The isothermal compression bonding deformation of 705/706 aluminum alloy laminated materials was carried out on Gleeble-3500 hot-simulation machine at 573~773 K and 0.01~10 s^-1.The hot bonding behavior and hot workability of the materials were analyzed,and the constitutive equation and processing map were established.The results show that in the process of compression deformation of the 705/706 aluminum alloy laminated materials,the flow stress is decreased with the increase of deformation temperature and increased with the increase of strain rate,exhibiting steady rheological characteristics when the flow stress reaches the peak value,so it is characterized by positive strain rate sensitivity. The deformation activation energy of the laminated materials is about 147.2 kJ/mol,which is lower than that of single Al-7.0Zn-2.9Mg alloy.The processing maps with different true strains show that safe deformation zone of 705 and 706 aluminum alloys bonding deformation is mainly attained at high cladding temperatures,moderate strains and low strain rates.The bonding strains range of 0.2~0.4,temperatures range of 723~748 K and the strain rates range of 0.1~0.01 s^-1 are appropriate for bonding deformation of the 705/706 aluminum alloy laminated materials.

The preparation technology and application of copper/aluminum composite were introduced.It was summarized for mechanism of interface combination,formation process of interfacial layer,the formation and growth rule of intermetallic compounds in interface layer and its effects on the physical and mechanical properties of composites.Finally,the research direction and development trend was proposed.

The interface bonding mechanism of bimetallic clad pipes was reviewed,and main preparation processes of bimetallic clad pipes at home and abroad were described systematically.According to the difference in the physical state of the substrate and cladding metal at the initial stage,the existing preparation processes are divided into four categories:solid-solid bonding method,solid-liquid bonding method, liquid-liquid bonding method and other bonding method.The forming principles and main characteristics of various preparation processes were analyzed comparatively.Finally,the prospects for the major issues that would be faced in the industrialization of bimetallic clad pipes were forecasted combined with the development status and future industrial application requirements.

Biodegradable magnesium alloys have good promising applications as biomaterials. Firstly, the main problems of biodegradable magnesium alloys as biomaterials were reviewed. Then, two methods including alloying and surface modification in improving the degradation resistance and biological activity of magnesium alloys were described. Besides, the recent progress in the magnesium alloys as biodegradable cardiovascular stent and bone repair materials were also introduced. Finally, the future development of biodegradable magnesium alloys was pointed out.

Rare earth element is widely used in a variety of metal materials due to the effective and stable modification.The modification can refine alloy structure,thus improving mechanical properties,and the modification effect of different rare earth elements on aluminum alloy is different.The influence of several rare earth elements on the microstructure and mechanical properties of aluminum alloys as well as the modification mechanism was mainly introduced.Meanwhile,the present research status of rare earth aluminum alloys at home and abroad was reviewed.The existing problems were discussed and the future research was prospected.

Wire and arc additive manufacturing(WAAM) is a technology for the rapid forming of large-scale metal components with complex structures, which has the advantages of low equipment cost, high material utilization and high deposition efficiency. On this basis, the current research status of WAAM equipment, materials and processes was highlighted combined with the hot topics of forming accuracy, microstructure characteristics and mechanical properties of metallic components. Finally, the key technologies that need to be solved for WAAM were summarized and the development direction of WAAM was prospected.

The segregation of Fe and Si in aluminum alloy castings was analyzed by optical microscope, scanning electron microscope and other equipment, and the influence of Fe and Si segregation on castings together with corresponding solutions were briefly described.

The micro-structure and mechanical characteristics of the multi-layer nickel-plated copper foil welding by blue light laser with 450 nm were investigated. Nickel-plated copper foil with 20 layers were welded onto nickel-plated copper sheet with 0.5 mm, and the effects of different welding speeds on the weld morphology and tensile strength were investigated. The morphology on the weld failure mode and the micro morphology of the fracture were analyzed, and the electrical conductivity of the weld were tested. The results indicate that during the blue laser welding process, the depth of penetration is easily controlled.With the increase of welding speed, the weld penetration depth is gradually decreased, and the tensile strength of the weld is increased at first and then decreased.When the welding speed is 30 mm/s, the tensile strength of the weld reaches the maximum of 75 MPa. Blue laser can be successfully applied to the welding of multi-layer nickel-plated copper foil and laser welding leads to good mechanical properties.

The failure of metal materials usually originates from the material surface. Through strengthening the material surface, the service life of metal components can be proloned and efficiency can be improved. High-entropy alloys (HEAs) attracts extensive attention due to the excellent corrosion resistance, wear resistance, high temperature oxidation resistance and other characteristics. The property diversity allows HEAs to be used as metal surface coating materials.Based on the existing research, the influence of HEAs coating on the surface properties of metal materials was comprehensively reviewed, and the performance characteristics of HEAs as coating as well as the preparation methods of HEAs coating were summarized. The problems and development trend of technology in HEAs coating field were put forward.

It was reviewed comparatively for the advantages and disadvantages of traditional electrical discharge machining (EDM), electron-chemical machining (ECM) and long pulsed laser processing on the hole wall quality, accuracy and efficiency of film cooling hole processing.Femtosecond laser provided a solution for high-quality film cooling hole processing.For femtosecond laser drilling, its "cold processing" characteristics and mechanism were described, and the basic theory of damage threshold and experimental calculation method were analyzed.At the same time, numerical calculation models and methods of femtosecond laser ablation mechanism were summarized. It is pointed out that the molecular dynamics method (MD) combined with the two-temperature model (TTM) is the quite promising for numerical simulation.

The characteristics and formation mechanism of surface defects such as cold shut,surface segregation layer,surface segregation burl and pull marks in semi-continuous casting aluminum alloy ingot were introduced.The effects of mold structure and casting process parameters on the surface defects during semi-continuous casting were analyzed.On this basis,the technical development and process optimization directions to improve ingot surface quality were presented.

The research status and progress of bulk amorphous alloy casting forming,and the principle and advantages-disadvantages of the preparation technology of bulk amorphous alloys were reviewed briefly,focusing on the copper mold casting,vacuum casting method and phase-changed refrigeration casting method.Some problems needing to be solved in casting process of bulk amorphous alloys were put forward.

In recent years, with the complexity of the gas-cooled structure and the large-scale size of the single-crystal turbine blade, the production of single-crystal blade is more prone to crystal selection failure, orientation deviation, sliver, large angle grain boundary, stray grain in the platform, recrystallization, freckles and other defects, which lead to the reduction of high-temperature alloy performance of single crystal turbine blade, and eventually cause the scrapping of single-crystal blade. In order to reduce these defects in single crystal blade, improve the quality of single crystal, and obtain a complete structure of single crystal structure, it is very important to be familiar with various common defects in the production of single crystal blade, realize the formation rules of defects, and master the defect inhibition technology. On this basis, the common solidification defects in the production of single crystal blades, as well as the formation rules and inhibition methods of solidification defects were systematically introduced, which lays a solid theoretical foundation for reducing the defects of single crystal blades and improving the quality and qualification rate of blades, and provides a strong technical support.

With the deeply understanding of the development of semi-solid metals(SSM)processing,the conception of "Generalized SSM" and "SSM +" were proposed.So called "Generalized SSM",indicating the melt on the liquidus temperature and the solid-liquid region via the high shearing of the melt and the forced uniform solidification to control nucleation and growth,is on the purpose of the structure refinement and the composition homogenization of the melt in nature,breaking the constraint of the composition of alloys."SSM +",based on the generalized SSM technology,is considered as a means of transforming the traditional processing technology."Generalized SSM" can be combined with liquid forming processes such as vertical semi-continuous casting,horizontal continuous casting,high pressure casting,extrusion casting,vacuum casting,etc.,and it also can be combined with deformation process such as forging,extrusion,rolling and so on.

The high quality integral forming of large-scale structural parts is a difficult problem in the field of parts manufacturing.Squeeze casting becomes a new choice for high-quality integral forming and manufacturing of large structural parts,which can successfully solve the problems of low feeding efficiency and shrinkage defects in traditional gravity casting by integral rheological feeding,and dramatically breaks through the limitation of equipment capacity in traditional forging technology by virtue of the good rheological filling capacity of molten metals.It has been proved that by using special coating and casting die instead of forging module and adjusting the die temperature effectively,they are efficient paths to reduce the cost proportion of die.Moreover,a series of new technologies,such as the local multi-point pressing,compound pressing and flowing semi-solid squeeze casting,are introduced to significantly reduce equipment investment and ensure high-quality forming.

Based on the research status of microbial corrosion of aluminum alloys in recent years, corrosion behavior and mechanism and achievements in the field of microbial corrosion protection, the process of representative bacteria and molds in microorganisms was attached and propagated on a variety of aluminum alloys, and their life activities causing or aggravating the corrosion was reviewed. The corrosion rate of aluminum alloy is controlled by microorganisms shielding, secrete corrosion inhibitors and metabolite inhibition. The microbial corrosion mechanism of aluminum alloy was mainly summarized, including cathodic depolarization mechanism, oxygen concentration cell mechanism, micro cell effect, corrosion compound formation, chloride induction and acid corrosion, as well as the mechanism of microbial inhibition of aluminum alloy corrosion. In conclusion, microbial corrosion of aluminum alloys is synergy of multiple corrosion mechanisms. Finally, the current methods to prevent and control microbial corrosion of aluminum alloys were described, and the research emphasis in the future was prospected, providing theoretical guidance for the prevention and control of microbial corrosion of aluminum alloys.

The damping mechanism,the materials system and reinforce microstructure of magnesium matrix damping composites were described.The preparation and post treatments of magnesium matrix damping composites were summarized.Based on the review and analysis of the research progress,the prospects of the developing directions of magnesium matrix damping composites were proposed.

The effects of different annealing temperature and time on the microstructural evolution and mechanical properties of the oxygen free copper tube were investigated by OM, TEM, SEM and universal tensile tester.The results reveal that:the high energy and high density dislocation of the as-deformed sample are evolved into thin dislocation walls, subgrain boundaries and then high angle grain boundaries with annealing at 260℃ or 300℃ for 60min, resulting in low density dislocation structure. After annealing at 300℃, recovery and recrystallization are fully completed.The tensile strength, yield strength and hardness are decreased with temperature increase, while the elongation is increased.Within the annealing temperature range of 300℃ to 460℃, the change of mechanical properties of the copper tube can be ignored.Increasing the annealing time at 300℃ from 10min to 60min, recrystallization is induced gradually, and the tensile strength, yield strength and hardness are decreased, while elongation is increased.With annealing for 60min, recrystallization is finished, and the tensile fracture morphology is changed from quasi-cleavage surface, tearing edge and dimple characteristics to equiaxial dimples. Compared with those of as-deformed sample, the tensile strength, yield strength and hardness of the copper tube are decreased by 39%, 68.5% and 53.1%, respectively, and the elongation is increased from 1.2% to 50%.With annealing time more than 60min, the grain size is increased slightly before reached a stable value, showing an insignificant effect on the mechanical properties.

7000 series high strength aluminum alloys have been widely used in aerospace field.However,due to its poor casting properties,the forming method is mainly adopted plastic deformation,such as rolling and extrusion.Forming products include mainly plates and profiles,while it is difficult to prepare parts with complex shapes.Liquid extrusion casting and semi-solid squeeze casting technology can provide a feasible approach for the casting and forming of 7000 series aluminum alloys and their composites.It is expected to achieve "casting instead of forging",becoming an important direction of the development of high strength aluminum alloy forming technology in recent years.The research progress in squeeze casting 7000 series aluminum alloys and their composites was described,and the current problems were presented.Then the development direction was pointed out.

Copper alloys have broad application prospects in the fields of marine engineering, transportation and aerospace.Due to the complex service environment, in addition to excellent mechanical properties, the corrosion resistance of copper alloys is also highly required.Therefore, the research status on electrochemical corrosion of copper alloys were reviewed, and influence law as well as mechanism of external environmental factors (temperature, pH value, etc.) and alloying elements (Fe, Mn, etc.) on the corrosion potential, corrosion current, corrosion types and corrosion products of copper alloys were emphasized in order to provide reference for the subsequent optimization of the corrosion resistance of copper alloys.

The recovery, separation, sorting and recycling of aluminum scrap is of practical significance to solve resource shortage, energy shortage and reduce environmental pollution.The development status of aluminum scrap recycles and resource allocation in domestic and overseas was introduced.The application and investigation of waste aluminum separation and sorting technologies in recent years were reviewed, and the advantages and disadvantages of these technologies in practical applications based on cost, efficiency and environmental impact were briefly summarized. Finally, the challenges and related countermeasures in the field of waste aluminum recycle, separation and sorting were analyzed, aiming to provide reference for scientific research, engineering application and development in related fields.

Aiming at the problems of misrun and coarse columnar crystal defects at the exhausting side of a K418B turbine guide under gravity investment casting, the centrifugal casting process was designed and simulated, and actual casting verification as well as grain size observation of the guide were carried out.The results show that the centrifugal casting process can improve effectively the filling capacity of the guide and eliminate the casting defects at the exhaust side.At the same time, under the action of centrifugal force field, fine equiaxed grains are formed in the blade during the solidification process, which fundamentally inhibits the formation of coarse columnar crystal defects and improves the comprehensive mechanical properties of the guide.

7075 aluminum alloy was prepared by permanent mold casting(PMC),liquid squeeze casting(LSC)and semi-solid squeeze casting(SSC)methods.The effects of different casting processes on the thermal conductivity and mechanical properties of 7075 aluminum alloy were investigated.The results indicate that the grains of the PMC are coarse,and dendrite segregation occurs to reduce the plastic toughness.The tensile strength and elongation are 121 MPa and 2.78%,respectively.However,the coarse grains exhibit a wide heat conduction path,lower electron scattering probability,long mean free path and relatively high thermal conductivity,which reaches139.67 W/(m·K).The tensile strength and elongation of the LSC refined grains are 239 MPa and 5.75%,respectively,while fine grains and more dendritic arms lead to the higher electronscattering,with the lowest thermal conductivity,which is 120.94 W/(m·K).SSC grains are compact fine and round,with the highest tensile strength and elongation of 248 MPa and 7.46%,respectively,and the thermal conductivity is 126.07 W/(m·K).

The optimized design of gating system for large-scale ring castings was completed by optimizing the structure,selecting the appropriate material and solidification shrinkage process parameters in combination with the FDM and FEM numerical simulation.The density of oxidized slagis decreases from(12~15)/cm² to(2~3)/cm²,and the average diameter is reduced from 2.6 mm to 0.4 mm after the graded melting and refining process.The average grain size is reduced from 176μm to 68μm,and the average tensile strength and elongation are increased about 8%~10% and 60% by selecting composite grain refinement,respeotively.The average tensile strength,yield strength and elongation of ZL114 A alloy reach 360 MPa,310 MPa and 8.2%,respectively,based on the multi-stage solid solution and aging process,While the corresponding values of ZL205 Aare 520MPa,460 MPa and 7.4%,and the fractures are characterized by typical dimple rupture.The internal residual stress is reduced from 140MPa~250 MPa to 50 MPa~105 MPa,and the machining accuracy of high and radial direction is increased about 180% after the cryogenic treatment.In addition the average tensile strength and elongation are increased by 20 MPa~30 MPa and 2%~3.5%,repectiuely,after the T6 treatment.

Eutectic high entropy alloys(EHEA), as one of the most potential high entropy alloys (HEAs) for industrial application due to the excellent comprehensive mechanical properties and desirable castability, have become a hot spot in the research field of high-entropy alloys. The latest research progress in the EHEAs was summarized, and the phase constitutes, microstructure, mechanical properties and methods of designing EHEAs were described in detail. Finally, the challenges of EHEAs were pointed out and the development direction of eutectic high entropy alloys was prospected.

The thickness of the solidified shell at different casting speeds was measured by the nail-shooting method. The solidification heat transfer model of the round billet was established and the growth curve of the solid shell was calculated.Based on the results of the nail-shooting experiment and the mathematical model,the optimized installation position of the final electromagnetic stirring(F-EMS)should be located at 10.23 m from the mold level.In consideration of plant conditions for the continuous casting of SWRH82B high carbon steel,the FEMS installation position was moved from 11.1 m to 9.75 m from the meniscus.The results show that after the process parameters optimization,the equiaxed crystal ratio in SWRH82B round billet is increased from 40%~46% before optimization to 50%~64%,and the central carbon segregation index is decreased from 1.08~1.10 before optimization to 1.04~1.06.The quality of continuous casting round billets has been improved significantly. Through tracking the quality of the rolled sheet,it is found that the network carbide in the SWRH82B wire rod is reduced,which indicates that the quality of the rolled sheet is improved greatly.

The 40Cr/Q345B bimetal was compressed and simulated by ABAQUS finite element software under different deformation temperature, strain rate and deformation. The changing law of equivalent strain, residual stress and temperature distributions in bimetal interface were analyzed, and the effects of deformation parameters on the composited interface were explored. The results indicate that the degree of interface recovery and recrystallization are increased at a higher temperature, which is beneficial to interface bonding, and the degree of interface bonding is enhanced with the deformation strain increasing. As the rate increases, the composited time is prolonged and interface reaction is sufficient, further strengthening the degree of interface bonding. By means of orthogonal tests, the optimum temperature of 1 150℃, strain rate of 0.1 s^-1 and strain of 65% are provided. The experimental results reveal that the element diffusion in bimetal interface is sufficient with a thickness of 22 μm, achieving desirable metallurgical bonding.

Based on the requirement of lightening for an electric vehicle structural part of the shock tower, influence of the aluminum design on weight-reduce was analyzed and a high vacuum die-casting process suitable for the aluminum alloy shock tower was developed.The results reveal that the rational mould design can decrease the weight of the shock tower by about 35% based on assemble, rigidity and die casting process.In addition, the reasonable design of the casting system and the control of the vacuum degree are the important factors affecting the stability of the air-gap and mechanical properties. Based on the analysis of bubble test and mechanical analysis, the design of ingate was optimized.The shock tower part can be achieved with tensile strength higher than 300MPa yield strength higher than 250MPa and the elongation higher than 8%, after T6heat treatment, meeting the requirement of OEM.

High-entropy alloy(HEA),which breaks the design concept of traditional alloy,is a new type of alloy composed of multiple main elements.However,most high-entropy alloys usually have poor fluidity and castability as well as larger compositional unevenness,which is adverse to the large-scale industrial application.Eutectic high-entropy alloys(EHEAs)exhibit the characteristics of high-entropy alloys and eutectic alloys simultaneously,which can reduce casting defects and have unique advantages in high-temperature application.Therefore,it is of great significance to design and preparation of eutectic high-entropy alloys.The research progress of melting eutectic high-entropy alloys at home and abroad was reviewed.The phase composition and properties of the alloys as well as the growth characteristics and mechanism of the eutectic morphology were introduced.Subsequently,the phase formation law of eutectic high-entropy alloy and the design method of eutectic composition were summarized.Finally,the forward research direction of eutectic high-entropy alloy was prospected.

6061-based metal matrix composites reinforced by 10% SiC particles with size of 20μm, 20μm+50μm and 50μm were fabricated, respectively, by stirring casting and direct squeeze casting process under 100MPa. The effects of particle size on microstructures and mechanical properties of the composites were investigated.The results reveal that with the increases of particle size, the porosity in the composites prepared is decreased gradually with more uniform distribution, and tensile strength, yield strength, elongation and hardness of the 10SiC_p/6061 composites are decreased, meanwhile, the fracture mechanism of the composites prepared is transformed from ductile fracture to ductile-brittle mixed fracture.

The alloy slurry was prepared by ultrasound vibration thermal equilibrium method, direct thermal equilibrium method and traditional casting process.Then die-casting forming was conducted at the same pouring temperature, mold temperature, injection pressure and injection speed.The heart part and edge part of die castings were sampled, and the microstructure was observed.The same part of die castings was sampled for tension test.The effects of different process conditions on microstructure and mechanical properties of die castings were analyzed comparatively.The results show that the microstructure of die castings obtained by ultrasound vibration thermal equilibrium method semi-solid process presents the most tiny, round and uniform structure with the satisfied mechanical properties, and then that by direct thermal equilibrium method.After T6 treatment, the comprehensive mechanical properties of die castings are improved significantly.

The diamond/Cu composites were fabricated by spark plasma sintering (SPS).The effects of diamond particles on the relative density, thermal conductivity, tensile strength and elongation of the composites were analyzed.The results show that with the increase of diamond content, the relative density, thermal conductivity, tensile strength and elongation of the diamond/copper composites are increased firstly and then decreased.With the diamond content of 1.0%, the tensile strength of the composite can reach the maximum value of 221.35MPa.The maximum density can be obtained with the diamond content of 1.5%, and the thermal conductivity and elongation reach the maximum value when the diamond content is 2.0%.The fractures of diamond/copper matrix composites are characterized by ductile fracture and interfacial debonding.

3D printing titanium alloy is suitable for manufacturing complex shape components, which can reduce production process and improve material utilization. In recent years, the application of 3D printing additive manufacturing technology in the production of titanium alloy components achieves rapid development and significant advantages in order to obtain the more complex structure of titanium alloy components, and further reduce the cost and shorten the production cycle. The application advantages, characteristics of classification and process, status and development direction of 3D printing technology in titanium alloy casting production were systematically introduced.

Three generation single crystal superalloys(SRR99,DD32 and DD90)were designed by the combination of directional solidification technology and seeding method.The primary dendrite spacings were calculated by the direct measurement method and the square calculation method.The effects of grain boundary and crystallographic orientation on the primary dendrite spacing were eliminated.The average primary dendrite spacings of three superalloys are increased gradually with the increase of solidification heights,and the ones counted by two methods are similar,confirming the accuracy of the two methods.Moreover,the primary dendrite spacings of the superalloys is varied in a large range and present a normal distribution.The upper limit of the primary dendrite spacing is 5.4~8.5 times higher than the lower limit.

The electromagnetic field, flow field and thermal field of 7075 aluminum alloy during melt treatment in spiral annular electromagnetic field were simulated by the commercial numerical software Ansys Workbench.Numerical results show that compared with rotating electromagnetic field, the 7075 alloy melt is stirred forcely by a spiral electromagnetic field both in radial and axial directions.The temperature gradient of the 7075 alloy melt is narrawed.Subsequently, the numerical results were verified experimentally, and the experimental results were consistent with the numerical ones.The average grain size of 7075 alloy treated by spiral annular electromagnetic field is reduced, and the uniformity is improved obviously.The macro-segregation of the 7075 alloy casting is decreased obviously.

The action mechanism of oxide layer crack and volatilization of molybdenum oxides in the oxidative kinetics of high entropy alloy Mo₂₅Nb₂₅Ta₂₅W₂₅ was described.An equal mole ratio Mo₂₅Nb₂₅Ta₂₅W₂₅ alloy with a simple BCC structure was prepared by hot-pressing sintering.The oxidation behavior of the high entorpy alloy were analyzed at 800℃、900℃ and 1 000℃, respectively, and the oxidation mechanism was expounded.The oxides were characterized by XRD, SEM and electron probe X-ray microanalyzer (EPMA).The results reveal that at oxidation temperature range, the main oxidation products are Ta₁₆W₁₈O₉₄ and Nb₁₄W₃O₄₇ with some protection in the oxide layer.The kinetics of the tested samples follows the parabolic law at 800℃, while follows the linear law at the middle of 900℃ and 1 000℃, which are attributed to the volatilization of MoO₃ leading to oxide layer loose and porous at higher temperature.

Hot compressive characteristics of 6061 aluminum alloy were investigated on Gleeble-3500 thermal simulation machine by performing isothermal compression tests at 300~450℃ and 0.0110s^-1 with the maximum reduction of 60%.The flow stress behavior of 6061 aluminum alloy at high-temperature was analyzed and the hot processing map was established based on the dynamic material model(DMM).Moreover,the hot deformation mechanism was described according to the associated microstructure observation.The results show that the flow stress is decreased by increasing in the deformation temperature and decreasing in the strain rate,and the main softening mechanism of 6061 aluminum alloy is characterized by dynamic recovery.The instability zones of flow behavior appear widely at higher strain rate on the processing map.The optimum process interval of 6061 aluminum alloy for hot working is the deformation temperature at 430~450℃ and strain rate of 0.010.05s^-1,in which some recrystallized grains canbe observed.

Automobile wheel hub industry is a rising industry of automobile parts in China,and the amount of patents are increased rapidly.Two leading enterprises:CITIC Dicastal and Lizhong Wheel Group were selected by using Patsnap patents analysis tool and FMEA to analyze comparatively technological direction and innovation strategy from patent application,technical distribution,key patents,innovation strategy and patent value.Some suggestions were presented in order to provide reference for innovation development of China's automobile wheel hub industry.

The effects of tool rotation speed on microstructure and corrosion behavior of friction stir welding seam were investigated for 6063 aluminum alloy.The corrosion behavior of the base materials and friction stir welding seams were tested in 3.5% (mass fraction) aqueous NaCl solution by static weightloss test, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).Meanwhile, their microstructure and corrosion morphology were observed by the optical microscope (OM) and scanning electron microscope (SEM).The results show that welding joints formed by friction stir welding consists of three regions:a base material zone (BMZ), a thermo-mechanically affected zone (TANZ) and a weld nugget (WN).The grains are transformed from coarse block grains in the material zone to fine equiaxed grains in the weld nugget, and a significant plastic flow phenomenon is observed in the thermo-mechanically affected zone, respectively.The results obtained from the static weightloss test suggest that the average corrosion rate of base material and welding seam are 0.078 1、0.231 5、0.347 2 and 0.405 1g/(m²·h), respectively.Electrochemical tests show that the corrosion potential of welding seam is more negative than that of basic material, and the corrosion density presents the higher, meanwhile, the oxide resistance and polarization resistance are lower, compared with those of the parent alloy, which indicates that the friction stir welding seam exhibits lower corrosion resistance than the basic material.With increasing in the tool rotation speed, the corrosion resistance of the welding seam is gradually reduced.The pitting and intergranular are main corrosion mechanisms in the corroded areas within the welding seam and basic material of 6063 aluminum alloy.The refinement of grains and increase of grain boundary are responsible for the lower corrosion resistance of the welding seam during friction stir welding.

According to its structure,the die casting process of aluminum alloy heat sink was designed, and then simulated by Flow-3D software.The results reveal that gas-entrapped defects can be observed in its four edges of part bottom.Crack detection and sectioning observation on the test-piece of the trialproduction show that the simulated results are well consistent with practical observation,where many blowholes and pinholes can be observed in the edge parts.Process optimization was carried out to adjust the size of ingate.Its results show that the defects can be eliminated effectively.Based on the optimized process,the samples were produced.The results are well in agreement with the simulated ones,where blowholes and pinholes are eliminated greatly,meeting application requirements and reducing the defective rate.