Mg In Alloy Research Articles

Effect of Mg addition on strengthening of aluminium alloys subjected to different strain paths in high pressure torsion

The effect of Mg addition on strengthening of aluminium alloys was studied by monotonic, cyclic and single reversal deformation in high pressure torsion. The results show the extent of strengthening varies between these three processing methods and are dependent on Mg content. There is a relatively low hardness increment in commercially pure aluminium, slightly higher hardness increment in an Al–1Mg alloy and significant hardness increment in an Al–2Mg alloy. The difference of strengthening due to strain paths is discussed in terms of geometrically necessary dislocations.

Electro-pulse modification and reheating process for production of thixotropic microstructure in AlSi 7Mg alloy

Electro-pulse modification (EPM) was used to change the dendritic structure of AlSi 7Mg alloy to globular one. The effects of the modified temperature, electro-pulse frequency and time on the solidified structure were examined. The results show that these parameters play an important role in the solidified microstructures. That is to say, under the same modified temperature, the solidified microstructure will be improved greatly with the increase of electro-pulse frequency and time, but when they exceed to limit values, the solidified microstructure will become worse, resulting from the decrease of the ratio of nucleation. The experimental results indicate that the suitable modified temperature of AlSi 7Mg alloy is 720 °C, and the appropriate electro-pulse frequency and time are 5 Hz and 40 s, respectively. Then the microstructures produced by suitable EPM process were reheated at temperatures between liquidus and solidus, the primary-Al grains ripen further and become more spherical, which is favorable to the semi-solid forming of AlSi 7Mg alloy.

X-ray photoelectron spectroscopy investigations of zinc–magnesium alloy coated steel

The coating layer composition depth profiles and element chemical states of zinc–magnesium alloy coated steel were investigated by X-ray photoelectron spectroscopy depth profiling. Through the analysis of photoelectron signals and Auger signals of different elements on different depth planes of the coating layer, it can be found that the surface of the coating layer contains MgCO 3, MgO, Mg(OH) 2, metallic Mg, metallic Zn and some complex zinc compounds. Under the surface, there is a Zn 2Mg alloy layer with the thickness of about 300 nm accompanied with MgO and Mg(OH) 2 in the layer. There is a transitional layer with the thickness of about 200 nm between the Zn 2Mg alloy layer and the pure Zn layer, whose components consist of zinc–magnesium alloy without fixed stoichiometry, a little MgO and a little Mg(OH) 2.

Modeling the TDFD dissolution of Al–Fe–Mn–Si particles in an Al–4.5Zn–1Mg alloy

Dissolution of large particles in DC-cast 7xxx aluminum alloys is one of the primary objectives of the homogenization process. A mathematical model to describe and predict this complex thermodynamical and kinetical process is of great significance. In this paper, the details of a diffusion-limited dissolution model, based on the thinning, discontinuation and full dissolution (TDFD) mechanism, to predict the dissolution of the Al17(Fe3.2, Mn0.8)Si2 particles is described. The model is capable of predicting the volume fraction and thickness of the particles during homogenization at different temperatures and time intervals. The predicted results are in good agreement with measurements using quantitative X-ray diffraction (QXRD) and quantitative field emission gun-scanning electron microscopy (QSEM). The model predictions of the supersaturation parameter, interface position, interface movement rate of the planar surfaces and the cylindrical edges, and the effect of the occurrence of discontinuities on the dissolution extent are presented.

Response of materials as a function of grinding angle on friction and transfer layer formation

Surface texture influences friction and transfer layer formation during sliding contact. In the present investigation, basic studies were conducted using an inclined pin-on-plate sliding apparatus to understand the effect of grinding mark directionality on the coefficient of friction and transfer layer formation. In the experiments, 080 M40 steel plates were ground to attain different surface roughness with unidirectional grinding marks. Pins consisting of soft materials (pure Al, pure Mg, and Al–4Mg alloy) were then slid against the prepared steel plates. The grinding angle (angle between direction of sliding and grinding marks) was varied between 0° and 90° in the tests. The experiments were conducted under both dry and lubricated conditions in an ambient environment. It was observed that the transfer layer formation and the coefficient of friction depend primarily on the directionality of the plate grinding marks. For the case of pure Mg pins, a stick-slip friction phenomenon was observed for all grinding angles under dry conditions and for grinding angles over 25° under lubricated conditions. In the case of Al pins, the stick-slip phenomenon was observed only under lubricated conditions for angles exceeding 25°. The stick-slip phenomena did not occur in any of the conditions studied with Al–4Mg alloy pins. Based on the results, it was concluded that the magnitudes of the friction and the stick-slip motion amplitude (for Al and Mg pins) were primarily controlled by changes in the level of plowing friction.

Thermally formed oxide films on Al–6Zn–XMg (X = 0 and 2 mass%) alloys heated in different gases

In this study, thermogravimetric analysis (TG) testing is used to measure the mass loss of polished Al–6Zn–XMg (X = 0 and 2 mass%) alloy samples heated at 773 K for 6 h in dry air or nitrogen gas. The progressive development of thermally formed oxides on an Al–6Zn–XMg (X = 0 and 2 mass%) alloy as shown by X-ray diffractometer analyses is discussed. Zn-spinel and Mg-spinel are detected on the Al–6Zn and Al–6Zn–2Mg alloy samples, respectively, and then heated in the dry air atmosphere; AlN and Mg3N2 are detected in alloy samples heated in nitrogen gas. The chain reactions that cause the serrated change in the mass loss curve are proposed and discussed.

On nucleation and propagation of PLC bands in an Al–3Mg alloy

The processes of nucleation and propagation of Portevin–LeChatelier deformation bands during tensile deformation of the alloy AA5754 have been investigated by a special optical technique for local strain measurements, combining both a line-scan and a CMOS camera to record the changes of surface strain, applying digital image correlation. Examples for bands of types A and B are observed and discussed with respect to the micro-mechanisms of their nucleation and propagation, emphasizing local stress concentrations in addition to the well-known effects of dynamic strain aging and dislocation interactions for explaining the PLC behavior. Finally the nucleation and propagation of PLC bands are simulated by computations based on a simple constitutive model.

Dry sliding wear behaviour of Al–12Si–4Mg alloy with cerium addition

The purpose of this work is to understand the effect of cerium addition on wear resistance behaviour of as-cast alloys. Al–12Si–4 Mg alloys with 1–5 wt% cerium addition were prepared using the casting technique. A sliding wear test was carried out under applied loads of 10 N, 30 N and 50 N at a fixed sliding speed of 1 m/s using a pin-on-disc configuration. The wear test was conducted in dry conditions at room temperature of ∼25 °C. Detailed analysis of the microstructure, worn surface, collected debris and microhardness was undertaken in order to investigate the differences between the as-cast alloys with different levels of cerium addition. The addition of 1–5 wt% cerium was found to lead to the precipitation of intermetallic phases (Al–Ce), resulting a needle-like structures. Increasing cerium content up to 2 wt% improved both wear resistance and microhardness of as-cast alloys. Addition of more than 2 wt% cerium, however, led to a decrease in microhardness, resulting in lower wear resistance of the alloys. Moderate wear was observed at all loads, with specific wear rates ( K′) ranging from 6.82 × 10 −5 with 2 wt% Ce at applied load of 50 N to 21.48 × 10 −5 mm 3/N m without added Ce at an applied load of 10 N. Based on K′ ranges, the as-cast alloys exhibited moderate wear regimes, and the mechanism of wear is a combination of abrasion and adhesion. Alloy containing 2 wt% Ce, with the highest hardness and lowest K′ value, showed the greatest wear resistance.

Studies on friction and formation of transfer layer when Al–4Mg alloy pins slid at various numbers of cycles on steel plates of different surface texture

In the present investigation, various kinds of textures, namely, unidirectional, 8-ground, and random were attained on the die surfaces. Roughness of the textures was varied using different grits of emery papers or polishing powders. Then pins made of Al–4Mg alloys were slid against steel plates at various numbers of cycles, namely 1, 2, 6, 10 and 20 under both dry and lubricated conditions using an inclined pin-on-plate sliding tester. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. Surface roughness parameters of the plate were measured using an optical profilometer. It was observed that the coefficient of friction and formation of transfer layer during the first few cycles depend on the die surface textures under both dry and lubricated conditions. It was also observed that under lubricated condition, the coefficient of friction decreases with number of cycles for all kinds of textures. However, under dry condition, it decreases for unidirectional and 8-ground surfaces while for random surfaces it increases with number of cycles.

Laser surface modification of Al–4Cu–1Mg alloy for enhanced thermal conductivity

The feasibility of enhancing thermal conductivity of Al–4Cu–1Mg alloy by depositing 80Cu–20Mo coating using high-power lasers has been examined. Coatings of 667±2.5 μm thickness were formed with metallurgically sound interface. Results showed an 86% increase in the thermal conductivity of Al–4Cu–1Mg alloy due to laser-deposited 80Cu–20Mo alloy coating. This coating approach can potentially be used on low coefficient of thermal expansion metal matrix composites to enhance their thermal conductivity in electronic devices.

Preparation of Aluminum-Magnesium Alloys from Magnesium Oxide by Molten Salt Electrolysis Method

Aluminum-magnesium alloys were prepared from magnesium oxide by molten salt electrolysis method. MgF2-BaF2-LiF was taken as electrolysis.Since the density of MgF2-BaF2-LiF was high than aluminum liquid, upload cathode of aluminum liquid was used in the tests. Current efficiency during melting was more than 80%, and the maximum was up to 87.7%. Some amount of magnesium oxide flowed into electrolytic cell. The content of Mg in alloys increased gradually and up to maximum of 18.6%(w) with electrolyzing time. The experiment results revealed that the addition of KCl improved the physical-chemical property of the melten salt.

Influence of cooling rate on the precipitation microstructure in a medium strength Al–Zn–Mg alloy

Medium strength Al–Zn–Mg age hardening alloys are widely used when a low quench sensitivity is required, such as in welding applications. In this work we present a detailed characterization of the precipitate microstructures resulting from different quench rates from the solution treatment, and from the subsequent artificial ageing to the T6 state, in an Al–4.5Zn–1Mg (wt%) alloy. This work is carried out using differential scanning calorimetry, transmission electron microscopy and in situ small-angle X-ray scattering. It is shown that for quench rate between 5 and 200 °C/min substantial heterogeneous precipitation is observed, nucleated on dispersoids and on grain boundaries, the former being of much larger size than the latter. During subsequent ageing, it is shown that the precipitation kinetics in the material unaffected by the quench-induced precipitates is independent on the quench rate used.

Effect of gauge length in superplastic tensile tests

There is an incentive to obtain data on the mechanical behaviour of superplastic materials to model superplastic forming processes, in particular to help reduce forming times. The usual method involves tensile tests at elevated temperatures without extensometry. However, inhomogeneous deformation has a large effect on the apparent stress–strain behaviour and elongation to failure. Strain distributions have been measured in tensile specimens of superplastic Al–4·5Mg alloy with different gauge lengths, and on a non-superplastic Al–1Mn alloy, all tested at 530°C. There was considerable drawing-in of material from the specimen ends to the gauge in the superplastic alloy, but not in the Al–Mn material. The draw-in meant that the apparent elongation of the Al–4·5Mg alloy almost doubled when the gauge length to width ratio was reduced from 4 to 1 and the apparent stress–strain behaviour was also significantly affected by the gauge geometry.

Hypervelocity impact damage to Ti–6Al–4V meshes reinforced Al–6Mg alloy matrix composites

An Al–6Mg alloy matrix composite reinforced with Ti–6Al–4V meshes was fabricated by pressure infiltration method; its damage behaviors impacted by hypervelocity aluminum projectiles were investigated. Results showed that the thin Ti f/Al–6Mg composite target exhibits better protection efficiency and energy absorption ability than Al–6Mg alloy target. With projectile sizes increasing, bulge and spallation were observed on the back of the composite target. The Ti–6Al–4V meshes were tensed and deformed drastically in the spallation region, where micro-damages such as interfacial debonding and cracks were dominant. Shear localization was the primary failure characteristic for thin Al–6Mg alloy target. The adiabatic shear bands were observed near the crater of Al–6Mg alloy, not in Ti f/Al–6Mg composite target. It was ascribed to the Ti–Al interfacial bonding strength and the high temperature strength for Ti–6Al–4V alloy.

Phase stability of Cu 2Mg and CuMg 2 compounds against noncrystallizations analyzed with a plastic crystal model

The phase stabilities of Cu 2Mg and CuMg 2 compounds were analyzed for their noncrystallizations with molecular dynamics (MD) simulations based on the plastic crystal model (PCM), which includes a series of processes for random rotations of hypothetical clusters around their centers of mass, relaxation and annealing. The calculation results in terms of pair-distribution functions reveal that the Cu 2Mg alloy created with PCM tends to form in a crystalline structure, whereas the CuMg 2 alloy forms in a noncrystalline structure. MD simulations based on PCM are validated because they are consistent with the experimental results indicating that the compositions for the Cu 2Mg and CuMg 2 alloys are outside and inside the amorphous-forming composition range (AFCR), respectively. PCM is of great importance due to its agreement with the experimental data on AFCR, which has yet to be obtained using conventional MD methods through quenching from a liquid phase.

Effects of the Injection Temperature of N2 Gas on Pressureless Infiltration for Fabricating Al-Mg/Al2O3 Composites

Pressureless infiltration of molten Al−Mg alloys into particulate Al2O3 preforms has been known to occur only in a nitrogen atmosphere. In order to understand the pressureless infiltration mechanism of Al−Mg alloys into particulate Al2O3 preforms, nitrogen was injected at 25°C, 300°C, and 600°C. The higher the injection temperature of the nitrogen gas was, the lower the infiltration temperature of the molten Al−Mg alloys into the particulate Al2O3 preform was. Pressureless infiltration of the Al−6Mg alloy occurred at 700°C when the nitrogen gas was injected at 600°C. The formation of an Mg−N compound (Mg3N2) on Al2O3 particles, which improves wettability by decreasing the interfacial energy between the Al−Mg alloys and the Al2O3 particles, enabled the formation of the Al−Mg alloy/Al2O3 composite via pressureless infiltration. Increasing the injection temperature close to the melting point of the Al−Mg alloys appeared to enhance the formation of Mg3N2 on the surface of the Al2O3 particles.

Deformation behavior of Al–4Cu–2Mg alloy during cold upset forging

Upsetting of cylinders is a standard test which determines the ability of material to be forged either in cold or warm worked condition without cracking. In the present work, cylindrical specimens of aluminum–4% copper–2% magnesium alloy are upset between flat platens to study the metal flow at room temperature. Lubrication at the interface of the die/work piece and the specimen aspect ratio ( H 0/ D 0) are studied as process parameters. Lubrication minimized the barreling of lateral free surface. Microstructural studies reveal the non-uniform deformation within the specimen. This effect is pronounced with high friction and low aspect ratio. Machine Vision system using PC-based video recording with CCD camera is used to study the pre-drawn square grid deformation at the equatorial plane of the specimen. The system is used to measure the axial and circumferential strain components during deformation. Finite element analysis of cold upsetting process is carried out in both dry and lubricated conditions with aspect ratios of 1.0 and 1.5. Rigid-flexible contact analysis is performed for the forming process. When the stress values obtained from finite element analysis are compared to the measurement of grids using the Machine Vision system it is found that they are in close proximity.

Vibration fracture resistance of 5052H112 aluminum alloy processed by cold rolling and friction stirring

Abstract Hot-rolled Al–3Mg alloy processed by various cold-rolled reductions exhibited excellent vibration fracture resistance, however subsequent friction stirring did not endow better vibration fracture resistance than cold-rolled samples in spite of possessing microstructural refinement and homogenization. The D–N curve under a constant initial deflection amplitude (6.5 mm) also showed that the vibration fracture resistance of cold-rolled specimens increased as a result of the slower crack propagation rate. All samples used in this investigation showed a work hardening feature from the initial stage of the D–N curve, and the deflection amplitude tended to increase as the number of vibration cycles increased. During this ascending stage, slip band cracking and strain hardening in the vicinity of the main crack could be recognized. The D–N curve feature of the cold-rolled samples depicted a longer plateau region while the deflection amplitude was at its maximum. It is suggested that the dislocation tangles introduced by cold rolling can strengthen the matrix. As a result, the deflection amplitude drops could be associated with increasing the dislocation tangles due to prior cold rolling while the main crack achieved a critical crack length.

Wear properties of copper-coated short steel fiber reinforced stir cast Al–2Mg alloy composites

In the present investigation, wear properties on 2.5, 5 and 10 wt% copper-coated short steel fiber reinforced Al–2Mg alloy composites fabricated by stir casting process were carried out using pin-on-disc wear testing apparatus. The effects of sliding distance, applied load and wt% of fiber on the dry sliding behaviour were evaluated. Dry sliding wear tests at room temperature revealed that the wear rate of MMCs were significantly lower than alloy. The coefficient of friction and the wear rate also decreased with increasing fiber content. The worn surface and debris of specimens were examined under scanning electron microscopy (SEM) to find out the wear mechanism. SEM observations revealed that extensive microcracks occur on the surface of the alloy tested at lower loads. The growth of these microcracks eventually led to the delamination of debris from the alloy surface. The copper-coated steel fiber addition tended to reduce the plastic deformation in the surface layer there by reducing the occurrence of microcracking in the MMCs. The wear mechanisms of MMCs are dominated by oxidative wear at lower load but it changed to severe wear when applied load are increased. The composites containing 2.5 and 5 wt% of fibers exhibited a load dependent transition from mild to severe wear with increasing load. In case of 10-wt% fiber composites showed only mild wear even at higher applied load.

Effect of scandium on the microstructure and ageing behaviour of cast Al–6Mg alloy

Microstructural modification and grain refinement due to addition of scandium in Al–6Mg alloy has been studied. Transmission electron microscopy is used to understand the microstructure and precipitation behaviour in Al–6Mg alloy doped with scandium. It is seen from the microstructure that the dendrites of the cast Al–6Mg alloy have been refined significantly due to addition of scandium. Increasing amount of scandium leads to a greater dendrite refinement. The age hardening effect in scandium added Al–6Mg alloys has been studied by subjecting the alloys containing varying amount of scandium ranging from 0.2 wt.% to 0.6 wt.% to isochronal and isothermal ageing at various temperatures for different times. It is observed that significant hardening takes place in the aged alloys due to the precipitation of scandium aluminides.