample gives a corrosion rate value of 0.112 mm/year. From immersion tests, the degradation rate obtained a much lower value after immersing the sample in PBS solution for 55 days (0.067 mm/year). Moreover, an extract of coated ZZR composite shows good cell viability in comparison to the uncoated sample at a concentration of 25%, 50% and 75%. Also, the hemolysis percentage for coated ZZR sample is lower than the other prepared uncoated sample (3.072%) Overall, the result obtained proves that the coated ZZR composite sample can be expected as a capable material for implant application.

Peak hardness stability analysis of Al7075 alloy dispersed with Ni coated duralumin powder during natural aging phenomena

This technical paper presents the successful reinforcement of nickel (Ni) coated duralumin powder in an Al7075 matrix using the liquid stir casting technique and property stability obtained by heat treatment. Ni coating is performed by electroless nickel plating technique where 8 μm coating thickness was observed to be the minimum required to prevent dissolution of the reinforcements (duralumin powder) in the matrix (Al7075). During stir casting it was observed to uniformly disperse the coated duralumin powder up to 7 wt.%. Al7075 alloy and composites were artificially aged with solution heat treatment (SHT) performed at 450 °C for 4 h, water quenched and then aged at 120, 150 and 180 °C. Al7075 alloy and composites were naturally aged for 24 weeks in atmospheric temperature after peak aging. Composites aged at 120 °C exhibited superior results and considered as optimum aging temperature compared to those aged at 150 and 180 °C. Peak hardness values in 7075-7Dp+8T composite improved by 108% and 7075-7Dp+10T composite improved by 110% when compared to peak aged (at 120 °C) Al7075 alloy. Moreover, composites with coated reinforcement displayed a higher resistance to natural aging, with reductions of 53.5 and 54.4% in natural aging tendency compared to the naturally aged Al7075 alloy for 7075-7Dp+8T and 7075-7Dp+10T composites respectively. However, an increase in Ni coating thickness beyond the optimal 8 μm did not significantly improve as cast and peak hardness or natural aging resistance. XRD analysis confirmed that there is presence of CuAl2, CuAl2Mg, Mg2Si, and MgZn2 phases in peak-aged (120 °C) 7075-7Dp+8T sample. Considering the limited impact on property enhancement and the financial burden associated with thicker coatings, a coating thickness of 8 μm is recommended as compared to 10 μm.