ZA27 Alloy Research Articles

The effect of manganese on the microstructure and mechanical properties of zinc–aluminium based ZA-8 alloy

In this investigation, the effect of manganese as an alloying element in the range 0.01%–0.53 wt.%, on the hardness, 0.2% yield, tensile and impact strength, and creep properties of a gravity cast Zn–Al based ZA-8 alloy has been investigated. It was found that addition of Mn over the entire range of concentrations has a useful effect on the hardness of the alloy. Also, the 0.2% yield and ultimate tensile strength (UTS) of the samples did not change significantly with Mn additions up to 0.045 wt.% but decreased with a further increase in Mn content. Furthermore, the impact strength of the alloy improved with increasing Mn up to 0.045 wt.% and then decreased gradually with a further increase in Mn content. On the other hand, the creep resistance of the alloy increased continuously with increasing Mn content up to 0.53 wt.% Mn. Metallographic studies showed that addition of Mn resulted in microstructural modifications of the alloy involving the formation of complex intermetallic compound identified as MnAl6. The increase in creep resistance and decrease in tensile and impact strength were thought to have been caused by the changing morphology and amount of the intermetallic.

Effects of quench aging treatment on microstructure and tensile properties of thixoformed ZA27 alloy

The effects of quench aging heat treatment on microstructure and tensile properties of thixoformed ZA27 alloy were investigated. The results indicated that the microstructure of the alloy became into polygonal β phase particles after solid solution treatment at 350°C for 48 h. The β particles then decomposed into α and η phases which would coarsen during the subsequent aging at 150°C. It was observed that the Zn concentration in the β phase near the polygonal boundaries was higher than that within the β particles. As a consequence, both the decomposition speed of the former β phase and the subsequent coarsening speed were faster than those of the latter β phase. Thus, α and η phases near the boundaries were always coarser than those within the particles during aging. Owing to the coarsening, the ultimate tensile strength continuously decreased with increasing aging time. The percentage elongation increased up to 10 h, but decreased with aging time owing to bad deformation accommodation and low bonding strength between particles. Cracks initiated from some defects (e.g. inclusions and porosities) during tensile test, and the path for the cracks to propagation changed with the aging time.

Use of EBSD to identify phases in interdendrite region of a cast Zn–Al‐based alloy (ZA27)

Electron backscattered Kikuchi diffraction methodology was used to identify phases in the interdendrite region of an alloy ZA27. Two Zn-rich hexagonal close-packed structure phases eta and epsilon phases were distinguished using predetermined lattice parameters of the phases. In relation to studies of scanning electron microscopy and X-ray diffraction, electron backscattered diffraction results revealed that the Al-rich precipitates of the alpha phase were from decomposition of the eta'(T), and the four-phase transformation: alpha+epsilon--> T'+eta, had occurred in the epsilon phase after ageing at 150 degrees C for 8 h.

Compressive behavior and damping property of ZA22/SiC p composite foams

The ZA22 alloy composite foams reinforced by 10 vol.% SiC particles (ZA22/SiC p composite foams) were fabricated with the melt foaming route using CaCO 3 blowing agent in this paper. The compressive behavior and damping property of the composite foams were investigated. The results show that SiC particles dispersing in cell walls can alter the deformation mechanism of ZA22 foams. The plateau stress of the composite foams, therefore, fluctuated continually. The damping properties of ZA22/SiC p composite foams are obviously higher than those of ZA22 alloy and ZA22 foams. The addition of SiC particles can improve the damping capacity of ZA22 foams because SiC particles introduce multifarious interfaces and high-density dislocations in composite foams.

Electronic theory of interface characteristics of ZA27/CNT

The interface binding energy has been defined according to the atomic binding energy. The interface electronic structures of ZA27/CNT have been calculated by recursive method in zinc-aluminum composite reinforced by carbon nanotube. The microphysics of carbon nanotube distribution at grain boundaries of ZA27 alloy and the cause of weak interface binding in ZA27/CNT at electronic level were made clear. The research showed that the metal matrix has great effect on the density of states of carbon atoms on the nanotube, but the nanotube has little effect on the density of states of aluminum or zinc atoms in the matrix. The density of states of carbon on nanotube tends to become assimilated with matrix atoms and combine with the matrix, but as the assimilation degree is low, the interface binding strength is very weak. It is believed that similar property of atoms with matrix decorating or plated on carbon nanotube may help to reinforce the interface binding strength and improve the performance of ZA27 composite.

Characterisation of phase segregation during back extrusion of ZA27 semisolid alloy

Effort was made to characterise segregation tendency of mechanically stirred ZA27 alloy with back extrusion as a thixoforming process. At sufficiently high ram speeds, at which liquid phase flows forcefully, pooling of the heavy liquid phase owing to gravitational segregation contributes to homogeneity of back extruded products in terms of solid phase distribution. The amount of this contribution depends on the contact time of this liquid with solid skeleton during liquid exertion to the clearance. Hence, at high ram speeds, small rams which demand taller initial slugs are more efficient in minimising the segregation. However, in the case of low speed back extrusion tests, liquid impotency gives rise to higher performance of the ram which sooner induces combined flow of both phases and thus, thick rams are advantageous over thin ones.

Design of mechanical properties of a Zn27Al alloy based on microstructure dendritic array spacing

The present work focuses on the influence of the as-cast dendritic microstructure of a ZA27 alloy (Zn–27 wt%Al) on tensile mechanical properties. A low carbon steel chill was used in a unidirectional solidification experimental set-up in order to permit a wide range of dendritic spacings to be obtained along the casting. Experimental results include transient metal/mold heat transfer coefficients ( h i ), tip growth rate ( V L), secondary dendrite arm spacing ( λ 2), ultimate tensile strength ( σ U) and yield strength ( σ y) as a function of solidification conditions imposed by the metal/mold system. Experimental laws relating σ U and σ y with secondary dendrite arm spacing are proposed. It was found that both tensile properties increase with decreasing λ 2. A predictive theoretical dendritic growth model has been compared with the present experimental observations. Expressions correlating tensile properties, dendritic spacing and solidification thermal variables have been established. Such expressions permit the control of as-cast microstructures by manipulating casting variables, such as the cooling rate and the tip growth rate and can be used as an alternative way to design mechanical properties.

DRY SLIDING WEAR BEHAVIOUR OF FLYASH REINFORCED ZA-27 ALLOY BASED METAL MATRIX COMPOSITES

In the present investigation, an attempt has been made to evaluate the wear rate of ZA-27 alloy composites reinforced with fly ash particles from 1 to 3 wt% in steps of 1 wt%. The compo-casting method has been used to fabricate the composites using Raichur fly ash of average size 3-5 microns. The wear specimens are tested under dry conditions using a pin-on-disc sliding wear testing machine with wear loads of 20-120 N in steps of 20 N, and the sliding distances in the range of 0.5 km to 2.5 km. The results indicate that the wear rate of the composites is less than that of the matrix alloy and it further decreases with the increase in fly ash content. However, the material loss in terms of wear rate and wear volume increases with the increase in load and sliding distance, both in the cases of composites and the matrix alloy. An increase in the applied load increases the wear severity by changing the wear mechanism from abrasion to particle-cracking induced delamination wear. It is found that with the increase in fly ash content, the wear resistance increases monotonically. The observations have been explained using scanning electron microscope (SEM) analysis of the worn surfaces of the composites.

Phase Segregation Susceptibility of ZA27 Alloy at Different Shear Rates

Back extrusion technique was employed to characterize phase segregation tendency of mechanically stirred ZA27 alloy at different deformation rates. Variation of segregation intensity with ram diameter was found to follow opposite trends at low and high ram speeds. At sufficiently high ram speeds, small rams are of better performance in minimizing segregation whereas at low ram speeds, large rams result in less pronounced segregation. In addition, increasing ram speed invariably decreases segregation degree. Back extrusion at very high shear rates provided via a Drop Extruder Apparatus capable of displacing ram at speeds in excess of 1m/s results in production of very homogeneous products in terms of solid fraction as well as size distribution of globules.

EFFECT OF ANNEALING ON DAMPING CAPACITIES OF AS-CAST ZA27 ALLOY

ZA27 alloy was prepared by casting with permanent mold and then annealed at 250°C for 1—4h. The damping capacity of the alloy was measured using a testing apparatus based on the cantilever beam technique. It was found that the as-cast ZA27 alloy possesses high damping capacity with the value of 1.3 × 10−3 at 320Hz. After annealed at 250°C for 1h, the damping capacity decreases to 1.1 × 10−3 and then remains constant even when the annealing time is increased to 4h. The microstructure of the as-cast ZA27 alloy consists of large dendrites of Al-rich primary α-phases, eutectoid (α + η) and nonequilibrium eutectic phases (α + η + ɛ). After annealing at 250°C for the ɛ phase disappears due to dissolution into the matrix, and the spacing between the flakes of eutectoid increases. The further increase in the annealing time has little effect on the spacing. The damping mechanism of the alloy was discussed considering the thermoelastic damping and defect damping. The value of thermoelastic damping accounts only for 7%–8% in the overall damping in cantilever beam damping measurements and the damping capacity of the ZA27 alloy came mainly from defect damping.

A New Method for Production of Nondendritic Semisolid ZA27 Alloy

In this article, a new method for the production of nondendritic semisolid ZA27 alloy available for thixoforming was developed. The results indicated that a semisolid microstructure with small and spherical primary particles could be obtained when the alloy had been treated for 3 h at 370°C and then partially remelted at semisolid temperature of 460°C. This method could not only overcome some inevitable shortcomings resulting from using some present popular approaches but also simplify the procedure of thixoforming. The coarsening of dendritic arms through merging during solid solution treatment and then separating from the dendrites during partial remelting were the main methods by which such a microstructure was formed.

Comparison of the wear properties of modified ZA-8 alloys and conventional bearing bronze

In this study, an attempt has been made to examine the wear response of some modified Zn–Al based alloys and a conventional bearing bronze (SAE 660) at the sliding speeds of 0.5 ms −1, 1 ms −1, 1.3 ms −1, 1.7 ms −1 and 2 ms −1 using applied load of 30 N and 45 N. The standard ZA-8 alloy and modified with 1% Pb, 1% Sn and 1% Cd alloys have been subjected to a pin-on-disc wear test under dry condition. A conventional bearing bronze has also been subjected to identical tests with a view to assess the working capability of the modified Zn–Al based alloys with respect to existing ones. The results have shown that the ZA-8 alloy and modified with Pb, Sn and Cd alloys revealed higher wear resistance when compared with bearing bronze. In addition, wear resistance of ZA-8 based alloys increased with increasing sliding speed up to 1.7 ms −1 for 30 N and 1.3 ms −1 for 45 N, respectively. But it decreased with increasing sliding speed. The addition of Pb to the ZA-8 alloy increased wear resistance of the alloy for all of the sliding speeds at 30 N and 45 N, while the addition of Cd increased wear resistance of the ZA-8 at 45 N. But Sn alloying element caused worse wear resistance for ZA-8 alloy. On the other hand, the friction coefficients of ZA-8 and modified alloys are higher than that of the bearing bronze. Metallographic studies showed that the addition of Pb, Sn and Cd resulted in modifying on the microstructure of ZA-8 alloy.

Microstructural changes inside the lamellar structures of alloy ZA27

The microstructural changes inside the lamellar structure of the cast and aged alloy ZA27 were studied using TEM, XRD and SEM techniques. Using TEM, the network of transitional phase η m ′ was determined to be of an fcc crystal structure inside the lamellae η phase during ageing at 150 °C. The mechanism of the decomposition of the η phase lamellae can be summarized as follows: η → η m ′ + η′ → α + η. The adjacent co-existence of the ε phase and the T′ phase inside the α phase lamellae confirmed that a four phase transformation, α + ε → T′ + η, had occurred during the prolonged ageing.

Effects of processing parameters on microstructure of thixoformed ZA27 alloy

In this paper, the effects of processing parameters on microstructures of thixoformed ZA27 alloy cylindrical rods were investigated. The results indicated that the microstructure of the formed rod was basically uniform except that of the section near the inner gate. But the detailed microstructure observation or quantitative examination showed that the primary particle fraction slightly decreased along the axial direction but it relatively more obviously decreased along the radial direction. The primary particle size increased and the primary particle fraction decreased with the increase of reheating duration. Both the size and fraction of primary particles decreased with elevating the reheating temperature and increased with increasing the die temperature. The secondary solidification began with the direct growth of the secondary primary phase on the surface of the primary α′ particles and completed by forming lamellar eutectics. The secondarily solidified structure was significantly affected by die temperature while the other two parameters, reheating temperature and reheating time had no obvious effect.

Effect of rectangle wave pulse current on solidification structure of ZA27 alloy

The effect of rectangle wave pulse current on solidification structure of ZA27 alloy was studied. The results show that the wave pattern relies on the frequency range of harmonic wave and the energy of pulse current within the frequency range of pulse current. Imposed pulse current could induce the solidification system to oscillate. The frequency range and the relevant energy distribution of pulse current exert an influence on the amount of atoms involved for forming critical nucleus, the surface states of clusters in melt, the oscillating state of melt on the surface of clusters, the active energy of atom diffusion, the frequnce response of the resonance of bulk melt and the absorbability of the solidification system to the external work. Rectangle wave pulse current involves rich harmonic waves; the amplitudes of high order of harmonic waves are higher and reduce slowly, so it has a better effect on inoculation and modification.

Aging microstructural characteristics of ZA-27 alloy and SiC p/ZA-27 composite

Abstract The aging characteristics of as-quenched microstructures of ZA-27 alloy and SiC p/ZA-27 composite(ZMC p) were investigated using SEM, EDS and TEM. The structure, morphology and size of sub-grains in primary dendrite in ZMC p continuously change during aging process. Little tiny spherical Zn-rich η phase distributes in the dendrite. Amount of transitional α′ phase, well coherent with equilibrium α f phase, in SiC p-neighboring dendrite edge zone is less than that in dendrite center zone. Both eutectic and peritectic β phase transform into lamellar α and η phases, obeying [ 2 ¯ 113 ] η / / [ 110 ] α , and ( 002 ) α / / ( 1 1 ¯ 01 ) η . In the like-eutecticum of ZMC p, less amount of β phase and decomposition products are found. The size of α phase decomposed from peritectic β phase in ZMC p is obviously larger than that in the monolithic alloy. The lamella decomposition of β phase beside SiC p is evidently more rapid than that in the alloy. SiC particulates strongly accelerate neighboring β phase decomposition in aging process.

Ordering and interaction of Fe and RE atoms on grain boundaries in ZA27 alloys

In order to reveal the behaviors of Fe and RE atoms on grain boundaries in ZA27 alloy theoretically, the atomic structure model of high angle grain boundary of α phase in ZA27 alloy was set up by using the concept of coincidence-site lattice(CSL). The electronic structure (state density, Fermi energy level, structure energy) of grain boundary was calculated using the recursion method. The clustering energy of alloying atoms was defined by the structure energy of grain boundary, and the clustering energies of Fe or RE atoms on grain boundary was calculated. The calculated results show that: the clustering energy of Fe or RE atoms gathered on grain boundary in ZA27 alloys is positive, so they can not form clusters and have the ordering tendency. Fe and RE atoms prefer to form steady inter_metallic compounds, and can form the negative electricity center on grain boundary in ZA27 alloys, thus reducing the Fermi energy level of grain boundary.

Die-filling process during the thixoforming of a ZA27 alloy cylindrical rod

The die-filling process during thixoforming of a ZA27 alloy cylindrical rod was deduced by analyzing microstructural characteristics in the semi-solid ingot prior to and after forming, and by analyzing the phenomena occurring during this thixoforming. These characteristics referred to some constituent segregation, such as a liquid-phase segregation and an inhomogeneous distribution of primary solid particles. The results indicated that the die-filling process could be properly deduced by using the method developed in this paper. The inhomogeneous distribution of primary solid particles in the formed rods mainly resulted from the inhomogeneous distribution in the semi-solid ingot. The detailed distribution was determined by the sequence of the die-filling. However, the aforementioned liquid segregation was mainly attributed to the die-filling process. The sequence of the die-filling process was from the bottom of the cylindrical cavity to the top and from the edge to the inner part of the cavity.

Mechanical properties of severely deformed ZA-27 alloy using equal channel angular extrusion

As cast ZA-27 alloy was subjected to equal channel angular extrusion (ECAE) with up to four passes using three different processing routes, and its mechanical properties (strength, hardness, ductility and extrusion load) were evaluated. The changes in the microstructure were also investigated. The ECAE was found to be quite effective in enhancing the mechanical properties of ZA-27 alloy. The strength and hardness of the alloys increased after the first ECAE pass followed by a gradual decrease with further passes for all processing routes. The elongation to failure, however, exceptionally increased with increase in the number of passes for all processing routes. Combined high strength and good ductility were obtained in the alloy after the first pass. The strength and maximum extrusion load showed similar trends with the number of passes for all processing routes.

Evolution of as-cast and heat-treated microstructure of a commercial bearing alloy

The present study involves the microstructural changes of a zinc–aluminium alloy (ZA27) by nickel, a high melting point element, and the commercial master alloys, Al–5Ti–1B and Al–5Sr. The evolution of as-cast microstructure and the effect of heat treatment on the as-cast microstructure and hardness have been presented in detail. The addition of Ti, B and Sr as master alloys results in significant refinement in the dendrite structure of the ZA27 alloy. The addition of Ni to ZA27-based alloy results in the formation of Ni-aluminides as rod as well as blocky-shaped particles. High amount of Ni (2wt.%) refines the dendritic structure significantly.