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Effect of Ce addition on the microstructures, mechanical properties and electrochemical properties of Al-Cu-Mn-Mg-Fe lithium battery alloy was investigated by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile testing and electrochemical testing. Experimental results indicate that Ce addition resulted in the formation of Al8Cu4Ce phase in the Al-Cu-Mn-Mg-Fe alloy. The Ce-containing precipitates nucleated and grew up along the surface of Al6(Mn, Fe) precipitates. Al6(Mn, Fe) precipitates could be remarkably refined by Ce alloying. The aging precipitation behavior of Sˈ phases could be promoted after Ce addition to the alloy. In comparison with Ce-free alloy, the Ce-containing alloy had higher tensile strength at both low temperature and elevated temperature. Especially at 200 °C, the yield strength and tensile strength of Ce-containing alloy substantially increased by 23.4% and 27.08%, respectively. Potentiodynamic polarization testing indicated that the Ce-containing alloy had a more positive corrosion potential and a lower corrosion current density.

Effects of CeLa addition on the localized corrosion and electrochemical corrosion behavior of Al-Cu-Mn-Mg-Fe lithium battery shell alloy were investigated by immersion testing and electrochemical testing in 0.6 M NaCl solution at different temperatures. Experimental results indicated that CeLa addition resulted in the formation of AlCuCe/La (Al 8 Cu 4 Ce and Al 6 Cu 6 La) local cathodes and corrosion activity of the main intermetallic particles decreased in the order of Al 2 CuMg, AlCuCe/La, Al 6 (Mn, Fe). Corrosion potential shifted positively due to CeLa alloying. Corrosion current density of the CeLa-containing alloy was lower than that of the CeLa-free alloy at room temperature. At room temperature, there was no obvious surface passivation for both alloys. At 80 °C CeLa addition resulted in a wide passive region at the anode polarization region. Electrochemical impedance spectroscopy (EIS) analysis also indicated that corrosion resistance of the CeLa-containing alloy was much higher than that of the CeLa-free alloy.

The structural evolution of the oxide films at 25–450 °C on nanocrystalline (NC) and coarse crystalline (CC) 304 stainless steels (SS) was investigated. The structure of the oxide film on both NC and CC SSs was observed to undergo transient processes from a bi-layer to a single-layer and then back to a bi-layer when the temperature changed from the low range (25–150 °C) to the medium range (150–300 °C) and subsequently to the high range (300–450 °C), respectively. These formation mechanisms of the oxide films on SS were attributed to the different diffusion properties of Cr and Fe in the three temperature ranges. The thickness of the oxide films was similar between the NC and CC SSs below 300 °C due to their similar Cr ox /Fe ox concentration ratios in their oxide films at this temperature. Above 300 °C, Cr diffusion enhancement in the NC matrix led to a higher Cr ox /Fe ox ratio and better compactness of the oxide film, which resulted in a slower atomic diffusion rate in the oxide film and a thinner oxide film. Therefore, the temperature of 300 °C was concluded to be the critical temperature of the detectable Cr diffusion enhancement in the NC SS compared to the CC SS.

Development of high strength lithium battery shell alloy is highly desired for new energy automobile industry. The microstructures and mechanical properties of Al-Cu-Mn-Mg-Fe alloy with different CeLa additions were investigated through optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rietveld refinement and tensile testing. Experimental results indicate that Al 8 Cu 4 Ce and Al 6 Cu 6 La phases formed due to CeLa addition. Addition of 0.25 wt.% CeLa could promote the formation of denser precipitation of Al 20 Cu 2 Mn 3 and Al 6 (Mn, Fe) phases, which improved the mechanical properties of the alloy at room temperature. However, up to 0.50 wt.% CeLa addition could promote the formation of coarse Al 8 Cu 4 Ce phase, Al 6 Cu 6 La phase and Al 6 (Mn, Fe) phase, which resulted in weakened mechanical properties.

The 304 austenitic stainless steel (ASS) undergone equal-channel angular pressing (ECAP) was annealed to achieve a strength-ductility balance through bi-modal microstructure (BMS) tailoring. The coarse grained ASS was first refined down to the nano-grained (NG) level by ECAP for eight passes. The NG microstructure with high dislocation density offers higher strength but lower ductility. The recrystallization curve of NG ASS exhibits three distinct regions including the recovery region below 650 °C, the recrystallization region from 650 °C to 800 °C, and the grain growth region above 800 °C. The results of microstructure observation and tensile test show that the annealing NG ASS at 750 °C for 30 min produces the BMS consisting of 62 v/v% ultrafine grains with average size 350 nm and 38 v/v% coarser grains with average size 1.4 µm. Consequently this BMS ASS presents high strength and high ductility with yield strength 725 MPa, tensile strength 930 MPa, uniform elongation 34.5% and total elongation 40.6%. The present study provides an easy route to enhance the mechanical properties of face center cubic metal and alloys, and thus is of wide application potential.

Dense and porous nickel-free Ti–11Nb–4O (at.%) alloys with Af temperature closed to body temperature were fabricated by conventional powder metallurgy (sintering) method from elemental Ti and Nb powders. Their microstructure, phase transformation temperature, superelasticity and mechanical properties at room temperature were investigated by optical microscopy, X-ray diffraction, differential scanning calorimetry and compression testing. It has been found that the phase temperature of Ti–11Nb–4O alloy by sintering is different from that by smelting and cold-rolling method due to the introduction of oxygen during powder mixing and sintering, and the Af temperature can reach up about 40 °C by reducing Nb content and controlling oxygen. Near dense Ti–11Nb–4O alloys can exhibit more than 5.4% superelasticity, high cyclic stability up to 100 cycles, high yield strength of 1.48 GPa and small strain hysteresis of 0.14% at room temperature. Moreover, porous Ti–11Nb–4O alloys with 29.4% porosity also can show complete superelasticity of near 3%, yield strength of 800 MPa and elastic modulus of 24.5 GPa at room temperature, which can be considered as one of perfect bone replacement materials in conjunction with their excellent biocompatibility. Keywords: Ni-free shape memory alloys, Superelasticity, Porous alloys

The structure and compactness of the passive films on nanocrystalline (NC) and coarse crystalline (CC) 304 stainless steels (SSs) are investigated. A bi-layer passive film composed of an inner Cr2O3-rich layer and an outer Fe2O3-rich layer is obtained on both NC and CC 304SSs. The lower oxide formation potential Uox(Cr) of chromium causes the Cr2O3-rich inner layer to form initially, and when the surface potential of the passive film increases due to Cr2O3 formation, Fe2O3 with a higher formation potential Uox(Fe) forms and predominates in the outer layer as a result of the higher diffusion rate of Fe than that of Cr across the inner layer. Compared with the CC-304SS, the inner layer of the passive film on the NC-304SS possesses a higher Cr2O3 content, which is attributed to the greater nucleation sites and faster growth rate of Cr2O3 in NC-304SS and is believed to be responsible for the higher compactness of the passive film on NC-304SS.

The Ti-(11–15)Nb–18Zr (at.%) alloys with low oxygen content and fine grain microstructure were successfully prepared by low temperature sintering after dielectric barrier discharge plasma (DBDP) milling of hydride (TiH2, ZrH2) and Nb powders. Hydride powders effectively reduced the oxygen content and lower the sintering temperature of Ti- (11–15) Nb–18Zr alloys. DBDP milling quickly refined and activated the TH2-Nb-ZrH2 powders without increased contamination by oxygen. The decrease in sintering temperature (as low as 1000 °C) helped to reduce the grain size of the Ti-(11–15)Nb–18Zr alloys to 3–8 μm, which has significantly increased the strength of the alloys. The reduction of oxygen content (as low as 0.4 wt%) in the Ti-(11–15)Nb–18Zr alloys benefited the superelasticity of the alloys. Among them, the Ti–12Nb–18Zr alloys presents an excellent superelasticity of about 1.5%, which is the highest value ever reported in the sintered Ti–Nb based SMAs.

In this work, an attempt was made to further promote the wear and friction behavior of dual-scale structured Al–12 wt% Sn bearing alloys by coupling with a nano-Si@Sn composite. A so-called tri-modal Al–Sn–Si (denoted as CG-30 Si-containing alloy), which exhibited increased bulk hardness and improved distribution and refinement of the Sn phase, was produced by combining mechanical alloying and conventional powder sintering. The wear performance of the Si-containing and Si-free alloys was differentiated by performing both block-on-ring and ball-on-disk testing. Moreover, the addition of nano-Si@Sn composites to the dual-scale Al–Sn matrix resulted in significant reductions of the friction coefficient and wear volume. These improvements in wear behavior stemmed from the polishing effect of fine Si particles on the counterface, and Sn-rich clusters that acted as lubricants on the worn surface; together, the polishing effect and lubrication led to the formation of a smooth tribolayer, and hence, a decrease in the tendency for abrasive wear. Abrasive wear was also reduced by an increase in the alloy hardness with the addition of Si. As such, Sn-phase modification via Si addition constitutes a promising method for preparing self-lubricating Al-based alloys.

The mechanism of microstructure evolution of 304 stainless steel (SS) during equal-channel angular pressing (ECAP) at 500 °C was investigated systematically by optical microscope (OM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results show that the refining mechanism of microstructure of 304 SS during ECAP behaviors as a hybrid model consisting of dislocation-subdivision mechanism and twin fragmentation mechanism, resulting in three kinds of nanostructure domains: (1) the equiaxial nano-grains with curving grain boundaries (GBs) having high angles of misorientation resulted from the cross-slip and movement of dislocations; (2) the equiaxial nano-grains with smooth and distinct boundaries resulted from the intersection between primary deforming twin bundles; (3) the secondary nano-twins formed in the primary deforming twins. The average nano-grain size ultimately obtained is in the range of 80 nm to 120 nm and the nano-twins have a width of 20–40 nm and a length of 100 to a few hundred nm. A low content about 10% (V/V) of deformation-induced martensite (DIM) is obtained in the first pass and remains almost constant during further passes of ECAP. The refining mechanism of DIM is also a hybrid model, including the refinement of banded DIM by the intersection with slipping bands and the newly induced fine martensite in submicron and nanometer grained austenite matrix.

Effects of Zr addition on the microstructure, mechanical and electrochemical properties of Al–Mn–Si–Zn alloy were investigated. Transmission electron microscopy (TEM) observations reveal that, in as-annealled state, the precipitates in the Zr-containing alloy are finer and more dispersive than those in the Zr-free alloy. Whereas, in simulated brazing state, a weaker precipitation is found in the Zr-containing alloy. Tensile testing results indicate that, with Zr additon, comprehensive mechanical properties of the as-annealed alloys could be significantly improved but weakened for the simulated brazing alloy. Electrochemical testing results reveal that, with Zr addition, the corrosion resistance of the as-annealed alloy decreases. However, after the simulated brazing treatment, such a negative effect of Zr element on the corrosion behavior of the alloy could be negligible.

Due to severe application environment lithium battery shell of new-energy automotives requires increasing demands for using high performance aluminum alloys. In the present work, effect of Ce addition on the microstructure, tensile and electrochemical properties of an Al–Cu–Mn–Mg–Fe alloy were investigated through using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), tensile tests and electrochemical tests. The experimental results indicated that the addition of Ce element could promote the precipitation of second phases. With addition of 0.36% Ce, high melting point Al8Cu4Ce phase and many Al20Cu2Mn3 particles could be found. In addition, the precipitation of conventionally dominant phase of Al2Cu could be suppressed in alloy. The Ce addition was found to result in enhanced tensile strength and improved corrosion resistance.

Nickel-free Ti–22Nb–6Zr alloys were fabricated by conventional powder metallurgy sintering method. X-ray diffractometer (XRD) investigation showed that the as-sintered alloys mainly consisted of β phase, with a few needle-like α phase precipitates. Differential scanning calorimetry (DSC) measurement in the temperature ranging from −70 °C to 400 °C and constant stress thermal cycling test by dynamic mechanical analysis (DMA) were unable to reveal the martensitic start temperature of sintered Ti–22Nb–6Zr alloys. Therefore low temperature compression tests were carried out to evaluate their phase transformation behavior indirectly. There was an obvious drop of both Young’s modulus and recoverable strain at −85 °C ∼ −80 °C in the Young’s modulus-temperature and recoverable strain–temperature curves of sintered Ti–22Nb–6Zr alloys respectively, which was attributed to the occurrence of thermal elastic martensitic transformation at this temperature. At the testing temperature of −85 °C, a superelasticity of as high as 5.9% was achieved in the sintered alloys. The results had revealed that sintered Ti–22Nb–6Zr alloys own a great superelasticity intrinsically and would exhibit a much greater superelasticity at room temperature if their martensitic transformation start temperature ( M s ) were closer to room temperature. Along with their noble biocompatibility, sintered nickel free Ti–22Nb–6Zr alloys are thus thought to be potentially competitive biomaterials for biomedical applications.

The dual-scale structured Al–Sn based alloys are potential alternative for journal bearings of automotive application due to their excellent tribological and mechanical properties. In this work, the authors attempted to further promote wear properties of dual-scale structured Al–12 wt% Sn alloys by Mg addition. It has been found that appropriate Mg addition could increase wet-ability and reduce divorced Sn eutectics, resulting improved distribution of Sn phase, strength and ductility. Moreover, the mechanism for the improvement of the wear properties of Mg-containing Al–Sn alloy was revealed, and could be summarized as follows: (1) The improved transportation and distribution of the Sn nanophases, including nanoparticles and nanowires, towards the worn surface effectively reduced the friction coefficient; (2) enhanced Mg-oxide film and tribolayer formation on the mating surfaces and (3) increased stability of tribolayer owing to better combination of the strength and ductility. But excessive Mg addition led to too high amount of Mg2Sn and Mg17Al12 intermetallic phases, which worsen the wear properties. The dual-scale CG-30 Al–Sn with 1.2 wt% Mg addition exhibits the best wear performance under the present experiment conditions.

A mechanism for significant improvement of wear properties has been investigated. This operates by inducing a dual-scale structure consisting of coarse-grains (CG) and ultrafine-grains (UFG) in Al–12 wt%Sn alloys, in comparison with uniform UFG or CG structured alloys. It has been found that a dynamic steady tribolayer consisting of fine crystalline oxides plays a dominant role in improving the wear properties of both the UFG and dual-scale alloys. For the CG alloys, poor wear properties, caused by delamination wear of the tribolayer, could not be maintained on the worn surface. The tribolayer is formed on the worn surface by compacting and tribo-sintering of fine loose particles produced by sliding wear. However, the damage of the dynamic steady tribolayer is governed by the matching between ductility and strength of the matrix. The low ductility of the UFG alloy substrate causes the tribolayer to suffer crack damage rather easily, which limits any further improvement of its wear resistance. In contrast, for the CG alloys, the tribolayer is broken up and extruded into the matrix as a result of its low strength and a stable tribolayer could not be formed. The dual-scale structured alloy has excellent ductility–strength matching, and therefore a dynamic stable tribolayer can easily be maintained on the worn surface, leading to excellent wear performance.

We present in this work evidence that significant improvement of wear behavior can be achieved by creating a dual-scale structure. An Al–12 wt%Sn bearing alloy consisting of mixtures of nanocrystalline (NC) Al–Sn powder and coarse-grained (CG) Al–Sn powder was produced by a combination of mechanical alloying and conventional powder sintering. The extent of the improvement in wear properties was related to the ratio of NC/UFG to CG, and the best properties were achieved at a ratio of 30 wt% CG. With this ratio, this dual-scale Al–Sn (CG-30) alloy had a wear resistance about 1.5 times greater than that of the monolithic NC/UFC alloy prepared by mechanical alloying, about twice that of the monolithic CG alloy. The friction coefficient decreased by nearly 13% of the CG alloy. The detailed wear mechanism investigation revealed that an optimized combination of hardness and toughness is a key for the improvement of wear properties in the dual-scale material.

Effect of microstructure change on the corrosion behaviour of equal channel angular pressed (ECAPed) 304 stainless steel (SS) was investigated. Nanostructure (80–120 nm) was obtained after 4 and 8 passes ECAP and exhibited a higher corrosion resistance than as-received SS. However, thickness and composition of the passive film formed in air at room temperature on both as-received and 8-pass samples show little difference, indicating that Cr diffusion is not enhanced by the formation of nanostructure. The improved corrosion resistance of ECAPed SS is not caused by thickness or composition change, but by compactness and stability improving of the passive film.

The effect of Zn addition on the microstructure, tensile properties and electrochemical properties of as-annealed 3003 Al alloy was investigated through TEM observations, tensile tests and Tafel polarization analysis. High density precipitates are observed in the Zn-containing alloys and the alloy with 1.8% Zn addition also has rod-like precipitates. Tensile test results indicate that Zn has a great effect on tensile strength of 3003 Al alloy. The alloy with 1.5% Zn addition has the highest ultimate tensile strength. The electrochemical results indicate that Zn addition to 3003 Al alloy also has great impact on the corrosion potential of the 3003 Al alloy in 0.5% NaCl solution and ethylene glycol-water solution. The corrosion potential varies with the Zn content and shifts negatively.

Electroless Ni–P and Ni–Co–P deposits were obtained on Al substrate. Their surface morphology, microstructure and composition were analyzed using SEM and XRD. Their corrosion resistance was characterized by anodic polarization curves. Based on the measurement of the thickness, electrical conductivity and magnetic conductivity of the deposits, their electromagnetic shielding effect values were calculated and the influence of cobalt on the corrosion and electromagnetic shielding properties of Ni–Co–P deposits was revealed. The results showed that cobalt improved the corrosion resistance and greatly enhanced the electromagnetic shielding property of Ni–Co–P deposits. Electroless Ni–Co–P deposits on Al substrate would impart the product with high corrosion resistance, good electromagnetic shielding effect and light weight.