A computer control system for automatic TIG welding of aluminium alloy sheets

Aimed at the welding ttechnological requirements of foe missile shell,a computer control system for automatic TIG welding of aluminium alloy sheets has been developed in this paper.The hardware of the system is composed of the four sub-systems,i.e.weldingpower source,arc length controller,welding wire feeder and welding head traveller.The software of the system comprises the on-line executing program and the off-line serving program.The operating principle,specifications and control of the system are introduced.The experiments indicate that the system possesses rational hardware structure and practical software function,and has solved the problem of high frequency interference to the computer control system. Therefore,the control system can satisfy the requirements of automatic TIG welding of the missile shell.

A Comparison of Laser Cladding Ni-based Coating on an Aluminium Alloy with CO_2 Laser and Nd: YAG Laser

In this paper, a plasma sprayed coating (Ni Cr B Si) on an Al Si alloy surface was melted by a CO 2 laser and a Nd:YAG laser respectively. The difference on the outline of the melted zone, chemical composition and hardness distribution of the laser melted zones were investigated. Experimental results showed that samples treated by the Nd:YAG laser have a better cladding tendency, more uniform chemical composition and microhardness distribution. Samples treated by the CO 2 laser have larger compositional segregation and poorer microhardness distribution.

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.

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.

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.

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.

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.

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.

Modified constitutive model and workability of 7055 aluminium alloy in hot plastic compression

To obtain flow behavior and workability of 7055 aluminium alloy during hot deformation,hot compression tests at different temperatures and strain rates are conducted.True stress?strain curves of 7055 aluminium alloy under different conditions are obtained and the flow stress increases with ascending strain rate and descending temperature.For Arrhenius constitutive equation,each material parameter is set as a constant,which will bring forth large error for predicting flow behavior.In this work,material parameters are fitted as a function of temperature or strain rate based on experimental results and a modified constitutive equation is established for more accurate prediction of flow behavior of 7055 aluminium alloy.The effects of temperature and strain rate on power dissipation and instability are analyzed to establish a processing map of 7055 aluminium alloy.The dominant deformation mechanism for microstructure evolution at different deformation conditions can be determined and high efficiency of power dissipation may be achieved from power dissipation map.Meanwhile,proper processing parameters to avoid flow instability can be easily acquired in instability map.According to the processing map,optimized processing parameters of 7055 aluminium alloy are temperature of 673?723 K and strain rate of 0.01?0.4 s^?1,during which its efficiency of power dissipation is over 30%.Finite element method(FEM)is used to obtain optimized parameter in hot rolling process on the basis of processing map.

Effect of welding processes on AA2219 aluminium alloy joint properties

AA2219 aluminium alloy square butt joints without filler metal addition were fabricated using gas tungsten arc welding （GTAW）, electron beam welding （EBW） and friction stir welding （FSW） processes. The effects of three welding processes on the tensile, fatigue and corrosion behaviour were studied. Microstructure analysis was carried out using optical and electron microscopes. The results show that the FSW joints exhibit superior tensile and fatigue properties compared to EBW and GTAW joints. It is also found that the friction stir welds show lower corrosion resistance than EB and GTA welds. This is mainly due to the presence of finer grains and uniform distribution of strengthening precipitates in the weld metal of FSW joints.

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.

Prediction and optimization of friction welding parameters for joining aluminium alloy and stainless steel

Friction welding （FW） is a process of solid state joining which is used extensively in recent years due to its advantages such as low heat input,production efficiency,ease of manufacture and environment friendliness.Friction welding can be used to join different types of ferrous metals and non-ferrous metals that cannot be welded by traditional fusion welding processes.The process parameters such as friction pressure,forging force,friction time and forging time play the major roles in determining the strength of the joints.In this investigation an attempt was made to develop an empirical relationship to predict the tensile strength of friction welded AA 6082 aluminium alloy and AISI 304 austenitic stainless steels joints,incorporating above said parameters.Response surface methodology （RSM） was applied to optimizing the friction welding process parameters to attain the maximum tensile strength of the joint.

Fatigue life prediction of aviation aluminium alloy based on quantitative pre-corrosion damage analysis

A new method of quantitative pre-corrosion damage of aviation aluminium(Al-Cu-Mg)alloy was proposed,whichregarded corrosion pits as equivalent semi-elliptical surface cracks.An analytical model was formulated to describe the entire regionof fatigue crack propagation(FCP).The relationship between the model parameters and the fatigue testing data obtained in thepre-corroded experiments,crack propagation experiments and S-N fatigue experiments was discussed.The equivalent crack sizesand the FCP equation were used to calculate the fatigue life through numerical integration based on MATLAB/GUI.The resultsconfirm that the sigmoidal curve fitted by the FCP model expresses the whole change from Region I to Region III.In addition,thepredicted curves indicate the actual trend of fatigue life and the conservative result of fatigue limit.Thus,the new analytical methodcan estimate the residual life of pre-corroded Al-Cu-Mg alloy,especially smooth specimens.

Geometrical, microstructural and mechanical characterization of pulse laser welded thin sheet 5052-H32 aluminium alloy for aerospace applications

Pulse laser welding of 0.6 mm-thick AA5052-H32 was performed to determine the optimum set of parameters including laser pulse current,pulse frequency and pulse duration that meets the AWS D17.1 specifications for aerospace industry.The microstructure and mechanical properties of the weldments were also investigated.Relationships between the parameters and weld bead geometry were found.High quality weld joints without solidification crack that met AWS D17.1 requirements were obtained at(I)high pulse energy(25 J)and high average peak power(4.2 kW)and(II)low pulse energy(17.6 J)and low average peak power(2.8 kW).The weld joint formed at lower heat energy input exhibited finer dendritic grain structure.Mg vapourisation and hard phase compound(Al0.5Fe3Si0.5)formation decreased in the weld joint formed at lower heat energy input.Consequently,the tensile strength of the weldment formed at lower heat energy input(168 MPa)is by a factor of 1.15 higher but showed^29%decrease in hardness(111 HV0.1)at the joint when being compared with the weldment formed at higher heat energy input.Appropriate parameters selection is critical to obtaining 0.6 mm-thick AA5052-H32 pulse laser weld joints that meet AWS D17.1 requirements for aircraft structures.

Electrochemical corrosion behaviour of stir zone of friction stir welded dissimilar joints of AA6061 aluminium-AZ31B magnesium alloys

Joining of dissimilar metals will offer many advantages in transportation sectors such as fuel consumption,weightreduction and emission reduction.However,joining of aluminium(Al)alloys with magnesium(Mg)alloys by fusion welding processis very complicated.Friction stir welding(FSW)is a feasible method to join these two dissimilar alloys.Mixing these two metalstogether in stir zone(SZ)leads to poor corrosion resistance.In this investigation,an attempt has been made to understand thecorrosion resistance of SZ of FSWed dissimilar joints of AA6061Al alloy and AZ31B Mg alloy.Potentiodynamic polarization testwas conducted by varying chloride ion concentration,pH value of the NaCl solution and exposure time.The corroded surfaces wereanalyzed using optical microscopy,scanning electron microscopy and XRD techniques.Of these three factors investigated,exposuretime is found to be the most significant factor to influence the corrosion behaviour of SZ of friction stir welded dissimilar joints ofAl/Mg alloys.