Fracture and mechanical properties of steel fibre reinforced Zn–5Al (Zamak 5) alloy

Abstract

Steel fibre reinforced Zn–5Al alloy (Zamak 5) metal matrix composite beams with different volume fractions of steel fibres were produced with varying notch to depth ratios. The fracture and mechanical properties of the specimens were investigated for their mode I fracture behaviour using three point bending tests under static loading at room temperature. Steel fibres with contents of 1, 2 and 3% of the total volume of Zn–5Al alloy were used as matrix materials. The critical stress intensity factor was determined using the initial notch depth method.     

Microstructure and strength of a squeeze cast aluminium piston alloy composite reinforced with alumina short fibre using Al2O3 binder

Abstract

Alumina short fibre preforms were fabricated using an Al₂O₃ binder and infiltrated with aluminium piston alloy melt by squeeze casting. Al₂O₃ binder is thermodynamically more stable than the conventional SiO₂ binder and reduces the fibre/matrix interfacial reaction. The effects of fibre volume fraction, temperature and heat treatment on the yield strength and tensile strength of the composite were investigated. The Al₂O₃ binder provided a satisfactory interfacial bond between the fibre and the matrix without any interfacial reaction or fibre damage. Aging behaviour was not changed by reinforcement. At every temperature, the composites showed the highest strength with a fibre volume fraction of 18%. The strength of the composite was improved by T6 heat treatment. Examination of the fracture surfaces and calculation of the tensile strength using the rule of mixtures indicated that the 18% fibre reinforced composite had a strong interfacial bond even at high temperatures.     

Improving vibration weld joint strength through process and equipment modifications

Abstract

Vibration welding is a process used to join thermoplastic components. Currently, under optimised low pressure welding, the weld strength of butt joints of unreinforced polymer can be equivalent to the strength of unwelded material. However, in short glass fibre reinforced polymer, the optimised weld strength is significantly lower than that of unwelded material and is closer to the strength of the resin matrix. This lower strength is attributable to the unfavourable orientation of the short glass fibres in the weld zone. The fibres tend to align parallel and in the plane of the weld zone and thus provide no reinforcement in the direction perpendicular to the weld zone. In the present work the impact of various modifications to the existing vibration welding technology was examined, with the objective of increasing the current achievable weld strength of glass reinforced nylon. The introduction of a secondary vibratory motion perpendicular to the weld plane during welding resulted in strengths 20% higher than those of samples welded using the standard vibration welding process.     

Temperaturbeständige faserverstärkte Verbundwerkstoffe

Temperature resistant fibre reinforced laminates Containers for liquids and pressurized gases as well as reaction vessels and autoclaves are made preferentially of steel even nowadays. Because of the relatively high specific weight of steel such containers have often a weight of several tons and require expensive and heavy su ports or suspensions. In order to save weight and thus also cost, materials are required which have higher tensile strength and lower specific weight than steel. Such materials are the fibre reinforced materials with plastic or light metal matrix. In addition to glass fibre reinforced materials, steel wire reinforced plastics will probably gain on importance. Because of the higher strength of the steel wires by comparison to conventional glass fibres the metal reinforced materials have the same tension length (i.e. the ratio strength: specific weight) as glass fibre reinforced materials. Aluminium alloys reinforced with steel wire yielded strength values up to five times the value measured on the base material. With a view to low weight construction the reinforcement of aluminium by boron fibres is of particular interest, the specific weight of the latter (2.7 glcm3) being about equal to that of the matrix material. A feature of particular importance to chemical industry is the fact that the mechanical properties of glass, too, can be improved by steel wire reinforcement. The flexural strength of glass specimens has been increased by steel fibres to 9 times the original value. The glass coated steel wire used for manufacturing reinforced glass is obtained according to a special process developed by Battelle Institute.     

Influence of fibre interconnections on the thermomechanical behaviour of metal matrix composites consisting of a Zn–Al alloy reinforced with steel fibres

Interconnected fibre networks presenting transverse isotropic symmetry with variable fibre interconnectivity were prepared by sintering assemblies of low carbon steel fibres. The strength and stiffness of these fibre preforms was found to increase very much when increasing sintering temperature or sintering time. Squeeze cast composites were prepared by infiltrating these preforms with alloy ZA8. Creep tests and tensile tests were carried out at 150°C. Both the creep strength and the back-flow strains at unloading drastically increase with increasing preform sintering temperature or time. Also thermal expansion is much affected by fibre interconnectivity. Especially, during cooling, the matrix dilatation strains brought about by thermal mismatches increase with increasing fibre interconnectivity. These results demonstrate that plastic and viscoplastic behaviours of network reinforced composites depend on the mechanical properties of the network as a whole.     

Aging of cast Ni-base heat resisting alloy

Abstract

The behaviour of a Ni-base heat resisting alloy during aging was studied by mechanical testing and by optical and electron microscopy in samples aged for up to 6 weeks at 750°C. The as cast microstructure consists of an austenitic matrix and a network of two types of primary carbide (chromium and niobium). As aging proceeds, the main changes detected were precipitation of secondary chromium carbides and decomposition of primary niobium carbide in Ni rich silicide. The primary chromium carbides were largely unaltered. The mechanical tests indicate that these phenomena degrade the properties of the material.     

Microstructure and wear behaviour of pulse electrodeposited alumina nanoparticle reinforced Co–W nanocomposite coatings

Abstract

The microstructure and wear behaviour of alumina nanoparticle reinforced Co–W alloy coatings have been investigated for potential replacement of hard chrome coatings. The composite coatings were pulse electrodeposited on steel substrates using a citrate bath. The effects of current density, in the range of 1–9 A dm^?2, on the particle reinforcement, phase/microstructure, microhardness, and wear properties of the coating have been studied. The coatings codeposited with current density of 5 A dm^?2 at 333 Hz pulse frequency and 33% duty cycle exhibited microhardness comparable to hard chromium coatings.     

Processing and properties of copper-coated carbon fibre reinforced aluminium alloy composites

Aluminium alloy matrix composites with carbon fibre reinforcement were prepared by stir casting method. In order to avoid any interfacial reactions in the carbon fibre reinforced composites, the carbon fibres were coated with copper. The fibres were coated by electroless coating method and then characterized. Composites containing different amounts of carbon fibres were prepared by stir casting and then subjected to age-hardening treatment. Fibre distribution was fairly uniform in the composites containing up to 4 wt% carbon fibres. Tensile strength of the composites was found to be increasing up to 4 wt% carbon fibre.     

Fabrication of high‐strength steel fibre reinforced metal matrix composites by explosive bonding and their tensile properties

Summary

Steel fibre reinforced metal matrix composites (FRM) consisting of high‐strength ductile steel wire and aluminium or titanium foil were fabricated by explosive bonding. The strength properties were evaluated by tensile tests. The optimum explosive loading (explosive mass/driver plate mass) increases with the volume fraction of fibre. For the aluminium matrix composites, the micrographs obtained show sound bonding between the adjoining foils and non‐bonding between the foil and steel wire. The tensile strength of the aluminium matrix composites is 80% of the value predicted by the rule of mixtures. For the titanium matrix composites, the micrographs obtained show both bonded and unbonded regions between the adjoining foils or between the foil and steel wire. The tensile strength of the titanium matrix composites agrees with the value predicted by the rule of mixtures.     

Effects of vanadium and titanium on mechanical properties of low carbon as cast microalloyed steels

Abstract

Tensile, hardness and room temperature Charpy V notch impact tests were conducted to evaluate the variations in the mechanical properties of a low carbon cast steel containing vanadium and combinations of vanadium and titanium in the as cast condition. Tensile and hardness test results indicated that good combinations of strength and ductility can be achieved by microalloying additions. The effect of titanium on the yield strength and hardness, however, strongly depended on Ti/N ratio. Ti in hyperstoichiometric amounts increased the yield strength and hardness whereas in hypostoichiometric amounts, it did not have a considerable effect on those properties. Scanning electron microscopy and optical microscopy studies revealed that coarse TiN particles were responsible for this behaviour. On the other hand, microalloying additions significantly decreased the room temperature impact energy and led to the dominance of cleavage facets on the fracture surfaces. Although coarse TiN particles were identified to act as cleavage nucleation sites in the Ti bearing heats, no distinct microstructural feature could be identified as cleavage initiators in the microstructure of the alloy containing only vanadium.     

Cast-Bonding—a New Process for manufacturing Composite Wear Products

Abstract

A new process for producing composite products, consisting of a wear—or corrosion-resistant cladding alloy on a wrought steel substrate, is described. The cast-bonding process enables steel components of a wide range of geometries to be protected with heavy overlays of, for example, alloy white cast iron or cobalt-base material. Typical products include internally-clad pipe bends and fittings, composite valve seats and composite billet shear blades. The bond between the two materials forms primarily in the solid-state by diffusions processes following casting of the cladding alloy on to the preheated surface of the substrate. Apart from a very narrow band adjacent to the bond line, there is no dilution of the overlay material. Some degradation of the impact toughness of the substrate steel takes place in the near- bond regions on account of grain growth caused by the thermal cycle to which the steel is subjected during the cast-bonding process. The grain size is effectively refined however, and the impact properties are recovered, by a subsequent normalising treatment which also hardens alloy white cast iron overlays. Shear tests reveal that the strength of the bond is greater than that of the alloy white iron cladding, thereby giving confidence in the integrity of cast-bonded products.     

Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Abstract

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile–shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile–shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.     

Effect of electromagnetic casting process on microstructure and properties of AZ31 magnesium alloy

ABSTRACT

In this paper, AZ31 magnesium alloy is cast by applying the semi-continuous casting process with a low-frequency electromagnetic field. By studying the influence of electromagnetic field frequency, excitation current intensity and casting velocity on the microstructure and mechanical properties, the optimum process under oil-slip electromagnetic casting conditions was determined to improve the degree of grain refinement, yield strength, elongation and tensile strength of AZ31 alloy. An improved microstructure refining effect and higher hardness can be obtained with a current intensity af 60 A. The microstructures and mechanical properties obtained for different casting velocities of V = 200 mm/min and V = 230 mm/min at processing parameters of f = 30 Hz and I = 120 A were compared. Our results suggest that a higher casting speed does not lead to grain refinement or improved mechanical properties. Frequency     

Comparison of mechanical properties of die cast aluminium alloys: cold v. hot chamber die casting and high v. low speed filling die casting

Abstract

In this paper, the mechanical properties of die cast aluminium alloys made by various die casting technologies were examined. To create high quality aluminium alloy die castings, two die casting processing technologies were employed. These were (a) ultra slow speed filling cold chamber die casting and (b) high speed hot chamber die casting. Significant improvements of the fatigue and mechanical properties were obtained for both die casting systems compared to the normal high speed cold chamber die casting technique. By comparing ultra slow die casting with hot chamber die casting, it was found that the fatigue and mechanical strengths from hot chamber die casting were higher than those for ultra slow filling die casting. The differences in material strength were attributed directly to the material properties, e.g. microstructural morphology and internal defects. Spherical fine dendritic cells in the hot chamber die casting sample gave rise to high fatigue crack growth resistance; the low crack growth resistance for cold chamber die cast aluminium is mostly due to the growth of aluminium rich α phase and the presence of eutectic silicon fibres. The fatigue strength was also related to the number of internal defects, e.g. the lower the defect rate on the fracture surface, the higher the fatigue resistance and mechanical strength. The characteristics of the principal internal defect were different depending on the die casting technology: this showed fine porosity for hot chamber die casting but solidification shrinkage and the scattered chill structure for slow and high speed cold chamber die castings. The reasons for the change of material strength were therefore influenced by the die casting process.     

Influence of pulse impact on properties of liquid phase pulse impact diffusion welding SiCp/AlSi7Mg and its welding mechanism

Abstract

The influence of pulse impact on the microstructure and properties of welded joints of aluminium matrix composite SiC_p/AlSi7Mg by liquid phase pulse impact diffusion welding (LPPIDW) and its welding mechanism had been studied. It showed that during LPPIDW, under the effect of pulse impact, the interface state between SiC particle and matrix was prominent, the initial pernicious contact state of reinforcement particles had been changed from reinforcement (SiC)/reinforcement (SiC) to reinforcement (SiC)/matrix/reinforcement (SiC), and the harmful microstructure or brittle phase was restrained from the welded joint. Moreover, the density of dislocation in the matrix neighbouring to and away from the interface was higher than that of its parent composite and the dislocation entwisted each other intensively. Furthermore, the deformation mainly occurred in the matrix grain and the matrices around SiC particles engendering intensive aberration offered a high density nucleus area for matrix crystal in favour of forming nanograins, which improved the properties of welded joints distinctly, resulting in welding the composite successfully. Consequently, the tensile strength of the welded joints was up to 179 MPa, which was ～74˙6% of the strength of SiC_p/AlSi7Mg (as stir cast), and its corresponding radial deformation was less than 3%, suitable for the demand of deformation of welded specimens.     

Influence of temper condition on microstructure and mechanical properties of semisolid metal processed Al–Si–Mg alloy A356

Abstract

The microstructures and mechanical properties of strontium modified semisolid metal high pressure die cast A356 alloy are presented. The alloy A356-F (as cast) has a globular primary grain structure containing a fine eutectic. Solution treatment results in spheroidisation of the eutectic silicon particles under the T4 and T6 temper conditions. The A356-T5 maintains the fibrous silicon morphology after artificial aging. A356-T4 has better ductility and impact strength than A356-T5 due to its spheroidised silicon morphology. The impact properties of semisolid metal high pressure die cast A356 are controlled mainly by the silicon morphology and alloy strength (hardness), whereas tensile strength is determined by the degree of solid solution coupled with precipitate formation during aging.     

Control of graphite formation in solidification of white cast iron

Abstract

Graphite formation should be strictly suppressed for the most abrasion resistant white cast irons, since austenite (γ)+graphite eutectic structure shows lower hardness and selectively wears thus deteriorates the abrasion resistance even though the austenite transform to hard phase such as martensite. On the other hand, a small amount of fine graphite is desired to distribute in rolls for hot steel mills to suppress the scoring. However, strong carbide formers such as Cr, V, Nb have been increasingly added to rolls, in order to crystallise more harder carbides. As γ+carbide eutectic grows, the residual liquid among eutectic cells becomes poor in carbide formers and rich in elements which promote graphite formation. Therefore an appropriate alloy design is essential for the hot steel milling rolls. In this study, the graphite formation mechanisms are discussed for chromium cast iron, high speed steel type cast iron and Ni hard type cast iron.     

Back Matter

Abstract

This paper is concerned with the experimental determination of thermomechanical properties of a cold box sand, which have a strong influence during the solidification in a sand casting process. To this end, the uniaxial behaviour for different temperatures up to the casting temperature of an aluminium alloy is investigated. For the tests at room temperature, the authors use optical measurement equipment, which is ideally suited to measure inhomogeneous deformations and strains within the material specimens. Furthermore, different strain rates are applied to analyse rate dependent behaviour. The storage time of the sand is also varied, since it influences the material characteristic of the binder in the cold box. An effective heating procedure is developed to characterise the mechanical material behaviour due to different isothermal loadings. The pressure dependence of multiaxial stress states is investigated in a pressure cell. The experimental data are intended to develop and identify a material model for sand, taking into account the strength–differential effect (S–D effect), rate and temperature dependence and the effect of hydrostatic stress states.     

Special features of the winding bend test

Summary

This paper deals with the resistance spot weldability of steel to aluminium alloy using an intermediate layer of aluminium clad steel. Five types of clad sheet with various steel/aluminium thickness ratios were produced by hot rolling. The mechanical properties of the clad sheet changed with the thickness ratio and ranged between those of steel and:those of aluminium sheet. The peel strength of the steel/aluminium interfaces was greater than 25 N/mm.

Materials used in spot welding were 0.8 mm thick EDDQ steel sheet, three types of 1.0 mm thick aluminium alloy sheet and the clad sheet mentioned above. Spot‐weldability, including suitable welding current, nugget diameter, tensile shear strength and thickness of the intermetallic compound layer formed at the interface of the clad sheets, changed with the thickness ratio of the clad sheet. From these results, it was concluded that spot‐weldability was affected by the thickness ratio of the clad sheets.

Spot‐weldability was also affected by the alloying elements in the aluminium alloy sheet. Tensile shear strength and nugget diameter varied in various types of aluminium alloy sheet.     

Interface electrochemical corrosion behaviour of alclad Al–Zn–Mg–Cu–Cr Al alloy adhesively bonded with carbon fibre reinforced plastic stiffener

Abstract

Stiffening of Al alloy aircraft structures with carbon fibre reinforced plastic laminate called ‘patches’ is considered as a viable option to enhance fatigue life. Interface so created between the reinforcement and Al alloy structure is potential site for crevice corrosion attack. Therefore, studies were conducted to investigate the interface corrosion behaviour of peak and two-step aged Al–Zn–Mg–Cu–Cr alclad alloy with and without the patch and examine the possibility to control the interfacial attack with the addition of cerium chloride inhibitor exposed to 3·5 wt-% NaCl solution for the durations of 2 and 168 h. Electrochemical impedance spectroscopy revealed that the interface attack was significantly reduced by the addition of 1000 ppm cerium chloride. The response of the peak and two-step aged alloy for such an addition was further investigated and found that the alloy under step aged condition behaves better than that of the peak aged condition.