The effects of non-flux purification techniques on the mechanical properties and microstructure of AZ91 magnesium alloy were investigated by ICP, OM, XRD and SEM. The results show that Ar spraying with high flow rate could remove non-metallic inclusions and improve the mechanical properties of AZ91. The alloy obtains the best properties after argon spraying for 30 min at the melt temperature of 740 °C. The ceramic foam filter (CFF) could effectively improve the ultimate tensile strength and elongation of AZ91 alloy, especially the elongation, which increase with increasing pores per inch (ppi) and the thickness of CFF. Non-flux purification does not change the microstructure of AZ91 alloy. However, filtration has a certain effect on the fracture pattern of AZ91 alloy. To improve the mechanical properties effectively, both filtration and gas spraying should be utilized together.

The working principle of LFEC(Low frequency electromagnetic casting) process developed in Northeastern University, China was introduced and the metallurgical results of LFEC were discussed according to the casting practices. The low frequency field around the mold produces Lorenz force, which can be divided into two parts: one is the potential force which will be balanced by a pressure gradient of the liquid and results in the formation of a convex surface meniscus and improves the surface quality; the other is the rotary force which stirs the liquid in the mold to refine the microstructures and homogenize the distribution of alloying elements. LFEC can refine microstructures remarkably, improve surface quality of the ingots, depress macrosegregation and eliminate cracks. Some new technologies, such as horizontal direct chill casting under low-frequency electromagnetic field (HLEC), DC casting of hollow billets under electromagnetic fields (HBEC), electromagnetic modifying of hypereutectic Al-Si alloys(EMM), air film casting under static magnetic field (AFCM), and multi-ingots casting under low-frequency magnetic field (MLFEC) were developed based on LFEC.

Deformation twins and stacking faults were observed in nanostructure Al-Mg alloys subjected to high pressure torsion. These observations are surprising because deformation twinnings have never been observed in their coarse-grained counterparts under normal conditions. Experimental evidences are introduced on non-equilibrium grain boundaries, deformation twinnings and partial dislocation emissions from grain boundaries. Some of these features can be explained by the results reported from molecular-dynamics simulations of pure FCC metals. Special emphasis is laid on the recent observations of high density hexagonal and rhombic shaped nanostructures with an average size of 3 nm in the Al-Mg alloys processed by high pressure torsion. A possible formation process of these nanostructures is proposed based on molecular-dynamics simulations.

With the global warming of concern, the secondary aluminum stream is becoming an even more important component of aluminum production and is attractive because of its economic and environmental benefits. In this work, recycling of automotive aluminum is reviewed to highlight environmental benefits of aluminum recycling, use of aluminum alloys in automotive applications, automotive recycling process, and new technologies in aluminum scrap process. Literature survey shows that newly developed techniques such as laser induced breakdown spectroscopy (LIBS) and solid state recycling provide promising alternatives in aluminum scrap process. Compared with conventional remelting and subsequent refinement, solid state recycling utilizing compression and extrusion at room or moderate temperature can result in significant energy savings and higher metal yield.

Element parameters including volume filled ratio, surface dimensionless distance, and surface filled ratio for DFDM (direct finite difference method) were proposed to describe shape and location of free surfaces in casting mold filling processes. A mathematical model of the filling process was proposed specially considering the mass, momentum and heat transfer in the vicinity of free surfaces. Furthermore, a method for gas entrapment was established by tracking flow of entrapped gas. The model and method were applied to practical ADC1 high pressure die castings. The gas entrapment prediction was compared with the fraction and maximum size of porosities in the different casting parts. The comparison shows validity of the proposed model and method. The study indicates that final porosities in high pressure die castings are dependent on both gas entrapment during mold filling process and pressure transfer within solidification period.

Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test. Total elongation increases with temperature up to 250 °C, but uniform elongation and maximum expansion ratio get the highest value at 175 °C. Different axial feeding amounts were applied in experiments to determine the reasonable loading path. A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed. Finally, mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.

Characterizations of phases in Mg-10%Y-5%Gd-2%Zn-0.5%Zr (WGZ1052) alloy during heat treatments were investigated by OM, XRD, SEM and EDS. The mechanisms of microstructure evolution were discussed. The results show that, after high temperature heat treatments, the Mg₁₂ZnY phases still exist. During solution-treatment at 535 °C, the amount of the long-period stacking order structures decreases. At 545 °C for 20 h and 24 h, there are still remnant Mg₁₂ZnY compounds in the Mg matrix, the shape of which does not change and the amount does not decrease obviously.

The microstructure and crystallographic texture characteristics of an extruded ZK60 Mg alloy subjected to cyclic extrusion and compression (CEC) up to 8 passes at 503 K were investigated. The local crystallographic texture, grain size and distribution, and grain boundary character distributions were analyzed using high-resolution electron backscatter diffraction (EBSD). The results indicate that the microstructure is refined significantly by the CEC processing and the distributions of grain size tend to be more uniform with increasing CEC pass number. The fraction of low angle grain boundaries (LAGBs) decreases after CEC deformation, and a high fraction of high angle grain boundaries (HAGBs) is revealed after 8 passes of CEC. Moreover, the initial fiber texture becomes random during CEC processing and develops a new texture.

Twin roll cast ZK60 alloy strip/sheet with final thickness of 0.5 mm was prepared, and effect of rolling temperature on microstructure and texture development was investigated using OM and XRD technique, microstructure and texture were measured on specimens subjected to rolling experiment at different rolling temperature, and macrotexture was also evaluated by X-ray diffraction method. In addition, the and (0002) pole figures were measured, and the tensile test was performed to reveal the influence of rolling temperature on mechanical properties. The results show that the microstructure of ZK60 alloy sheet consisted of fibrous structure with elongated grains, and shear bands along the rolling direction after warm rolling. Dynamic recrystallization could be found during the warm rolling process at rolling temperature 350 °C and above. And many fine recrystallized grain could be observed in the shear bands area. It is a little difficult to see the recrystallized grain in the sheet warm rolled at 300 °C because of higher density of shear bands. The warm rolled ZK60 alloy sheet exhibited strong (0002) pole texture, the intensity of (0002) pole figure decreases with the increasing of rolling temperature and the basal pole tilted slightly to the transverse direction after warm rolling.

Effects of ball-milling parameter on structures and properties of sintered Mg-1.5Zr (mass fraction, %) alloy were researched by metallographic analysis, mechanical properties tests and DMA technology. The results indicate that with 310 r/min rotation speed, the microstructure of the sintered alloy is greatly refined, and Zr-phase distributes uniformly. The micro-hardness, bending strength and damping capacities are the greatest under 310 r/min rotation speed. The damping peak of sintered Mg-1.5Zr alloy increases with increasing frequency under the testing conditions. The relaxation time meets the Arrhenius relationship, and shows the characteristics of relaxation damping.

In situ (Mg₂Si+MgO)/Mg composites fabricated from AZ91-Al₂(SiO₃)₃ under high-energy ultrasonic field were investigated by XRD, DSC and SEM. The results indicate that the size, morphology and distribution of the in situ Mg₂Si particles are greatly optimized with the assistance of the high-energy ultrasonic field. The amounts of the in situ Mg₂Si particles are increased, the sizes are refined, the distributions become uniform, and the morphologies are changed to smooth olive-shape or spherical shape. The amounts of brittle β-Mg₁₇Al₁₂ phases are decreased and the morphologies are granulated. The values of the tensile strength σ_b and HB hardness are increased. These are due to the cavitation effects and acoustic streaming effects induced by the high-energy ultrasonic field.

Recent new technology developments were presented in the field of industrial bending operations, including flexible stretch forming and 3D rotary stretch forming. Attempts were made to give an overview of different mechanisms that influence dimensional accuracy, including local cross-sectional deformations such as suck-in and volume conservation effects, along with global deformations such as springback. An analytical model was developed to determine the particular influence of different material, geometry and process parameters on dimensional variability of bent components. The results were discussed in terms of overall process capability (C_p) and associated process windows. The results show that different governing mechanisms prevail in various bending operations, meaning that attention has to be placed on controlling those process parameters that really are important to part quality in each specific case. Several strategies may be defined for reducing variability. One alternative may be to design more robust process and tool technology that reduce the effect of upstream parameters on dimensional variability of the formed part. The results show that optimal tool design and technology may in specific cases improve the dimensional accuracy of a formed part. Based on the findings discussed herein, it is concluded that advances in industrial bending operations require focus on improving the understanding of mechanical mechanisms, including models and parameter development, new technology developments, including process, tool, measurement and control capabilities, and process discipline at the shop floor, combined with a basic philosophy of controlling process parameters rather than part attributes.

As the competition from companies in low cost countries increases, the need for more automated production which reduces labour cost while improving product quality is required. A new rotary compression bending set-up with automated closed-loop feedback control is thus being developed. By transferring in-process measurement data into an algorithm for predicting springback and bend angle prior to the unloading sequence, the dimensional accuracy is improved. This work focuses on the development of this steering model. Since the method used does not increase cycle time, it is attractive for high-volume industrial applications. More than 150 bending tests of AA6060 extrusions were conducted to determine the capability of the technology. The results show that by activating the automated closed-loop feedback system, the dimensional accuracy of the bent parts is more than three times better than that obtained by traditional compression bending. Since the steering model permits the direct use of additional process data, such as instant wall thickness and cross sectional distortions, it is believed that extension of the measurement capabilities would improve the accuracy of the methodology even further.

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.

The effects of heat treatment process on microstructure, micro-yield strength and dynamic dimensional stability of ZL114A aluminum alloy were investigated by optical microscopy (OM), transmission electron microscopy (TEM), tensile testing and thermal cycling on-line measuring method. Fine dispersed eutectic Si phases are observed, and long strip eutectic Si and massive primary Si phases decrease in ZL114A alloy after high-temperature and long-time solution treatment, which result in the increase of micro-plastic deformation resistance. With the increasing of aging temperature, aging precipitation behaviour of ZL114A alloy transforms from precipitation of GP zone and β′ phases simultaneously at lower temperature to precipitation of stable Mg₂Si phases at higher temperature. Because coherent strengthening is the main strengthen mechanism for micro-plastic deformation, precipitation of stable Mg₂Si phases is unfavorable to the improvement of micro-plastic deformation resistance. Micro-yield strength cannot characterize dimensional stability comprehensively, and dynamic dimensional stability under alternative temperature should also be tested cooperatively for better evaluation of dimensional stability.

Aluminum matrix composites reinforced by in situ Al₂O₃ and Al₃Zr particles are fabricated from A356-Zr(CO₃)₂ system via magnetochemistry reaction, and the morphologies, sizes and distributions of the in situ particles as well as the microstructures, mechanical mechanisms of the composites are investigated by XRD, SEM, TEM and in situ tensile tests. The results indicate that with the pulsed magnetic field assistance, the morphologies of the in situ particles are mainly with ball-shape, the sizes are in nanometer scale and the distributions in the matrix are uniform. The interfaces between the in situ particles and the aluminum matrix are net and no interfacial outgrowth is observed. These are due to the strong vibration induced by the applied magnetic field in the aluminum melt, which in turn, accelerates the melt reactions. The effects of the magnetic field on the above contributions are discussed in detail.

The Al-Si alloy with high Si content was prepared by pressure infiltration. Microstructure observation shows that three-dimensional structure (3D-structure) is obtained from irregular sharp Si particles via high temperature diffusion treatment (HTDT). Flat Si-Al interfaces transform to smooth curves, and Si phases precipitate in Al and Si-Al interface. The bonding of Si-Al interface is improved by HTDT, which improves the mechanical performance of Al-Si alloy. The bending strength of 3D-Al-Si alloy increases by 6% compared with that of Al-Si alloy, but the elastic modulus changes a little. The coefficient of thermal expansion (CTE) of the 3D-Al-Si alloy is 7.7×10⁻⁶/°C from 20 °C to 100 °C, which decreases by 7% compared with that of Al-Si alloy. However, HTDT has little effect on the thermal conductivity of Al-Si alloy.

Ultrafine grain pure aluminum was produced by equal channel angular pressing and cold rolling, the deformed aluminum was annealed at 200 °C for 1 h. The tensile curves of deformed and annealed aluminum show that yield strength of deformed aluminum increases by 100%−300% and its elongation decreases by about 20%. After low temperature annealing, strength of annealed aluminum increases by 20% and elongation decreases by over 50%, the recovery of dislocations may be the main cause of annealing strengthening. In addition, there is an abrupt stress drop in the tensile curves of annealed aluminum and the formation of shear band is responsible for it.

Two micron SiC particles with angular and spherical shape and the sub-micron Al₂O₃ particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology. Microstructures and effect of thermal-cooling cycle treatment (TCCT) on the thermal expansion behaviors of three composites were investigated. The results show that the composites are free of porosity and SiC/Al₂O₃ particles are distributed uniformly. Inflections at about 300 °C are observed in coefficient of thermal expansion (CTE) versus temperature curves of two SiC_p/Al composites, and this characteristic is not affected by TCCT. The TCCT has significant effect on thermal expansion behavior of SiC_p/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles. However, no inflection is observed in Al₂O_3p/Al composite, while TCCT has effect on CTE of Al₂O_3p/Al composite. These results should be due to different relaxation behavior of internal stress in three composites.

Two kinds of unidirectional PAN M40 carbon fiber (55%, volume fraction) reinforced 6061Al and 5A06Al composites were fabricated by the squeeze-casting technology and their interface structure and thermal expansion properties were investigated. Results showed that the combination between aluminum alloy and fibers was well in two composites and interface reaction in M40/5A06Al composite was weaker than that in M40/6061Al composite. Coefficients of thermal expansion (CTE) of M40/Al composites varied approximately from (1.45−2.68)×10⁻⁶ K⁻¹ to (0.35−1.44)×10⁻⁶ K⁻¹ between 20 °C and 450 °C, and decreased slowly with the increase of temperature. In addition, the CTE of M40/6061Al composite was lower than that of M40/5A06Al composite. It was observed that fibers were protruded significantly from the matrix after thermal expansion, which demonstrated the existence of interface sliding between fiber and matrix during the thermal expansion. It was believed that weak interfacial reaction resulted in a higher CTE. It was found that the experimental CTEs were closer to the predicted values by Schapery model.

Consumable carbon anodes are used in the electrowinning of aluminium by the Hall-Heroult process. Emissions of CO₂ may be eliminated by introducing an inert oxygen evolving anode, which however will require a higher anode potential. An alternative approach is to use a natural gas or hydrogen gas anode to reduce the CO₂ emissions and lower the anode potential. Preliminary laboratory experiments were carried out in an alternative molten salt electrolyte consisting of CaCl₂-CaO-NaCl at 680 °C. Porous anodes of platinum and tin oxide were tested during electrolysis at constant current. The behaviour of inert anode candidate materials such as tin oxide and nickel ferrite were also studied.

In 2008, around 596 000 t of aluminum dross was generated from secondary aluminum industry in China; however, it was not sufficiently recycled yet. Approximately 95% of the Al dross was land filled without innocent treatment. The purpose of this work is to investigate Al dross recycling by environmentally efficient and friendly methods. Two methods of Al dross recycling which could utilize Al dross efficiently were presented. High-quality aluminum-silicon alloys and brown fused alumina (BFA) were produced successfully by recycling Al dross. Then, life cycle assessment (LCA) was performed to evaluate environmental impact of two methods of Al dross recycling process. The results show that the two methods are reasonable and the average recovery rate of Al dross is up to 98%. As the LCA results indicate, they have some advantages such as less natural resource consumption and pollutant emissions, which efficiently relieves the burden on the environment in electrolytic aluminum and secondary aluminum industry.

In order to establish the rolling process parameters of grade-2 commercially pure titanium (CP-Ti), it is necessary to understand the transformation mechanism and mechanical properties of this material. The β→α transformation kinetics of the grade-2 CP-Ti during continuous cooling was measured and its hot compression behavior was investigated using Gleeble-1500 thermal mechanical simulator. Dynamic CCT diagram confirms that cooling rate has an obvious effect on the start and finishing transformation and microstructures at room temperature. The critical cooling rate for β-phase transforms to α phase is about 15 °C/s. When the cooling rate is higher than 15 °C/s, some β phases with fine granular shape remain residually into plate-like structure. The plate-like α phase forms at cooling rate lower than 2 °C/s, serrate α phase forms at medium cooling rates, about 5−15 °C/s. The flow stress behavior of grade-2 CP-Ti was investigated in a temperature range of 700−900 °C and strain rate of 3.6−40 mm/min. The results show that dynamic recrystallization, dynamic recovery and work-hardening obviously occur during hot deformation. Constitutive equation of grade-2 CP-Ti was established by analyzing the relationship of the deformation temperature, strain rate, deformation degree and deformation resistance.

Isothermal compression tests are applied to study the deformation mechanisms of TC11 titanium alloy with lamellar structure under the deformation temperature range of 890−995 ^oC and strain rate range of 0.01−10 s⁻¹. According to the flow stress data obtained by compression tests, the deformation activations are calculated based on kinetics analysis of high temperature deformation, which are then used for deformation mechanism analysis combined with microstructure investigation. The results show that deformation mechanisms vary with deformation conditions: at low strain rate range, the deformation mechanism is mainly dislocation slip; at low temperature and high strain rate range, twinning is the main mechanism; at high temperature and high strain rate range, the deformation is mainly controlled by diffusion of β phase.

Thermo-mechanical fatigue tests were carried out on the gamma-TiAl alloy in the temperature range of 500−800 °C under mechanical strain control in order to evaluate its cyclic deformation behaviors at elevated temperature. Cyclic deformation curves, stress−strain hysteresis loops under different temperature−strain cycles were analyzed and dislocation configurations were also observed by TEM. The mechanisms of cyclic hardening or softening during thermo-mechanical fatigue (TMF) tests were also discussed. Results showed that thermo-mechanical fatigue lives largely depended on the applied mechanical strain amplitudes, applied types of strain and temperature. On the hysteresis loops appeared two apparent asymmetries: one was zero asymmetry and the other was tensile and compressive asymmetry. Dislocations configuration and slip behaviors were contributed to cyclic hardening or cyclic softening.

The hot deformation behavior of Ti-6Al-4V (TC4) titanium alloy was investigated in the temperature range from 650 °C to 950 °C with the strain rate ranging from 7.7×10⁻⁴ s⁻¹ to 7.7×10⁻² s⁻¹. The hot tension test results indicate that the flow stress decreases with increasing the deformation temperature and increases with increasing the strain rate. XRD analysis result reveals that only deformation temperature affects the phase constitution. The microstructure evolution under different deformation conditions was characterized by TEM observation. For the deformation of TC4 alloy, the work-hardening is dominant at low temperature, while the dynamic recovery and dynamic re-crystallization assisted softening is dominant at high temperature.

The physical characteristics and microstructure of the fluoride film formed during activation were investigated using SEM, XPS and SAM, and its stability in electroless nickel (EN) bath was analyzed. The effects of the fluoride film on EN deposition were studied additionally. The results show that the fluoride film on magnesium alloys is a kind of porous film composed of MgF₂ with thickness of 1.6−3.2 μm. The composition of the activation bath and pretreatment of EN processing have influence on the composition of the fluoride film. The fluoride is stable and dissolves little in EN bath; as a result, the fluoride film can protect magnesium substrate from the corrosion of EN bath. The composition of fluoride determines the initial deposition of EN and part of the fluoride film finally exists as inclusion in EN coating.

Laser surface cladding was applied on a TC4 Ti alloy to improve its surface properties. Mixed TiC and Ti powders with a TiC-to-Ti mass ratio of 1:3 were put onto the TC4 Ti alloy and subsequently treated by laser beam. The microstructure and composition modifications in the surface layer were carefully investigated by using SEM, EDX and XRD. Due to melting, liquid state mixing followed by rapid solidification and cooling, a layer with graded microstructures and compositions formed. The TiC powders were completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The inter-dendritic areas were filled with fine α′ phase lamellae enrich in Al. Mainly due to the reduced TiC volume fraction with increasing depth, the hardness decreases with increasing depth in the laser clad layer with a maximum value of HV1400, about 4.5 times of the initial one.

A Mg-6Zn-3Gd (mass fraction, %) alloy, noted as ZG63, was coated by different micro-arc oxidation (MAO) processes, and the coating structure and corrosion resistance of the alloy were studied using scanning electron microscopy (SEM), glancing angle X-ray diffractometry (GAXRD) and various electrochemical methods. The micro-arc oxidation process consists of three stages and corresponds with different coating structures. In the initial stage, the coating thickness is linearly increased and is controlled by electrochemical polarization. In the second stage, the coating grows mainly inward and accords with parabolic regularity. In the third stage, the loose coating forms and is controlled by local arc light. The looser coating is mainly composed of MgSiO₃ and the compact coating is mainly composed of MgO. From micro-arc oxidation stage to local arc light stage, the corrosion resistance of the coated alloy firstly increases and then decreases. The satisfied corrosion resistance corresponds to the coating time ranging from 6 to10 min.

The corrosion resistance of the micro-arc oxidation (MAO) ceramic coating on a cast Al-13Si-5Cu alloy was investigated using various electrochemical methods including electrochemical impedance spectroscopy (EIS) and polarization curves. Microstructures of MAO ceramic coating were studied by SEM, and the influence of microscopic patterns on corrosion resistance was analyzed. The corrosion resistance of the aluminum alloy can be improved significantly by MAO process owing to increasing impedance and corrosion potential and decreasing corrosion current, and the ceramic coatings are composed of loose layer, compact layer and transition layer, which improve the corrosion resistance. The corrosin resistance is determined by the thickness of the compact layer and is not proportional to the total thickness of MAO, though the latter is one of the important factors influencing the corrosin resistance.