Horizontally Solidified Al–3 wt%Cu–(0.5 wt%Mg) Alloys: Tailoring Thermal Parameters,Microstructure, Microhardness,and Corrosion Behavior

In the present experimental investigation, Al–3 wt%Cu and Al–3 wt%Cu–0.5 wt%Mg alloys castings are produced by a horizontal solidification technique with a view to examining the interrelationship among growth rate(G_R), cooling rate(C_R), secondary dendrite arm spacing(λ_2), Vickers microhardness(HV), and corrosion behavior in a 0.5 M NaCl solution.The intermetallic phases of the as-solidified microstructures, that is, h-Al_2Cu, S–Al_2CuMg, and x-Al_7Cu_2 Fe, are subjected to a comprehensive characterization by using calculations provided by computational thermodynamics software, optical microscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Moreover, electrochemical impedance spectroscopy and potentiodynamic polarization tests have been applied to analyze the corrosion performance of samples of both alloys castings. Hall–Petch-type equations are proposed to represent the HV dependence on λ_2. It is shown that the addition of Mg to the Al–Cu alloy has led to a considerable increase in HV; however, the Al–Cu binary alloy is shown to have lower corrosion current density(i_(corr)) as well as higher polarization resistance as compared to the corresponding results of the Al–Cu–Mg ternary alloy.     

Effect of Microstructure on Corrosion Behavior of Mg–Sr Alloy in Hank's Solution

Mg–Sr alloy has been studied as a potential biodegradable material with excellent bioactivity to promote the bone formation. However, its degradation behavior needs to be well controlled to avoid the negative effect, which is important for future application. Therefore in this study, the microstructure and its effect on corrosion behavior of an Mg–1.5 Sr alloy were investigated. The microstructures of the alloy under different processing procedures were characterized by both optical and scanning electron microscopes. The corrosion performance was studied in Hank's solution using immersion,potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests. The results showed that the grain size and the amount and distribution of b-Mg_(17)Sr_2 had obvious effects on the corrosion behavior of Mg–Sr alloy. The smaller the grain size was, the more the protective surface layer formed on Mg–Sr alloy, and the higher the corrosion resistance was. For the as-cast Mg–Sr alloy, the network-like second phases precipitated along the grain boundaries could not hinder the corrosion due to their own corrosion cracking accelerating the intergranular corrosion. However, the refinement of second phases increased the corrosion resistance of the as-extruded alloy. After solution treatment at 450 °C for 5 h, the grains in the alloy did not grow much and b-Mg_(17)Sr_2 phases homogenously distributed in the alloy, resulting in the increase in corrosion resistance. However, after aging treatment, large amount of precipitated second phases increased the galvanic corrosion of the alloy, accelerating the development of corrosion.     

Joint Characteristics and Corrosion Properties of Bypass-Current Double-Sided Arc-Welded Aluminum 6061 Alloy with Al–Si Filler Metal

Sheets of aluminum 6061 alloy were welded using bypass-current double-sided arc welding with Al–Si filler wire to investigate the effect of Al–Si intermetallic compounds on the microstructure, microhardness and corrosion behavior of weld joint. Experimental results indicated that the Al_(4.5)FeSi phase in the topside of the weld joint was finer than that in the backside and newly formed phase of Al_(0.5)Fe_3Si_(0.5)was observed in the backside. The formation of reinforcing phases of Al–Fe–Si in the weld improved the microhardness of the weld by about 18%. The corrosion resistance of the weld zone was greater than that of the base metal, while the corrosion current displayed opposite, and the corrosion resistance of the weld region was better than that of the base metal.     

Manipulating Precipitation Through Thermomechanical Treatment to Control Corrosion Behavior of an Al–Cu–Mg Alloy

Controlling the precipitation through thermomechanical treatment is an important method to improve the corrosion resistance of Al–Cu–Mg alloys. In this study, the corrosion behaviors of Al–Cu–Mg alloys in the solution-treated state and retrogressiontreated state under cold rolling deformation and then natural aging were investigated. In the solution-treated series alloys, the cold-rolled deformation improved the resistance to intergranular corrosion by suppressing the precipitation of the S-phas...     

Dendritic Boundary Corrosion of AA2198 Weld Using Fiber Laser Welding with Al–Cu Filler Wire

The microstructures and corrosion behaviors of AA2198–T851 alloy and weld were analyzed under corrosive conditions.Weld was formed using an innovative fiber laser welding process with AA2319 Al–Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaCl solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical components and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al–Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heataffected zone with a compact protective film.     

Corrosion of New Zirconium Claddings in 500 ℃/10.3 MPa Steam: Effects of Alloying and Metallography

With the aim of improving corrosion resistance of rod cladding for in-service and accident conditions, six new zirconium alloys(named N1–N6) have been designed.The contents of Sn and Nb were optimized for better behavior at high-temperature pressurized water, and Fe, Cr, V, Cu or Mo elements were added to the alloys to adjust the corrosion behavior.The current work focused on the rapid corrosion behavior in 500 ℃/10.3 MPa steam for up to 1960 h, aiming to test the corrosion resistance at high temperature.The structure of matrix and properties of second-phase particles(SPPs) were characterized to find the main differences among these alloys.All the six alloys exhibited better corrosion resistance than N36, and N1 was shown to have the best performance.A careful analysis of the corrosion kinetics curves revealed that Cr was beneficial for severe condition.Elements Fe, Cr, V, Cu or Mo aggregated into SPPs with different concentrations and structures.This was demonstrated to be the main reason for different corrosion resistance.Due to good processing control, all alloys had a uniform structure and a uniform distribution of SPPs.As for N4, N6 and N36, the existing of large-size SPPs(450 nm) might be a contributing factor of the relatively poor corrosion resistance.     

Corrosion Behaviors of Pure Titanium and Its Weldment in Simulated Desulfurized Flue Gas Condensates in Thermal Power Plant Chimney

The corrosion behaviors of pure titanium and its weldment welded by tungsten inert gas(TIG) welding in simulated desulfurized flue gas condensates in thermal power plant chimney were investigated using potentiodynamic polarization,electrochemical impedance spectroscopy(EIS) and immersion tests.The effects of heat input and shielding gases on the corrosion behavior of the welded titanium were also studied.Grain coarsening and Widmansta¨tten structure were found in both the fusion zone and the heat-affected zone.The welded titanium exhibited active–passive behavior in the simulated condensates.Both the polarization curves and EIS measurements confirmed that TIG welding process with different parameters had few effects on the corrosion behavior.It was proved that the microstructure changes were not the key material factors affecting the corrosion behavior of pure titanium under the test conditions,while the oxide film had remarkable effect on improving the corrosion resistance.     

Influence of Alloying Element Addition on Cu–Al–Ni High-Temperature Shape Memory Alloy without Second Phase Formation

In this study,the effects of rare earth Gd and Fe elements on the microstructure,the mechanical properties and the shape memory effect of Cu–11.9Al–3.8Ni high-temperature shape memory alloy were investigated by optical microscopy,scanning electron microscopy,X-ray diffraction and compression test.The microstructure observation results showed that both Cu–11.9Al–3.8Ni–0.2Gd and Cu–11.9Al–3.8Ni–2.0Fe–0.2Gd alloys displayed the fine grain and singlephase b01martensite,and their grain size was about several hundred microns,one order of the magnitude smaller than that of Cu–11.9Al–3.8Ni alloy.The compression test results proved that the mechanical properties of Cu–11.9Al–3.8Ni alloy were dramatically improved by alloying element additions due to grain refinement and solid solution strengthening,and the compressive fracture strains of Cu–11.9Al–3.8Ni–0.2Gd and Cu–11.9Al–3.8Ni–2.0Fe–0.2Gd were 12.0%and 17.8%,respectively.When the pre-strain was 10%,the reversible strains of 5.4%and 5.9%were obtained for Cu–11.9Al–3.8Ni–0.2Gd and Cu–11.9Al–3.8Ni–2.0Fe–0.2Gd alloys after being heated to 500°C for 1 min,and the obvious two-way shape memory effect was also observed.     

Tribological Properties of Nanostructured Al/Al_(12)(Fe,V)_3Si Alloys

Tribological behavior of nanostructured pure Al and Al–Al12(Fe,V)3Si alloys containing 27(FVS0812) and 37(FVS1212) vol% of Al12(Fe,V)3Si precipitates was investigated. All samples were prepared using mechanical alloying followed by hot pressing. Wear tests were performed at room temperature using a pin-on-disk machine. Results showed that the presence of Al12(Fe,V)3Si precipitates increases the wear resistance of nanostructured Al, and the wear resistance increases with increasing the Al12(Fe,V)3Si content. Scanning electron microscopy images of worn surfaces and wear debris demonstrated that abrasion and adhesion are the governing wear mechanisms for the nanostructured FVS0812 alloy at 2 and 5 N normal loads, whereas for the nanostructured FVS1212 alloy, the dominant wear mechanism is abrasion at these loads. A mechanically mixed layer(MML) containing Fe and O was formed on the worn surfaces of FVS0812 and FVS1212 samples at 10 N normal load. Formation and delamination of MML controls the wear behavior of these samples at the normal load of 10 N. It is also found that the presence of Al12(Fe,V)3Si precipitates decreases the friction coefficient of nanostructured Al.     

Microstructure and Wear Behavior of Cermet/Iron Alloy Cladding Layers on A6061 Alloy Coated by Resistance Seam Welding Method

Cermet/iron alloy cladding layers were coated on the surface of Al–Mg–Si alloy(A6061) plates by resistance seam welding method with tungsten carbide(WC) and high-carbon iron alloy(SHA) powders.The cladding layer consisted of WC reinforcement,SHA binder,A6061 and Fe Al3.The effect of WC ratio(30 wt%,50 wt% and 70 wt%) on the microstructure and wear behavior of the cladding layers was investigated in detail.Abrasive wear test was performed under two kinds of load condition by using a rubber wheel apparatus to evaluate wear resistance.The results showed that the wear resistance of the cladding layer was improved by 3.5–5 times than that of the substrate.At lower load,the wear resistances of the samples 30% and 70% WC were nearly the same,which suggested that Fe Al3 played an important role in improvement of the wear resistance instead of WC.While at higher load,the amount of WC determined the wear resistance of the cladding layer.Furthermore,wear behavior of these cladding layers was explained with reference to the observed microstructure of the worn surface.     

Cerium-Based Sealing Treatment of Mg–Al Hydrotalcite Film on AZ91D Magnesium Alloy

An environment-friendly cerium-based sealing treatment was developed to improve the surface integrity and corrosion resistance of Mg–Al hydrotalcite film on AZ91D magnesium alloy. The cerium dioxide was generated through three stages namely nucleation, growth and dissolution, modifying the surface of AZ91D Mg alloy, and the hydrotalcite film became integral after being treated for 30 min. The results of polarization curves showed that the anti-corrosive performance of the hydrotalcite film was enhanced by the sealing treatment. Moreover, the immersion tests and electrochemical impedance spectrum measurements also demonstrated that the sealed hydrotalcite film provided a longer-term protection of magnesium alloy from corrosion as compared to the unsealed one.     

Corrosion Behavior of Fe–Al Coatings Fabricated by Pack Aluminizing Method

In this study,the two kinds of Fe–Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures.The corrosion behavior of the Fe–Al coatings in artificial seawater was investigated by the electrochemical and weight loss techniques.Results show that the thickness of coating layer increases with increasing aluminizing temperature.The coatings exhibit high micro-hardness and good metallurgical bonding with the substrate.In comparison with the steel substrate,the corrosion current density Icorrof the Fe–Al coatings is always lower than that of substrate,about 1/38 or 1/33 after 2 h immersion,and 1/3 or 1/6 for 720 h immersion.As can be seen from the weight loss curve,the Fe–Al coatings show less loss than that of the substrate within 30-day immersion.The corrosion products formed on the surface of the coatings include oxides of Al,Mg,Fe and Ca,and pitting defect has also been found.The Fe–Al coating with higher content of Fe_2Al_5 has better corrosion resistance.     

Laser cladding of Al＋Ir powders on ZM5 magnesium base alloy

Laser cladding of preplaced Al ＋ Ir powders on a ZM5 magnesium alloy was performed to enhance the corrosion resistance of the ZM5 magnesium alloy. A metallurgical bond was obtained at the coating/substrate interface. The corrosion potential （Ecorr） of the laser cladded sample was 169 mV positive to that of the untreated ZM5 substrate,while the corrosion current （Icorr） was some one order of magnitude lower. The laser cladded sample,unlike the untreated ZM5 substrate,showed a passive region in the polarization plot. Immersion tests confirmed that the corrosion resistance of the laser cladded ZM5 sample was significantly enhanced in 3.5 wt.% NaCl solution. The Al-rich phases of AlIr,Mg17Al12,and Al formed in the cladding layer and the rapid solid characteristics were contributed to the improved corrosion behavior of the coating.     

Effect of Phase Transformation During Long-Term Solution Treatment on Microstructure,Mechanical Properties,and Bio-corrosion Behavior of Mg–5Zn–1.5Y Cast Alloy

The influence of long-term solution treatment for various intervals on the microstructure,mechanical properties,and corrosion resistance of the as-cast Mg–5Zn–1.5Y alloy was investigated.Variation of secondary phases was studied during solution treatment through thermal analysis test and thermodynamic calculations.Tensile and hardness tests,as well as polarization and immersion tests,were performed to evaluate the mechanical properties and corrosion behavior of the ascast and heat-treated alloy,respectively.Results show that solution treatment transforms I-phaseinto W-phaseas well as dissolves it into the a-Mg matrix to some extent;therefore,the amount of W-phase increases.Moreover,prolonged solution treatment decreases the volume fraction of the phases.In the first stage of solution treatment for 14 h,the tensile properties significantly increase due to the incomplete phase transformation.Although long-term solution treatment sharply decreases the tensile and hardness properties of the alloy,it improves the corrosion resistance due to the transformation of I-phase into W-phase.In fact,it decreases corrosion potential and simultaneously dissolves intermetallic compounds into the a-Mg matrix,resulting in the reduction in galvanic microcells between the matrix and compounds.It is found that the optimum time for long-term solution treatment is 14 h,which improves both corrosion behavior and mechanical properties.     

Study on Phosphating by Ultrasonic Wave at Room Temperature for Sintered NdFeB Magnet

The corrosion behavior of a NdFeB magnet obtained at room temperature,with and without ultrasonic were investigated.The corrosion resistance was investigated by corrosion immersion tests in 3 wt%neutral NaCl solutions,potentiodynamic polarization tests and electrochemical impedance spectroscopy(EIS).The morphology of the conversion coatings on NdFeB surface were analyzed by scanning electron microscopy(SEM).And the forming mechanism of coatings was studied by potential-time curves.The tests of corrosion resistances show that the combination of phosphating treatment with ultrasonic will further improve the corrosion resistance of the NdFeB.The SEM also confirms that phosphating coating under ultrasonic is more homogeneous and compact.     

Cu/Li Ratio on the Microstructure Evolution and Corrosion Behaviors of Al–xCu–yLi–Mg Alloys

The microstructure evolution and the corrosion feature of Al–x Cu– y Li–Mg alloys( x : y = 0.44, 1.65 and 4.2) were systematically investigated under the same artificial aging conditions. The relationships between types of precipitates and mechanical performance, as well as electrochemical behaviors, were discussed. Our results show that different types of precipitates can be obtained in alloys with different Cu/Li mass ratios, which significantly influences the mechanical performance of the alloys and substantial corrosion behaviors. Specifically, the analogous corrosion evolution in the aging Al– x Cu– y Li–Mg alloys was first ascertained to be derived from the growth mechanism of the precipitates at the grain boundary(GB). Moreover, a small number of GB precipitates can be obtained in the aged alloy with the lowest Cu/Li mass ratio, thereby resulting in the largest intergranular corrosion resistance. A higher proportion of the GB T_1 phase in the continuous precipitates induces higher corrosion sensitivity in alloy with a high Cu/Li mass ratio.     

Effect of Shot Peening and Plasma Electrolytic Oxidation on the Intergranular Corrosion Behavior of 7A85 Aluminum Alloy

The effects of shot peening(SP) and plasma electrolytic oxidation(PEO) on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85(AA 7A85) were investigated by electrochemical polarization and electrochemical impedance tests.The intergranular corrosion mechanism of SP,PEO and PEO combined with sealingtreated AA 7A85 was studied by the metallographic analysis,residual stress testing,X-ray diffractometer analysis and scanning electron microscopy.The results show that AA 7A85-T7452 is very sensitive to intergranular corrosion.SP would significantly improve its intergranular corrosion resistance.This is attributed to the combination action of residual compressive stress and grain refinement.PEO would reduce the largest corrosion depth by 41.6%.Moreover,PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide coating.However,PEO combined with the SiO2sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.     

Enhanced Mechanical Properties,Corrosion Behavior and Bioactivity of Ti-based Bulk Metallic Glasses with Minor Addition Elements

In this research, corrosion behavior, mechanical properties and bioactivity of Ti–Zr–Cu–Pd–Sn bulk metallic glasses with minor addition of Au, Pt, Nb or Ta elements were investigated. The results revealed that minor additions of the elements were beneficial to enhancing mechanical properties and corrosion resistance of Ti-based bulk metallic glasses.Minor addition of the element(especially with Nb and Ta addition) results in the improvement in plastic deformation ability due to the existing of nanoparticles with a size smaller than 10 nm in glassy matrix, inhibiting the deformation of the shear bonds. Enrichments of Ti and Zr elements in oxide layer were responsible for high corrosion resistance. The bioactivity of Ti-based bulk metallic glasses was also investigated. The best combination of large plastic deformation ability, good corrosion resistance and bioactivity in Ti_(40)Zr_(10)Cu_(33)Pd_(14)Sn_2Ta_1 BMG was obtained.     

Influence of Voltage on the Corrosion and Wear Resistance of MicroArc Oxidation Coating on Mg-8Li-2Ca Alloy

Calcium phosphate(CaP) coatings were prepared on Mg–8Li–2Ca magnesium alloy by micro-arc oxidation(MAO) in an alkaline Na_3PO_4–Ca[C_3H_7O_6P] base solution at the different applied voltages. Scanning electron microscope and X-ray diffraction were employed to characterize the microstructure and phase composition of the coatings, respectively. The corrosion resistance of the coatings was assessed by potential dynamic polarization curves, electrochemical impedance spectroscopy and hydrogen evolution experiment in simulated body fluids solution. The friction and wear properties were evaluated by friction and wear testing machine. The results demonstrate that the coating surface is porous and mainly composed of MgO, Ca_5(PO_4)_3(OH) and CaH_2P_2O_5. With the increase in voltage, the corrosion resistance and wear resistance of the MAO coating are both enhanced. The corrosion current density of the MAO coating decreases about two orders of the magnitude compared to the substrate. Additionally, wear and corrosion mechanisms are discussed.     

Corrosion Resistance of Co-containing Maraging Stainless Steel

Corrosion resistance behavior of Co-containing maraging stainless steels was investigated. Neutral salt spray and polarization test showed that maraging stainless steel with high Co content showed poor corrosion behavior. Microstructure observation proved that segregation of Cr in the matrix deteriorated its corrosion resistance. The surface morphology of the aged maraging stainless steel with high Co content indicated that during passivation process, the newly formed passive film with sinusoidal distribution readily destroyed by the corrosive medium, hence, causing poor corrosion resistance. Moreover, through first-principles calculation it was proved that Co increased Fe–Fe ferromagnetic interaction which facilitated the formation Cr-rich clusters.