Zinc Aluminium Alloy Research Articles

Al-Doped ZnO Films Deposited by Reactive Magnetron Sputtering in Mid-Frequency Mode with Dual Cathodes

Aluminum-doped zinc oxide (AZO) films were deposited on heated (300°C) glass substrates by reactive mid-frequency (mf, 50 kHz) magnetron sputtering using dual magnetron cathodes with aluminum–zinc alloy targets. In order to keep the very high deposition rate, reactive gas control using plasma emission was carried out to stabilize the discharge in the “transition region” of the reactive sputtering system. The highest deposition rate for the transparent conductive AZO films by this dual magnetron sputtering (DMS) system was 290 nm/min, which was higher than that for the conventional reactive sputtering system by one order of magnitude. The lowest resistivity of the AZO film was 3.9×10-4 Ω cm. The structure and electrical properties of the films could be controlled systematically by the reactive gas control system in the transition region.

Effect of Ni on the wear behavior of a zinc-aluminum alloy

In this investigation, an attempt has been made to examine the effect of Ni on the wear response of a high-aluminum zinc alloy. The alloy has been modified with 0.3 and 0.9 wt% Ni, and wear tests have been carried out at sliding speeds of 3.925 and 6.54 m/s. The wear characteristics have been correlated with their microstructural features. The unmodified alloy exhibits inferior wear behavior with the increase in sliding speed. The improved wear response of the modified alloys is due to the presence of Ni3Al phase formed throughout the matrix. Moreover, the improvement of the modified alloy is more significant at the higher speed of sliding and also with the increase in Ni content. This study indicates that it is possible to develop modified versions of high-aluminum zinc-based alloys having much improved wear characteristics; the information gains special attention in view of the high speed of sliding used in this study.

AFM AND XPS CHARACTERIZATION OF ZINC–ALUMINUM ALLOY COATINGS WITH ATTENTION TO SURFACE DROSS AND FLOW LINES

Surfaces of various zinc–aluminum alloy (Zn–Al) coated steel samples are studied with attention to foreign surface dross by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS/ESCA). AFM topographic maps of zinc–aluminum alloy surfaces free of dross reveal the perfect nanoscale details of two kinds of dendrites: branched and globular. In all magnifications the dendrites appear smooth and, in general, very clean. XPS analysis of the extreme surface of a Zn–Al sample reveals Al, Zn, Si and O as the main components. The XPS results show no segregation or separation of phases other than those indicated by the ternary Al–Zn–Si diagram. For surfaces of Zn–Al plagued with impurities, high resolution AFM topographic maps reveal three situations: (1) areas with well-defined dendrites, relatively free of dross; (2) areas with small, millimeter-sized black spots known as dross; and (3) areas with large black stains, known as flow lines. Dendrite deformation and dross accumulation increase notably in the neighborhood, apparently clean to the naked eye, of dross or flow lines. XPS results of areas with dross and flow lines indicate unacceptable high concentration of Si and important Si phase separation. These results, in the light of AFM work, reveal that dross and flow lines are a consequence of a high local concentration of Si from high melting point silica and silicate impurities in the Zn–Al alloy source.

The machinability and tribological characteristics of aluminum alloys with improved elevated temperature properties using rapidly solidified powder

In this investigation the tribological characteristics of rapidly solidified Al–8Fe–4Ce with improved elevated temperature properties were studied. Such characteristics were compared with cast aluminum–silicon alloy and cast zinc–aluminum alloy. These materials included Al–13Si, Zn–35Al, Zn–35Al–Si, Zn–35Al–3.75Si and Zn–35Al–5.8Si. The wear rates of all materials were tested on a crossed-cylinders wear machine against 440C stainless steel counterface lapped by random abrasion using diamond paste to the desired average surface roughness. The effects of sliding distance on both the worn volume and the coefficient of friction were examined. The aluminum–iron–cerium alloy (Al–8Fe–4Ce) showed the lowest wear rate. The experiments were then extended on this material to examine the effect of varying the applied load and sliding speed on its wear rate. It was found that increasing the applied load increased the wear rate while it was slightly sensitive to the change in sliding speed. As the wear results showed that the Al–8Fe–4Ce alloy has the lowest wear rates, its machinability during turning operation was studied. Statistically-based experimental design (response surface methodology) using central composite second-order rotatable design technique was used to improve the experimentation design without loss of accuracy of the results. The interaction of cutting parameters (cutting speed, feed rate and depth of cut) was examined and their effect on the average surface roughness was reported. It was found that employing a combination of high cutting speed and small depth of cut with small feed rate causes a significant reduction in Ra. The data were represented in three-dimensional and contour graphs for selecting the appropriate machining conditions required to achieve desired values of surface roughness.

Cut edge corrosion mechanisms in organically coated zinc–aluminium alloy galvanised steels

Organically coated galvanised strip steel materials are increasingly important as construction materials. The effects of magnesium additions to the zinc spelter on the microstructure and cut edge corrosion mechanism of zinc aluminium alloy galvanising coatings on strip steels have been found to be significant. Galvanised specimens were prepared on 0.7 mm steel substrates using a hot dip bath composition of near eutectic 4.2 wt-% aluminium-ca. 95 8 wt-% zinc and trace levels of magnesium. Increasing the magnesium content in the metallic coating from 0.01 to 0.05 wt-% leads to the formation of significant areas of subsurface, dendritic, pro-eutectic zinc rich phases. The metallic coating substrates were over coated with asymmetric thicknesses of a 200 μm PVC based coating on one side and a 15 μm polyester coating on the other producing a range of model organically coated substrates identical in every way except for the magnesium level in the metallic coating. The kinetics and mechanism of cut edge corrosion in 5 vol.-%NaCl of these model systems have been investigated using the scanning vibrating electrode technique (SVET). The SVET data have shown that the increasing coating heterogeneity with increased magnesium content leads to increasing numbers of active and intense anodes on the exposed surface of the metallic coating at the cut edge. At magnesium levels of < 0.03 wt-%, asymmetry in the thickness of the organic coating induced localisation of anodic activity near to the thicker (PVC) organic layer, and of cathodic activity localised primarily on the steel/galvanising layer adjacent to the thinner (polyester) organic coating. However, as the magnesium content of the metallic coating was increased (to 0.04 and 0.05 wt-%) the location of anodic and cathodic activity was found to become independent of the geometry of the organic coating. Whilst the number of active anodes on the 20 mm exposed edge was found to be identical for both of the latter magnesium levels those in the 0 05 wt-%Mg specimen were more persistent. In the case of the 0 04 wt-%Mg specimen, 13 of the 21 active anodes deactivated over the first 12 h of immersion whereas with the highest magnesium level deactivation was only observed for 5 of the 21 anodes. Those that remained active in the latter specimen also had significantly greater levels of anodic activity. This appears to be related to interlinking between particles of the pro-eutectic zinc rich phase in specimen of the highest magnesium level, leading to crevice corrosion. The consequence of the microstructural changes induced by trace Mg additions in that the SVET measured total zinc losses over the 24 h exposure period increasing from 28 μg (with 0.01 wt-%Mg), to 44 μg (0.02 wt-%Mg), 61 μg (0.03 wt-%Mg), 67 μg (0.04 wt-%Mg) and 223 μg (0.05 wt-%Mg).

AFM AND XPS Characterization of Zinc-Aluminum Alloy Coatings with Attention to Surface Dross and Flow Lines

AFM AND XPS Characterization of Zinc-Aluminum Alloy Coatings with Attention to Surface Dross and Flow Lines

Three-body abrasion of a cast zinc–aluminium alloy: influence of Al 2O 3 dispersoid and abrasive medium

Three-body abrasive wear characteristics of a cast zinc–aluminium alloy — 10 wt.% alumina particle composite have been analysed in the present investigation. Silicon carbide, sand and zircon particles were used as the abrasive media. In order to see the influence of alumina dispersoid particles on the abrasive wear behaviour, the similarly processed matrix alloy was also tested under identical conditions. The composite exhibited less wear rate than the matrix alloy irrespective of the test conditions. This was attributed to the wear resistance offered by the hard dispersoid phase, thereby protecting the softer matrix. Further, the SiC abrasive caused maximum wear rate while the specimens experienced the minimum when abraded against zircon particles; sand particles led to intermediate wear response. Wear rate of the samples decreased progressively with distance until a steady-state value was attained. Abrasion-induced work hardening was thought to be responsible for the decreasing wear rate with distance. Increased hardness of the (subsurface) regions as compared to that of the bulk also supported the view. Further, the rate of reduction in wear rate with distance was relatively more for the matrix alloy than the composite. This behaviour was more clearly visible and, at the same time, the extent of reduction in the wear rate with distance was maximum in the case of the SiC abrasive. Sand was observed to be more damaging than zircon despite its less hardness (than the latter). This could be owing to the sharp/angular shape of the sand abrasive in comparison to the round shaped zircon particles suggesting the predominant effect of the particle shape over the hardness of the abrasive. More severe loading conditions led to larger wear rates because of the greater depth of cut and more surface/subsurface damage. Observed wear response of the samples has been supplemented with the features of wear surfaces and subsurface regions. The latter also enabled an understanding of the operating wear mechanisms.

Development of rapidly solidified (RS) magnesium–aluminium–zinc alloy

Applications of magnesium alloys in the aerospace industry are limited because of their poor mechanical properties, corrosion resistance and workability. Refinement of microstructure through rapid solidification processing is one of the highly potential approaches to overcome these limitations. In the present study, the technology of processing of rapidly solidified (RS) ribbons in Mg-9%Al-1%Zn-0.2%Mn alloy has been established using melt spinning technique. The effect of wheel speed on thickness and microhardness of the ribbons is presented. Microhardness is found to increase with the wheel speed. It is further observed that microhardness of the ribbons increases with the heat treatment temperature upto 200°C and thereafter it starts decreasing. Precipitation of the intermetallic phase Mg 17Al 12, at temperatures upto 200°C is found to prevent the grain growth and improve the properties of the ribbons. This in-turn reveals that the temperature for secondary processing of RS ribbons in Mg-9%Al-1%Zn-0.2%Mn alloy should not exceed 200°C in order to retain the benefits of rapid solidification processing.

Localized Corrosion Behavior in Aluminum-Zinc Alloy Coatings Investigated Using the Scanning Reference Electrode Technique

Abstract The scanning reference electrode technique (SRET) has been used to determine the influence of Al content on the kinetics of localized corrosion processes occurring on the intact surface of Al-Zn alloy-coated steel. Three commercial hot-dipped coatings were investigated: Galvatite (0.15%Al-Zn), Galfan (4.3%Al-Zn), and Galvalume (55%Al-Zn). All three exhibited strongly localized patterns of anodic metal dissolution when freely corroding in aerated aqueous chloride electrolyte. The currents emerging from discrete anodic sites and the mean active lifetime of the same sites decreased markedly with increasing Al content in the coating. Conversely, the total number of discrete anodic sites becoming initiated over a 24-h period was greater for the coatings with higher Al content. Anodic sites on the 0.15%Al and 4.3%Al coatings showed metal dissolution but no evidence of dealloying. However, anodic sites on the 55%Al coating exhibited local dezincification and porosity development. In this paper, corrosio...

Characterization of a non‐organofunctional silane film deposited on Al, Zn and Al–43.4Zn–1.6Si alloy‐coated steel

AbstractTime‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used to analyse the interface between a non‐organofunctional silane and three different metal substrates (aluminium, zinc and an aluminium–zinc alloy). Ion etching using Ga+ ions was used to expose the interfacial region. Ion fragments from the samples were examined carefully where supposed metal–oxygen–silicon ion fragments should appear in the mass spectra. From high mass resolution spectra it was concluded that there exists an AlOSi+ ion fragment at nominal mass m/z = 71 amu on the aluminium and aluminium–zinc alloy substrates and a ZnOSi+ ion fragment at nominal mass m/z = 108 amu on the zinc and aluminium–zinc alloy substrates. These results are further enhanced by the fact that the characteristic ion pattern of ZnOSi+‐type ion fragments, composed of different naturally stable zinc and silicon isotopes, in the mass range m/z = 108–112 amu showed the expected relative peak height relations.The presence of these metal–oxygen–silicon ion fragments is a strong indication that chemical interaction between the silane and the metal substrates exists and that the nature of this interaction is due to the formation of a covalent bond between the silane and the metal substrate. Copyright © 2001 John Wiley &amp; Sons, Ltd.

An Investigation of the Effects of Magnesium Levels on the Kinetics and Mechanism of Cut Edge Corrosion in Organically Coated Zinc Aluminium Alloy Galvanised Steels

SUMMARYThe scanning vibrating electrode technique (SVET) has been used to study the effect of variation in magnesium levels (0·01-0·05%) on the kinetics and mechanism of cut-edge corrosion in zinc aluminium alloy, galvanised steel samples over-coated with asymmetric thicknesses of organic coatings, immersed in 5% aqueous sodium chloride. Experimental samples were prepared on 0·7 mm steel substrates with a hot dip bath composition of near eutectic 4·2% aluminium/ca. 95·8% zinc and varying trace levels of magnesium ranging from 0·01 to 0·05%. Organic coating asymmetry was induced by over-coating the metallic coated substrates with a 200 μm PVC based coating on one side and a 15 μm polyester coating on the other. SVET data have shown that with magnesium levels of <0·03% organic coating asymmetry caused localisation of anodic activity proximal to the thicker (PVC) organic layer and cathodic activity localised primarily on the steel/galvanising layer proximal to the thinner (polyester) organic coating. This has been attributed to a form of differential aeration corrosion associated with reduced oxygen access to the zinc layer proximal to the thicker organic coating. However, as the magnesium content of the metallic coating was increased (to 0·04% and 0·05%) the location of anodic and cathodic activity was found to become independent of organic coating geometry. The increasingly intense focal anodic attack at the exposed cut edges, at these higher magnesium levels, was found to be directly related to the formation of significant areas of sub-surface, dendritic, pro-eutectic zinc phases. This highly heterogeneous coating metallurgy overrides the effects of differential aeration corrosion driven by organic coating asymmetry that is the dominant mechanism at lower magnesium levels.

Abrasive wear behaviour of zinc-aluminium alloy - 10% Al2O3 composite through factorial design of experiment

Two body abrasive wear behaviour of a zinc-aluminium alloy - 10% Al2O3 composite was studied at different loads (1–7 N) and abrasive sizes (20–275 μm) as a function of sliding distance and compared with the matrix alloy. The wear rate of the composite and the matrix alloy has been expressed in terms of the applied load, abrasive size and sliding distance using linear factorial design approach. The study suggests that the wear rate of the alloy and composite follow the following relations: $$\begin{gathered} Y_{{\text{alloy}}} = 0.1334 - 0.0336x_1 + 0.0907x_2 + 0.0296x_1 x_2 + 0.0274x_2 x_3 - 0.0106x_3 x_1 \hfill \\ {\text{ }} - 0.0201x_1 x_2 x_3 \hfill \\ Y_{{\text{comp}}} = 0.0726 - 0.028x_1 + 0.062x_2 + 0.03x_3 - 0.024x_1 x_2 + 0.028x_2 x_3 - 0.016x_3 x_1 \hfill \\ {\text{ }} - 0.014x_1 x_2 x_3 \hfill \\ \end{gathered}$$ where, x1, x2 and x3 are the coded values of sliding distance, applied load and abrasive size respectively. It has been demonstrated through the above equations that the wear rate increases with applied load and abrasive size but decreases with sliding distance. The interaction effect of the variables exhibited a mixed behaviour towards the wear of the material. It was also noted that the effect of load is less prominent for the composite than the matrix alloy while the trend reversed as far as the influence of the abrasive size is concerned.

Effect of microstructure on the sliding wear performance of a Zn–Al–Ni alloy

Some observations pertaining to the sliding wear characteristics of a zinc–aluminium alloy containing nickel under varying material and test conditions have been reported in this investigation. Dry sliding wear tests were conducted on as-cast and heat-treated zinc-based alloy pins using a pin-on-disc machine. A steel disc was employed as the counterface. Sliding speeds adopted were 0.42, 2.68 and 4.60 m/s while the traversal distance was fixed at 500 m. Wear tests were conducted at different pressures using separate pins in each case. Seizure pressure of the pins (prior to traversing the sliding distance of 500 m) was determined at each speed. Wear rate and the extent of frictional heating increased with pressure and speed whereas seizure pressure practically followed a reverse trend. The wear rate versus pressure plot of the as-cast alloy pins assumed two slopes at the lowest speed wherein low slope (indicating the occurrence of mild wear situation) was noticed initially. This was followed by the attainment of a higher slope suggesting severe wear condition at increased pressures. At higher speeds, one slope only (identical to the higher slope at the minimum speed) was noted. Wear rate versus pressure plots of the heat-treated alloy pins followed a trend similar to the as-cast ones except that two slopes were noted up to the intermediate speed in the former case. Heat treatment changed the as-cast dendritic structure of the zinc-based alloy into the one with an improved uniformity of the distribution of various microconstituents, the nickel containing phase remaining practically unaffected. Softening of the (as-cast) alloy was also observed as a result of the heat treatment. However, in spite of reduced hardness, the heat-treated alloy pins attained improved wear behaviour (i.e. reduced frictional heating and low wear rate) over the as-cast ones irrespective of the test conditions. This was attributed to a more uniform distribution of microconstituents and reduced cracking tendency of the alloy as a result of the heat treatment. The alloy pins also attained better seizure pressure in heat-treated condition comparing with the as-cast ones at all the speeds except the maximum for the same reasons. A reversal in the trend at the maximum speed was thought to be due to the over-softening of the already softened (heat-treated) alloy pins under the influence of large frictional heat generated at the (maximum) speed. Under the circumstances, the heat-treated alloy pins tended to adhere/fuse with the disc extensively while this tendency was relatively less for the as-cast ones in view of their higher hardness. Further, the extent of the negative influence of cracking tendency reduced allowing thermal stability to predominate the wear behaviour of the as-cast alloy pins in this case. The factor led to somewhat higher seizure pressure of the (as-cast) alloy pins at the maximum speed comparing with the heat-treated ones. Low wear rates correlated with less damage to the worn surfaces and to the regions below the worn surfaces and finer debris formation. Seizure led to severe damage to the worn surfaces and to the regions below the worn surfaces while the debris formed was quite bulky and coarser.

Microstructure and Wear of Zinc-Aluminium Alloys: Influence of Secondary Processing and Alloy Composition

Microstructure and Wear of Zinc-Aluminium Alloys: Influence of Secondary Processing and Alloy Composition

Tribological behaviour and microstructure of sintered zinc-aluminium alloys : L.Wen et al. (South China University of Technology, China.)

Tribological behaviour and microstructure of sintered zinc-aluminium alloys : L.Wen et al. (South China University of Technology, China.)

Sliding wear response of a zinc-aluminum alloy as affected by SIC particle dispersion and test conditions

Sliding wear response of a zinc-aluminum alloy as affected by SIC particle dispersion and test conditions

Fabrication of graded titanium-alumina by dry jet spraying of powder: H.Tanizaki et al. (Nisshin Steel, Ichikawa, Japan.) J. Jpn Soc. Powder Powder Metall., vol 44, no 4, 1997, 334–339. (In Japanese.)

Corrosion of a commercial two-phase eutectoid zinc-aluminium alloy modified by 2% Cu (Zinalco™) was performed at high temperature in a dry fluorine environment. This environment was kept at a pressure of 103 mbar for 100 and 300 h. The exposed samples were studied by resonant nuclear reaction, Auger electron spectroscopy, scanning electron microscopy and X-ray diffraction. The Knoop micro-hardness of the samples was measured before and after the exposure. Intergranular corrosion of the zinc-rich phase that tends to consume the material is observed, while the aluminium bonds to the fluorine forming a superficial AlF3 compound.

The morphology of cast zinc-based alloy reinforced by spheroidal silicon phase and its wear resistance

This paper deals with the influence of silicon phase on the wear resistance of zinc-aluminum alloy. In order to improve the wear resistance performance of ZA27 alloy under the conditions of dry friction, Si was added. It was discovered that the primary silicon phase changes from a block shape into a spheroidal one by the modification of the alloy with a compound agent containing sodium. Scanning electron microscope images (SEM) showed that the spheroidal silicon phase is a polyhedron from which needle-like eutectic silicon forms. The result of dry-friction testing indicated that this may be firmly embedded in the Zn-Al matrix and thus cannot be exfoliated during friction. The zinc-aluminum alloy reinforced by spheroidal silicon phase was found to have an increased wear resistance performance.

Quantum-chemical simulation of selective dissolution of brass and zinc-aluminum alloy

We theoretically study the selective dissolution of α-brass and a zinc-aluminum alloy by a semiempirical cluster calculation. A predominance of desorption of ions from the metal surface is shown and described. The effect of elastic deformation on selective dissolution is established.

Hardness of aged ZA-27/short glass fibre reinforced composites

This present investigation studies the effects of artificial aging on the hardness of cast ZA-27 zinc–aluminium alloy composites containing short glass fibres of diameter 4–6 μm, length 0.4–0.6 mm and contents of 1, 3 and 5% by weight. The age-hardening characteristics of the unreinforced ZA-27 alloy as well as of the glass fibre-reinforced composite materials were determined using hardness measurements. The aging temperatures were 75, 100 and 125°C, respectively and the aging durations were 6, 12 and 18 h, respectively. The results show that for any particular glass fibres content and aging temperature, hardness seems to increase monotonically with aging time, although it probably tends towards an asymptotic value. For the unaged composites, glass fibre content plays a significant role in determining their hardness values, whereas for all the aged composites, their hardness values are not so dependent on glass fibre content.