Effectiveness of Sodium Silicate on the Corrosion Protection of AA7075-T6 Aluminium Alloy in Sodium Chloride Solution

The influence of sodium silicate on the corrosion behaviour of aluminium alloy 7075-T6 in 0.1 M sodium chloride solution was studied by open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) techniques. Scanning electron microscopy (SEM) was used to characterize the AA7075-T6 surface. Silicate can significantly reduce corrosion deterioration and the inhibition efficiency increases with the concentration of Na2SiO3. The corrosion inhibition mechanism involves the formation of a protective film over the alloy surface by adsorption of aluminosilicate anions from solution, as has also been suggested by others in literature.

Influence of introducing Zr,Ti,Nb and Ce elements on externally solidified crystals and mechanical properties of high-pressure die-casting Al–Si alloy

High pressure die casting(HPDC)AlSi10Mn Mg alloy castings are widely used in the automobile industry.Mg can optimize the mechanical properties of castings through heat treatment,while the release of thermal stress arouses the deformation of large integrated die-castings.Herein,the development of non-heat treatment Al alloys is becoming the hot topic.In addition,HPDC contains externally solidified crystals(ESCs),which are detrimental to the mechanical properties of castings.To achieve high strength and toughness of non-heat treatment die-casting Al-Si alloy,we used AlSi9Mn alloy as matrix with the introduction of Zr,Ti,Nb,and Ce.Their influences on ESCs and mechanical properties were systematically investigated through three-dimensional reconstruction and thermodynamic simulation.Our results reveal that the addition of Ti increased ESCs'size and porosity,while the introduction of Nb refined ESCs and decreased porosity.Meanwhile,large-sized Al_3(Zr,Ti)phases formed and degraded the mechanical properties.Subsequent introduction of Ce resulted in the poisoning effect and reduced mechanical properties.

Microstructure and mechanical properties of ceramic coatings formed on 6063 aluminium alloy by micro-arc oxidation

The microstructure and mechanical properties of ceramic coatings formed on 6063 aluminium alloy obtained in silicate-,borate- and aluminate-based electrolyte without and with nanoadditive Al2O3 and TiO2 by micro-arc oxidation（MAO） were studied by scanning electron microscopy（SEM）,energy-dispersive X-ray spectroscopy（EDS）,X-ray diffraction（XRD）,microhardness and friction-abrasion tests,respectively.SEM results show that coatings with nanoadditive have less porosities than those without nanoadditive.XRD results reveal that nanoadditive-containing coatings contain more oxides compared with nanoadditive-free coatings in all cases,which are consistent with the EDS analysis.Mechanical properties tests show that nanoadditive Al2O3-containing coatings have higher microhardness values compared with the other coatings obtained in silicate-,borate- and aluminate-based electrolyte.On the other hand,nanoadditive has a positive effect on improving the wearing-resistance of MAO coatings in all cases.Furthermore,the borate-MAO coatings present an inferior anti-wearing property compared with the silicate- and aluminate-MAO coatings for both the nanoadditive-free and nanoadditive-containing coatings.

Shear deformation and plate shape control of hot-rolled aluminium alloy thick plate prepared by asymmetric rolling process

Asymmetric rolling （ASR）, as one of severe plastic deformation （SPD） methods to make ultra-fine materials with enhanced performance is mainly used to prepare foil and thin strip. The asymmetrical rolling was achieved by adjusting the diameters of the upper roll and the bottom roll and was used to prepare hot-rolled thick plate of 5182 aluminium alloy. The shear deformation and plate shape control were experimentally studied. The experimental results show that asymmetrical rolling has a significant effect on metal deformation stream and can somehow refine microstructure and improve the uniformity of microstructure and properties. The asymmetrical rolling process can also reduce the rolling force. However, bending of rolling plate often happens during asymmetrical rolling process. The factors affecting the bending were discussed.

Visualization and simulation of plastic material flow in friction stir welding of 2024 aluminium alloy plates

Thin copper sheets as marker material were embedded into weld path of 2024 aluminium alloy plates and their final position after friction stir welding was examined by metallographic techniques. Referring to the visualized material flow patterns, a three-dimensional model was developed to conduct the numerical simulation of the temperature profile and plastic material flow in friction stir welding. The calculated velocity contour of plastic flow in close proximity of the tool is generally consistent with the visualized results. As the tool rotation speed increases at a constant tool travel speed, the material flow near the pin gets stronger. The predicted shape and size of the weld nugget zone match with the experimentally measured ones.

Fatigue behavior and life prediction of A7N01 aluminium alloy welded joint

Fatigue characteristics of A7N01 aluminium alloy welded joint were investigated and a fatigue crack initiation life-based model was proposed. The difference of fatigue crack initiation life among base metal, weld metal and heat affected zone (HAZ) is slight. Furthermore, the ratio of fatigue crack initiation life (Ni) to fatigue life to failure(Nf) is a material dependent parameter, 26.32%, 40.21% and 60.67% for base metal, HAZ and weld metal, respectively. Total fatigue life predicted using the presented model is in good agreement with the experimental data and that using Basquin’s model. The observation results of fatigue fracture surfaces, using scanning electron microscope (SEM), demonstrate that fatigue crack initiates from smooth surface due to welding process for weld metal, blowhole in HAZ causes fatigue crack initiation, and the crushed second phase particles play an important part in fatigue crack initiation in base metal.

Effect of pre-stretching on microstructure of aged 2524 aluminium alloy

The effects of pre-stretching following solution treatment on the hardness and microstructures of aged 2524 aluminium alloy at 170 ℃ were studied.Ageing hardness values under different pre-stretching conditions were measured,and the corresponding microstructures were characterized by transmission electron microscopy（TEM）.The results show that compared with unstretched samples,the peak hardness is increased and the time to reach the peak hardness is reduced with the increase of pre-strain;the number density of S（Al2CuMg） phases is increased and the length is shortened in pre-stretched alloy.Additionally,the number density of GPB zones is decreased with the increase of pre-strain in peak-aged samples.When the pre-strain is up to 5%,S phases play the predominant contribution to the peak hardness.Fine and uniformly distributed S phases lead to a higher hardness than GPB zones together with S phases existing in conventionally aged 2524 alloy.

Effect of electromagnetic field on microstructure and macrosegregation of flat ingot of 2524 aluminium alloy

Low frequency electromagnetic casting （LFEC） process with the application of an induction coil outside the conventional direct chill （DC） casting mould was used to prepare the flat ingot of 2524 alloy and the effect of electromagnetic field on the microstructure and macrosegregation of this alloy was systematically studied. The results show that the fiat ingot prepared by the LFEC process has a finer and more uniform as-cast microstructure and the grain morphology is transformed from dendrite and rosette-like to equiaxed structure. The LFEC process also shows a significant effect on macrosegregation, and with the application of electromagnetic field during casting process, the segregation in the centre of the ingot is obviously reduced. The mechanism of these effects was also discussed.

Microstructural effects in corrosion of aluminium tube alloys

Fine gauge extruded aluminium alloy tubes can experience preferential corrosion and early failure when they are formed into ＂u-bend＂ via cold deformation. The relationship between the electrochemical reactivity and the microstructure of the bent vs straight parts of the tube was established. Investigations were carried out on two alloys containing 0.08% and 0.22% （mass fraction） of manganese. The corrosion morphology of bent tubes after immersion in salt water acetic acid test （SWAAT） solution showed the highest attack at the bent region of the high-Mn alloy. SEM characterisation of the alloys showed that each alloy has one main type of coarse intermetallic particle. However, TEM observation showed that there is a distinct difference in particle morphology between the bent and straight regions of the high-Mn tubes, the bent region revealed an additional population of 10 50 nm Mn-rich intermetallic particles, which increased both the anodic and cathodic reactivity. For the low-Mn alloy, no such effects were observed. The results suggested that cold deformation of the high-Mn tube allowed room temperature precipitation of fine Mn-rich particles, which increased the cathodic reactivity of that region by providing more cathodic sites, and increased the susceptibility to pitting by removing noble Mn from solid solution. Such an effect was not observed for the low-Mn alloy.

Effect of post weld heat treatment on properties of variable polarity TIG welded AA2219 aluminium alloy joints

AA2219 aluminium alloy joints were fabricated by variable polarity tungsten inert gas （VPTIG） welding process and the effects of post weld heat treatment （PWHT） on the tensile properties, microstructure and fatigue behaviour of the welded joints were investigated. The VPTIG welding process was adopted because it could meet the need of cathode cleaning and meanwhile it could reduce the deterioration of tungsten electrode furthest. The welded samples were divided into as-welded （AW） sample and PWHT sample. The PWHT method used on the samples was solution treatment （535 ℃, 30 rain）, water quenching and artificial aging （175 ℃, 12 h）. The experimental results show that, compared with the AW samples, the microstructure characteristics and mechanical properties of the AA2219 joints after PWHT were significantly improved. The improvement of yield strength, ultimate tensile strength, and fatigue strength are 42.6%, 43.1% and 18.4%, respectively.

Prediction of flow stress of 7017 aluminium alloy under high strain rate compression at elevated temperatures

An artificial neural network(ANN) constitutive model and JohnsoneC ook(Je C) model were developed for 7017 aluminium alloy based on high strain rate data generated from split Hopkinson pressure bar(SHPB) experiments at various temperatures. A neural network configuration consists of both training and validation, which is effectively employed to predict flow stress. Temperature, strain rate and strain are considered as inputs, whereas flow stress is taken as output of the neural network. A comparative study on Johnsone Cook(Je C) model and neural network model was performed. It was observed that the developed neural network model could predict flow stress under various strain rates and temperatures. The experimental stressestrain data obtained from high strain rate compression tests using SHPB over a range of temperatures(25 e300 C), strains(0.05e0.3) and strain rates(1500e4500 s 1) were employed to formulate JeC model to predict the flow stress behaviour of 7017 aluminium alloy under high strain rate loading. The JeC model and the back-propagation ANN model were developed to predict the flow stress of 7017 aluminium alloy under high strain rates, and their predictability was evaluated in terms of correlation coefficient(R) and average absolute relative error(AARE). R and AARE for the J-C model are found to be 0.8461 and 10.624%, respectively, while R and AARE for the ANN model are 0.9995 and 2.58%, respectively. The predictions of ANN model are observed to be in consistent with the experimental data for all strain rates and temperatures.

Electrodeposition of aluminium and aluminium-copper alloys from a room temperature ionic liquid electrolyte containing aluminium chloride and triethylamine hydrochloride

The electrodeposition of A1 and A1-Cu binary alloys on to gold substrates from a room temperature ionic liquid electrolyte containing A1C13-EtaNHC1 was studied. The electrochemical behavior of the electrolyte and the mechanism of deposition were investigated through cyclic voltammetry （CV）, and the properties of deposits obtained were assessed by scanning electron microscopy with energy dispersive X-ray spectroscopy （SEM-EDS） and X-ray diffraction （XRD）. A1 of 70μm in thickness and an A1-Cu alloy of 30μm in thickness with 8at% copper were deposited from the electrolyte. SEM images of the deposits indicate that the A1 deposit was smooth and uniform, whereas the Al-Cu deposit was nodular. The average crystalline size, as determined by XRD patterns, was found to be （30±5） and （29±5） nm, respectively, for A1 and A1-Cu alloys. Potentiodynamic polarization （Tafel plots） and electrochemical impedance spectroscopic （EIS） measurements showed that Al-Cu alloys are more corrosion resistant than Al.

CORROSION BEHAVIOR OF A ZIRCONIUM-TITANIUM BASED PHOSPHONIC ACID CONVERSION COATING ON AA6061 ALUMINIUM ALLOY

The conversion coating was formed by dipping AA6061 in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid （ATMP） solution at room temperature. The formation process and the anti-corrosion performance of the conversion coating were investigated using electrochemical test and salt spray test （SST）, respectively. The electrochemical test shows that the Zr/Ti and ATMP coating improves the corrosion resistance of AA6061 as good as the chromate （VI） coating. But the results of SST show that the corrosion resistance of Zr/Ti and ATMP coating is not as good as the chromate （VI） coating. The corrosion area is less than 2% after 72 h.

Heat treatment of 7xxx series aluminium alloys—Some recent developments

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.

Enhancement of wear and ballistic resistance of armour grade AA7075 aluminium alloy using friction stir processing

Industrial applications of aluminium and its alloys are restricted because of their poor tribological properties. Thermal spraying, laser surfacing, electron beam welding are the most widely used techniques to alter the surface morphology of base metal. Preliminary studies reveal that the coating and layering of aluminium alloys with ceramic particles enhance the ballistic resistance. Furthermore, among aluminium alloys,7075 aluminium alloy exhibits high strength which can be compared to that of steels and has profound applications in the designing of lightweight fortification structures and integrated protection systems. Having limitations such as poor bond integrity, formation of detrimental phases and interfacial reaction between reinforcement and substrate using fusion route to deposit hard particles paves the way to adopt friction stir processing for fabricating surface composites using different sizes of boron carbide particles as reinforcement on armour grade 7075 aluminium alloy as matrix in the present investigation. Wear and ballistic tests were carried out to assess the performance of friction stir processed AA7075 alloy. Significant improvement in wear resistance of friction stir processed surface composites is attributed to the change in wear mechanism from abrasion to adhesion. It has also been observed that the surface metal matrix composites have shown better ballistic resistance compared to the substrate AA7075 alloy. Addition of solid lubricant Mo S2 has reduced the depth of penetration of the projectile to half that of base metal AA7075 alloy. For the first time, the friction stir processing technique was successfully used to improve the wear and ballistic resistances of armour grade high strength AA7075 alloy.

DEFORMATION BEHAVIOR OF AA6063 ALUMINIUM ALLOY AFTER REMOVING FRICTION EFFECT UNDER HOT WORKING CONDITIONS

The hot deformation behavior of AA6063 aluminium alloy has been investigated by means of compression tests at temperatures between 400 and 520℃, and strain rates ranging from 2.5 to 10 s^-1. Owing to the barreling, the theoretical model on the basis of Hills general method is used to calculate the flow stress of a cylindrical specimen under uniaxial simple compression so as to consider the friction effect at the die-specimen interface. A method of evaluating the friction coefficient by combining compression tests with the finite element method is presented. The real flow behavior of AA6063 aluminium alloy can be described with sinh-Arrhenius equation. The hot deformation activation energy Q derived from the corrected stress and strain data is 232. 350 kJ/mol.

Optimizing the micro-arc oxidation (MAO) parameters to attain coatings with minimum porosity and maximum hardness on the friction stir welded AA6061 aluminium alloy welds

Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relationships were derived to evaluate the MAO coating properties(porosity and hardness) by incorporating very important MAO parameters(current density, inter-electrode distance and oxidation time). MAO parameters were also optimized to achieve coatings with minimum porosity and maximum hardness. Further, the effect of MAO parameters on coating characteristics was analysed. From the results, it is found that the current density has greater influence on the responses than the other two parameters.

Experimental and numerical investigation on under-water friction stir welding of armour grade AA2519-T87 aluminium alloy

Friction stir welding(FSW) is a promising welding process that can join age hardenable aluminium alloys with high joint efficiency. However,the thermal cycles experienced by the material to be joined during FSW resulted in the deterioration of mechanical properties due to the coarsening and dissolution of strengthening precipitates in the thermo-mechanical affected zone(TMAZ) and heat affected zone(HAZ). Under water friction stir welding(UWFSW) is a variant of FSW process which can maintain low heat input as well as constant heat input along the weld line. The heat conduction and dissipation during UWFSW controls the width of TMAZ and HAZ and also improves the joint properties. In this investigation, an attempt has been made to evaluate the mechanical properties and microstructural characteristics of AA2519-T87 aluminium alloy joints made by FSW and UWFSW processes. Finite element analysis has been used to estimate the temperature distribution and width of TMAZ region in both the joints and the results have been compared with experimental results and subsequently correlated with mechanical properties.? 2016 China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.

Effect of fusion welding processes on tensile properties of armor grade, high thickness, non-heat treatable aluminium alloy joints

AA5059 is one of the high strength armor grade aluminium alloy that finds its applications in the military vehicles due to the higher resistance against the armor piercing (AP) threats. This study aimed at finding the best suitable process among the fusion welding processes such as gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) by evaluating the tensile properties of AA5059 aluminium alloy joints. The fracture path was identified by mapping the low hardness distribution profile (LHDP) across the weld cross section under tensile loading. Optical and scanning electron microscopies were used to characterize the microstructural features of the welded joints at various zones. It is evident from the results that GTAW joints showed superior tensile properties compared to GMAW joints and this is primarily owing to the presence of finer grains in the weld metal zone (WMZ) and narrow heat-affected zone (HAZ). The lower heat input associated with the GTAW process effectively reduced the size of the WMZ and HAZ compared to GMAW process. Lower heat input of GTAW process results in faster cooling rate which hinders the grain growth and reduces the evaporation of magnesium in weld metal compared to GMAW joints. The fracture surface of GTAW joint consists of more dimples than GMAW joints which is an indication that the GTAW joint possess improved ductility than GMAW joint.

RAPID NONDESTRUCTIVE TESTING OF HEAT-TREATMENT QUALITY OF 2014 ALUMINIUM ALLOY

１ＩＮＴＲＯＤＵＣＴＩＯＮＳｉｎｃｅｔｈｅｐａｐｅｒ“Ｒａｐｉｄ，ＮｏｎｄｅｓｔｒｕｃｔｉｖｅＡｎｄＱｕａｎｔｉｔａｔｉｖｅＴｅｓｔｉｎｇｏｆＨａｒｄｎｅｓｏｆＡｌｕｍｉｎｉｕｍａｌｏｙｓ”ｗａｓｐｕｂｌｉｓｈｅｄ［１］，ｍａｎｙｒｅａｄｅｒｓｈａ...