Aspects of material selection and innovative concepts of car construction using aluminium as best suited light-weight materials were presented, and recent development in established and advanced use of aluminium in passenger cars was discussed that help to meet economic and environmental requirements. 5xxx and 6xxx aluminium alloys were presented that have been improved for the increasing demands regarding higher strength and better formability, resulting in a mass reduction and improved crashworthiness. Furthermore, advances concerning multi-material light weight design were presented by examples for aluminium solutions in advanced “Multi-material” Super-Light-Car (SLC) concepts, which reaches significant mass reductions.
The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg(-Cu) system. They are widely used in high-performance structural aerospace and transportation applications. Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effects of homogenisation, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys. With a focus on recent work at Monash University, where the whole processing route from homogenisation to final ageing has been studied for thick plate products, it is reported how microstructural features such as dispersoids, coarse constituent particles, fine-scale precipitates, grain structure and grain boundary characteristics can be controlled by heat treatment to achieve improved microstructure–property combinations. In particular, the paper presents methods for dissolving unwanted coarse constituent particles by controlled high-temperature treatments, quench sensitivity evaluations based on a systematic study of continuous cooling precipitation behaviour, and ageing investigations of one-, two- and three-step ageing treatments using experimental and modelling approaches. In each case, the effects on both the microstructure and the resulting properties are discussed.
Hybrid metal matrix composites are important class of engineering materials used in automotive, aerospace and other applications because of their lower density, higher specific strength, and better physical and mechanical properties compared to pure aluminium. The mechanical and wear properties of hybrid aluminium metal matrix composites were investigated. Mica and SiC ceramic particles were incorporated into Al 356 alloy by stir-casting route. Microstructures of the samples were studied using scanning electron microscope (SEM). The chemical composition was investigated through energy dispersive X-ray (EDX) detector. The results indicate that the better strength and hardness are achieved with Al/10SiC-3mica composites. The increase in mass fraction of mica improves the wear loss of the composites.
The mechanical and tribological properties of hot-pressed copper-based composites containing different amounts of graphene nanosheets (GNSs) are compared with those of copper–graphite (Gr) composites fabricated by the same method. The results show that the Cu–GNSs composites exhibit higher relative density, microhardness and bending strength compared with Cu–Gr composites with the same volume fraction of GNSs and Gr. Moreover, the friction coefficients and wear rates reduce significantly by the addition of GNSs, whereas the limited impact on reducing friction and wear is found on graphite. The abrasive and delamination wear are the dominant wear mechanisms of the composites. It is believed that the superior mechanical and tribological performances of Cu–GNSs composites are attributed to the unique strengthening effect as well as the higher lubricating efficiency of graphene nanosheets compared with those of graphite, which demonstrates that GNS is an ideal filler for copper matrix composites, acting as not only an impactful lubricant but also a favorable reinforcement.
Stress corrosion cracking (SCC) is degradation of mechanical properties under the combined action of stress and corrosive environment of the susceptible material. Out of eight series of aluminium alloys, 2xxx, 5xxx and 7xxx aluminium alloys are susceptible to SCC. Among them, 7xxx series aluminium alloys have specific application in aerospace, military and structural industries due to superior mechanical properties. In these high strength 7xxx aluminium alloys, SCC plays a vital factor of consideration, as these failures are catastrophic during the service. The understanding of SCC behaviour possesses critical challenge for this alloy. The main aim of this review paper is to understand the effect of constituent alloying elements on the response of microstructural variation in various heat-treated conditions on SCC behavior. Further, review was made for improving the SCC resistance using thermomechanical treatments and by surface modifications of 7xxx alloys. Apart from a brief review on SCC of 7xxx alloys, this paper presents the effect of stress and pre-strain, effect of constituent alloying elements in the alloy, and the effect of environments on SCC behaviour. In addition, the SCC behaviours of weldments, 7xxx metal matrix composites and also laser surface modifications were also reviewed.
Modified potential ecological risk index (MRI) was proposed based on the potential ecological risk index (RI) and risk assessment code (RAC) by modifying an index. The modified index was relevant to the chemical speciation of heavy metals. Xiawan Port, a typical region contaminated by industrial production, was selected as a case study area. The total concentrations and chemical speciation of heavy metals in sediments of Xiawan Port were analyzed. The experimental data indicate that Xiawan Port is seriously polluted by heavy metals, especially by Cd. The risks of heavy metals are evaluated by RI, RAC and MRI, respectively. The resluts of MRI show that the risks of heavy metals are in the decreasing order of Cd>Pb>Cu>Zn. Comparison of results by different methods reveals that MRI integrates the characters of RI and RAC. MRI is recognized to be useful for risk managemnt of heavy metals in sediments.
Cu-doped TiO nanoparticles with different doping contents from 0 to 2.0% (mole fraction) were synthesized through sol–gel method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscope (FE-SEM) were used to characterize the crystalline structure, chemical valence states and morphology of TiO nanoparticles. UV–Vis absorption spectrum was used to measure the optical absorption property of the samples. The photocatalytic performance of the samples was characterized by degrading 20 mg/L methyl orange under UV–Vis irradiation. The results show that the Cu-doped TiO nanoparticles exhibit a significant increase in photocatalytic performance over the pure TiO nanoparticles, and the TiO nanoparticles doped with 1.0% Cu show the best photocatalytic performance. The improvement in photocatalytic performance is attributed to the enhanced light adsorption in UV–Vis range and the decrease of the recombination rate of photoinduced electron–hole pair of the Cu-doped TiO nanoparticles.
Stir casting was used to produce AA6061/15%TiC (mass fraction) aluminum matrix composites (AMCs). An empirical relationship was developed to predict the effect of stir casting parameters on the ultimate tensile strength (UTS) of AA6061/TiC AMCs. A central composite rotatable design consisting of four factors and five levels was used to minimize the number of experiments, i.e., castings. The factors considered were stirring speed, stirring time, blade angle and casting temperature. The effect of those factors on the UTS of AA6061/TiC AMCs was derived using the developed empirical relationship and elucidated using microstructural characterization. Each factor significantly influenced the UTS. The variation in the UTS was attributed to porosity content, cluster formation, segregation of TiC particles at the grain boundaries and homogenous distribution in the aluminum matrix.
Aluminum was leached out from coal fly ash by pressure acid-leaching method. The effects of coal fly ash size, sulfuric acid concentration, reaction time and reaction temperature on extraction efficiency of aluminum were investigated comprehensively. The phase and morphology of coal fly ash and solid residues after reaction were analyzed by XRD, SEM and IR. The optimal technological conditions for extracting aluminum from coal fly ash were eventually confirmed that coal fly ash with size of 74 μm and sulfuric acid with concentration of 50% are mixed in pressure reaction kettle to react for 4 h at 180°C. Under the optimal conditions, the extraction efficiency of aluminum can reach 82.4%.
The effect of reinforcement on the wear mechanism of metal matrix composites (MMCs) was investigated by considering different parameters, such as sliding distance (6 km), pressure (0.14–1.1 MPa) and sliding speed (230–1480 r/min). The wear mechanisms of an MMC and the corresponding matrix material under similar experimental conditions were compared on a pin-on-disc wear machine. The pins were made of 6061 aluminum matrix alloy and 6061 aluminum matrix composite reinforced with 10% Al O (volume fraciton) particles (6–18 μm). The disc was made of steel. The major findings are as follows: the MMC shows much higher wear resistance than the corresponding matrix material; unlike that of matrix material, the wear of MMC is very much linear and possible to predict easily; the wear mechanism is similar for both materials other than the three-body abrasion in the case of MMC; the reinforced particles resist the abrasion and restrict the deformation of MMCs which causes high resistance to wear. These results reveal the roles of the reinforcement particles on the wear resistance of MMCs and provide a useful guide for a better control of their wear.
Bauxite residue, a highly saline solid waste produced from digestion of bauxite for alumina production, is hazardous to the environment and restricts vegetation establishment in bauxite residue disposal areas. A novel water leaching process proposed here was used to investigate the dynamic migration and vertical distribution of saline ions in bauxite residue. The results show that water leaching significantly reduced the salinity of bauxite residue, leaching both saline cations Na , K , Ca and anions CO , SO , HCO . Na and K migrated from 40–50 to 20–30 cm of the column, presenting a high migration capacity. The migration capacity of Ca was lower and accumulated at 30–40 cm of the column. CO initially distributed at 20–30 cm of the column, subsequently transported to 30–40 cm of the column, and finally returned to 20–30 cm of the column along with evaporation. SO was originally distributed at 40–50 cm, but finally migrated to 20–30 cm of the column. Nevertheless, HCO remained at the bottom of the column, and its migratory was less affected by evaporation.
Static mechanical experiments were carried out on granite after and under different temperatures using an electro-hydraulic and servo-controlled material testing machine with a heating device. Variations in obvious form, stress-strain curve, peak strength, peak strain and elastic modulus with temperature were analyzed and the essence of rock failure modes was explored. The results indicate that, compared with granite after the high temperature treatment, the brittle-ductile transition critical temperature is lower, the densification stage is longer, the elastic modulus is smaller and the damage is larger under high temperature. In addition, the peak stress is lower and the peak strain is greater, but both of them change more obviously with the increase of temperature compared with that of granite after the high temperature treatment. Furthermore, the failure modes of granite after the high temperature treatment and under high temperature show a remarkable difference. Below 100 °C, the failure modes of granite under both conditions are the same, presenting splitting failure. However, after 100 °C, the failure modes of granite after the high temperature treatment and under high temperature present splitting failure and shear failure, respectively.
Bismuth molybdate (Bi MoO ) nano-particles (NPs) were synthesized using bismuth nitrate, ammonium molybdate, citric acid and ethyl cellulose by a simple sol–gel method. The structure, morphology, opto-magnetic and photocatalytic properties of the obtained powder were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, high resolution scanning electron microscopy (HRSEM), energy dispersive X-ray (EDX), ultraviolet–visible diffuse reflectance spectra (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM) techniques. The XRD, FT-IR and EDX results indicate that the resultant powder is pure and single phase crystalline Bi MoO with orthorhombic structure. The HRSEM image shows that the morphology of obtained powder consists with well defined nano-particles structure. The VSM results show superparamagnetic behavior of the obtained nano-particles. The photocatalytic activity of Bi MoO nano-particles was performed. The addition of TiO catalyst enhances the photocatalytic activity of Bi MoO nano-particles. The catalysts Bi MoO , TiO and mixed oxide catalyst Bi MoO –TiO nano-composites (NCs) were tested for the photocatalytic degradation (PCD) of 4-chlorophenol (4-CP). It is found that the PCD efficiency of Bi MoO –TiO NCs is higher than that of pure Bi MoO and TiO catalysts.
Magnesium phosphate conversion coating (MPCC) was fabricated on AZ31 magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg and PO ions. The MPCC on AZ31 Mg alloy showed micro-cracks structure and a uniform thickness with the thickness of about 2.5 µm after 20 min of phosphating treatment. The composition analyzed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the coating consisted of magnesium phosphate and magnesium hydroxide/oxide compounds. The MPCC showed a significant protective effect on AZ31 Mg alloy. The corrosion current of MPCC was reduced to about 3% of that of the uncoated surface and the time for the deterioration process during immersion in 0.5 mol/L NaCl solution improved from about 10 min to about 24 h.
The strength of rock materials is largely affected by water and loading conditions, but there are few studies on mechanical properties of saturated rocks at high strain rates. Through compressive tests on dry and saturated sandstone specimens, it was found that the dynamic compressive strength of both dry and saturated sandstone specimens increased with the increase of strain rates. The saturated rock specimens showed stronger rate dependence than the dry ones. The water affecting factor (WAF), as the ratio of the strength under dry state to that under saturated state, was introduced to describe the influence of water on the compressive strength at different strain rates. The WAF under static load was close to 1.38, and decreased with the increase of strain rate. When the strain rate reached 190 s , the WAF reduced to 0.98. It indicates that the compressive strength of saturated specimens can be higher than that of dry ones when the strain rate is high enough. Furthermore, the dual effects of water and strain rate on the strength of rock were discussed based on sliding crack model, which provided a good explanation for the experimental results.
The microstructure and mechanical properties of nano composites processed via stir casting were studied. The composites were based on the A356 aluminum alloy reinforced with nano SiC particles. The density measurements show that the samples contain little porosity and the amount of porosity in the composites increases with increasing volume fraction of SiC. The microstructures of the composites were examined using optical microscope and transmission electron microscope. Microscopic observations of the microstructures reveal that the dispersion of the particles is uniform. The yield strength, ultimate tensile strength and the elastic modulus are improved with the addition of nano particles although some reduction in ductility is observed. The highest yield strength and ultimate tensile strength are obtained with the addition of 3.5% SiC nano-particles. A relatively ductile fracture in tensile fractured samples was observed by fractography examination.
Friction stir welding (FSW) is a solid-state welding process which is capable of joining materials which are relatively difficult to be welded by fusion welding process. Further, this process is highly energy-efficient and environmental-friendly as compared to the fusion welding. Despite several advantages of FSW over fusion welding, the thermal cycles involved in FSW cause softening in joints generally in heat-treatable aluminum alloys (AAs) due to the dissolution or coarsening of the strengthening precipitates leading to decrease in mechanical properties. Underwater friction stir welding (UFSW) can be a process of choice to overcome these limitations. This process is suitable for alloys that are sensitive to heating during the welding and is widely used for heat-treatable AAs. The purpose of this article is to provide comprehensive literature review on current status and development of UFSW and its importance in comparison to FSW with an aim to discuss and summarize different aspects of UFSW. Specific attention is given to basic principle including material flow, temperature generation, process parameters, microstructure and mechanical properties. From the review, it is concluded that UFSW is an improved method compared with FSW for improving joint strength. Academicians, researchers and practitioners would be benefitted from this article as it compiles significantly important knowledge pertaining to UFSW.
Cathode material of spent lithium-ion batteries was refined to obtain high value-added cobalt and lithium products based on the chemical behaviors of metal in different oxidation states. The active substances separated from the cathode of spent lithium-ion batteries were dissolved in H SO and H O solution, and precipitated as CoC O ·2H O microparticles by addition of (NH ) C O . After collection of the CoC O ·2H O product by filtration, the Li CO precipitates were obtained by addition of Na CO in the left filtrate. The experimental study shows that 96.3% of Co (mass fraction) and 87.5% of Li can be dissolved in the solution of 2 mol/L H SO and 2.0% H O (volume fraction), and 94.7% of Co and 71.0% of Li can be recovered respectively in the form of CoC O ·2H O and Li CO .
experiments for five groups of homogeneous sandstone under different freeze–thaw cycles were conducted. After freeze– thaw, nuclear magnetic resonance (NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze–thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze–thaw and thawing. Dynamic compressive stress–strain curve of sandstone undergoing freeze–thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze–thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.
Functionally graded Al/B C, Al/SiC, Al/Al O and Al/TiB composites with constant 12% (mass fraction) of reinforcement were fabricated by centrifugal casting and hollow cylindrical components were obtained. Microstructural characteristics were investigated at outer surface of all composites and segregation of reinforcement particles was observed. Graded property of the composites with different reinforcements was investigated through hardness and tensile measurements. Results revealed that the outer peripheries of all composites exhibit higher hardness except in Al/B C composite and the outer zones of all composites show higher tensile strength. Abrasive wear test was conducted on the outer peripheries of all composites and Al/TiB composite exhibits less wear rate.