Microstructure,tensile properties and fracture behaviour of aluminium alloy 7150

A study has been made to understand the microstructure, tensile properties and fracture characteristics of aluminium alloy 7150. Detailed optical and transmission electron microscopical observations were used to analyse the intrinsic microstructural features of the alloy in the T77 condition. The alloy was deformed to failure over a range of strain rates in environments of 3.5% sodium chloride solution and laboratory air. The environment was found to have little influence on strength of the alloy. The strength only marginally increased with an increase in strain rate. However, for all strain rates, the ductility of the alloy degraded in the aggressive environment. The ratio of strain to failure in sodium chloride solution to that in laboratory air indicates that the alloy is only mildly susceptible to stress corrosion cracking. The fracture behaviour was different in the two environments. However, in a given environment the fracture behaviour was essentially the same. In the aggressive environment fracture was predominantly intergranular while fracture revealed a ductile transgranular failure in laboratory air. An attempt is made to discuss the kinetics of the fracture process in terms of competing mechanistic effects involving intrinsic microstructural features, matrix deformation characteristics, environment and strain rate.     

Influence of aging condition on tensile and fatigue fracture behaviour of aluminium alloy 6063

Abstract

An Al–Mg–Si alloy 6063 was heat treated in the underaged, peak aged, and overaged conditions. The microstructures of the alloy in the different aging conditions were examined using transmission electron microscopy. Tensile and fatigue tests were carried out and the resulting fractures were studied using scanning electron microscopy. It has been found that the alloy shows different tensile and fatigue properties and different modes of fracture under different aging conditions. The results have been explained in terms of slip distribution and grain boundary strength.

MST/1188     

Microstructure, tensile deformation and fracture behaviour of aluminium alloy 7055

The microstructure, tensile deformation and fracture behaviour of aluminium alloy 7055 were studied. Detailed optical and electron microscopy observations were made to analyse the as-received microstructure of the alloy. Detailed transmission electron microscopy observations revealed the principal strengthening precipitates to be the hexagonal disc-shaped η′ phase of size 2 mm×20 mm and fully coherent with the aluminium alloy matrix, the presence of spheroidal dispersoids, equilibrium grain-boundary η precipitates and narrow precipitate-free zones adjacent to grain-boundary regions. It is shown that microstructural characteristics have a profound influence on tensile deformation and fracture behaviour. Tensile test results reveal the alloy to have uniform strength and ductility in the longitudinal and transverse orientations. Strength marginally decreased with an increase in test temperature but with a concomitant improvement in elongation and reduction in area. No change in macroscopic fracture mode was observed with sample orientation. Fracture, on a microscopic scale, was predominantly ductile comprising microvoid nucleation, growth and coalescence. The tensile deformation and fracture process are discussed in the light of the competing influences of intrinsic microstructural effects, matrix deformation characteristics, test temperature and grain-boundary failure. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructure,tensile properties and fracture behaviour of an Al-Cu-Li-Mg-Zr alloy 8090

The addition of lithium to aluminium alloys has the potential for providing a class of high strength alloys with exceptional properties suitable for aerospace applications. One such candidate is 8090, a precipitation hardenable Al-Li-Cu-Mg alloy. Detailed optical microscopical observations were used to analyse the intrinsic microstructural features of the alloy. It is shown that microstructural characteristics have a pronounced influence on tensile properties and fracture behaviour of the alloy in the peak-aged, maximum strength condition. Tensile test results indicate that the alloy has property combinations comparable with other high strength commercial aluminium alloys. The elongation and reduction in area are higher in the transverse direction of the extruded plate. A change in fracture mode was observed with direction of testing. We rationalize such behaviour based on the grain structure of the material, and the nature, distribution and morphology of the second-phase particles. An attempt is made to discuss the kinetics of the fracture process in terms of several competing mechanistic effects involving intrinsic microstructural features, deformation characteristics of the matrix, brittleness of the grain boundary precipitates and grain boundary failure. The role of stress on particle fracture is highlighted.     

Microstructure,tensile properties and fracture behaviour of an Al-Cu-Mg alloy 2124

The microstructure, tensile properties and fracture behaviour of aluminium alloy 2124 were studied. Detailed optical and electron microscopical observations were made to analyse the as-received microstructure of the alloy. It is shown that microstructural characteristics have a profound influence on tensile properties and quasi-static fracture behaviour of the alloy. Tensile test results indicate that the alloy has uniform strength and ductility in the longitudinal and transverse orientations. The elongation and reduction in area are higher in the transverse direction of the extruded plate. No change in fracture mode was observed with direction of testing. Fracture, on a microscopic scale, was ductile, comprising of void nucleation, growth and coalescence. The fracture process is discussed in terms of competing influences of intrinsic microstructural features, deformation characteristics of the matrix and grain-boundary failure.     

Influence of heat treatment processes on fatigue performance of particle reinforced aluminium alloys

Abstract

The fatigue performance of particle reinforced metal matrix composites improves as the matrix strength is increased. However, the heat treatment required for high matrix strength induces residual stresses into the material, which need to be balanced against potential distortion during machining of components. This paper reports results showing the fatigue behaviour of a 2124 aluminium alloy reinforced with 25 vol.-% of silicon carbide particles. The effect of quench medium on tensile and rotating bend fatigue strength is reported. Results are correlated with residual stress profiles measured in quenched plates of the material.     

Effect of interfacial reaction on fracture behaviour of aluminium borate whisker reinforced aluminium composite

Abstract

An aluminium borate whisker reinforced aluminium composite with a whisker volume fraction of 25% was fabricated by the squeeze casting method. The tensile and impact fracture behaviours of the composite were studied. Observation via TEM indicated that the higher the casting temperature, the higher the degree of interfacial reaction. Tensile and impact experiments showed that there is an optimum degree of interfacial reaction corresponding to the maximum strength and toughness of the composite. Observation of the fracture surfaces of the composites using SEM suggests that the interfacial reaction plays an important role in the fracture mechanism of the composite.     

Wear behaviour of an aluminium matrix composite

The wear behaviour of a composite material consisting in AS12UNG alloy reinforced with 15% short fibres of alumina has been studied. The material composition and the wear test conditions were defined in order to evaluate the potential performance of automotive pistons produced with such composite composition. As initially expected, the results indicate that an increase in the sliding velocity lead to higher wear rates in the stationary stages, and higher applied loads also induced acceleration in the wear process. Also, reciprocating sliding movement is clearly more damaging than the circular. However, results have shown that wear rates at 150 °C are lower than those recorded at room temperature representing a promising result for the use of this material in components that operate in this condition. This advantageous behaviour is lost at temperatures near to 300 °C, when a marked increase in the wear rate and a signification contribution of adhesive wear were observed.     

Influence of heat treatment and hot working on fracture toughness of cast aluminium base composites

Abstract

Evaluation of toughness in terms of the fracture energy E*, obtained using Charpy impact testing and the fracture toughness K_Ic obtained from bend tested specimens, has been carried out for various cast particle reinforced aluminium base composites, namely, A356–SiC, A357–SiC, 6061–Al₂O₃, and 2014–Al₂O₃. In practice, the first two are used in the as cast foundry condition and the last two in the cast and extruded condition. Hot extrusion or rolling to reduction ratios between 2 : 1 and 50: 1 was conducted on the 6061 and 2014 composites to characterise the influence of working processes. Heat treatment conditions considered included the as cast (or as worked), solid solution treated, and T6 temper. The results show that extrusion or rolling can markedly improve the toughness, but on thermal aging the toughness is reduced. The increase in total fracture energy by hot working is mainly caused by the increase of initiation energy, whereas the decrease of fracture energy by artificial aging is controlled by the propagation energy. The values of K_Ic obtained for these composites are from 15 to 25 MN m^?3/2. Comparisons and interpretations of the dynamic Charpy fracture energy, quasistatic fracture toughness, and fracture surface of the four composites are also presented.

MST/1806     

Microstructure,tensile properties and fracture behaviour of Al2O3 particulate-reinforced aluminium alloy metal matrix composites

The tensile deformation and fracture behaviour of aluminium alloy 2014 discontinuously-reinforced with particulates of Al₂O₃ was studied with the primary objective of understanding the influence of reinforcement content on composite microstructure, tensile properties and quasi-static fracture behaviour. Results reveal that elastic modulus and strength of the metal-matrix composite increased with reinforcement content in the metal matrix. With increase in test temperature the elastic modulus showed a marginal decrease while the ductility exhibited significant improvement. The improved strength of the Al-Al₂O₃ composite is ascribed to the concurrent and mutually interactive influences of residual stresses generated due to intrinsic differences in thermal expansion coefficients between constituents of the composite, constrained plastic flow and triaxiality in the soft and ductile aluminium alloy matrix due to the presence of hard and brittle particulate reinforcements. Fracture on a microscopic scale initiated by cracking of the individual or agglomerates of Al₂O₃ particulates in the metal matrix and decohesion at the matrix-particle interfaces. Failure through cracking and decohesion at the interfaces increased with reinforcement content in the matrix. The kinetics of the fracture process is discussed in terms of applied far-field stress and intrinsic composite microstructural effects.     

Effect of solution heat treatment and additives on the hardness, tensile properties and fracture behaviour of Al-Si (A413.1) automotive alloys

A study was carried out to determine the role of Mg, Cu, Be, Ag, Ni, and Zn additives during the solution heat treatment of grain refined, Sr-modified eutectic A413.1 (Al-11.7% Si) alloy, and their consequent effect on mechanical properties. For comparison purposes, some of the alloys were also studied in the non-modified condition. The alloys were cast in the form of test bars using a steel permanent mold preheated at 425°C that provided a microstructure with an average dendrite arm spacing (DAS) of 22 m. The test bars were solution heat treated at 500 ± 2°C for times up to 24 h, followed by artificial aging at 155°C for 5 h (T6 treatment). Tensile and hardness tests were carried out on the heat-treated test bars. Details of the microstructural evaluation are reported in a previous article [1].With respect to the mechanical properties, it is found that the hardness and strength (YS, UTS) of Mg-containing alloys decrease with the addition of Sr due to the sluggish dissolution of the Al₅Cu₂Mg₈Si₆ phase during solution treatment, and a delay in the precipitation of Mg₂Si or Al₂MgCu phases during artificial aging thereafter. The properties of the Cu-containing alloys, however, remain unaffected by the addition of Sr. With the exception of Ni, all alloying elements used improve hardness and strength, particularly after heat treatment. In the case of Ni, addition of up to 1.41% Ni is observed to decrease the mechanical properties in the T6 condition.Fracture of non-modified alloys takes place through crack initiation within the brittle acicular Si particles without the crack passing through the ductile Al matrix. In the Sr-modified alloys, the fracture is of ductile type, as evidenced by the pinpoint nature of the -Al dendrites on the fracture surface. The number of cracked Si particles and intermetallics beneath the fracture surface increases in proportion to the increase in alloy strength.     

Predicting fracture from the tensile properties of a composite biomaterial

Fracture and tensile tests were conducted on a composite biomaterial consisting of polycarbonate matrix and calcium phosphate fibers. The fibers were short and randomly oriented. Test results were compared for composites with and without a surface treatment of the fibers.

A nonlinear finite element method was used to predict the maximum loads on pre-cracked panels. The method used the unnotched stress–strain behavior to predict the failure process in notched panels. A cohesive stress zone near the crack tip was used to model damage, stable crack growth, and failure. As in the experiments, the predicted loads were lower for the composite with coated fibers. For both materials, the predicted maximum loads were within the 6% of the experimental loads.     

Influence of thermomechanical ageing on tensile properties of 2014 aluminium alloy

2014 aluminium alloy was subjected to various thermomechanical ageing (TMA) treatments which included partial peak ageing (25% and 50%), warm rolling (10% and 20%) and further ageing to peak hardness level at 160 ° C. The tensile tests reveal that TMA treatments cause a substantial improvement in tensile properties and thermal stability. The electron microscopic studies reveal that the TMA treatments affect substantially the ageing characteristics. The TMA Ib treatment yields the finest needles having longitudinal dimensions of 40nm. The TMA treatments also lead to precipitate-dislocation networks of different densities. It is observed that TMA IIb treatment results in the densest precipitate-dislocation tangles of all the TMA treatments. As a result, a significant improvement in the tensile properties of 2014 aluminium alloy has been observed.     

Effect of thermal ageing on hardness,tensile and impact properties of an alumina microsphere-reinforced aluminium metal-matrix composite

Thermal ageing studies have been carried out with an alumina microsphere-reinforced 6061 aluminium metal-metrix composite (MMC). A solution treatment temperature of 530°C for 1.5 h and ageing temperature 175°C with ageing time ranging between 0 and 12 h have been used. It was observed that the hardness achieves a peak value in about 8 h; the ultimate tensile strength shows an increase with increasing ageing time, and reaches a plateau at about 10 h. On the other hand, elongation to failure and impact properties show a sharp decline at approximately 4 h of ageing time. Also, a limited amount of experiments using 175°C/8 h ageing after solution treatment at 510, 490, 470 and 430 °C for 1.5 h show that the hardness of the MMC deceases steadily as the solution treatment temperature is decreased.     

Influence of heat treatment on microstructure and tensile properties of GlidCopR dispersion strengthened copper alloy

Dispersion strengthened copper is a family of commercial engineering alloys comprised of fine aluminum oxide particles dispersed in a pure copper matrix. In this study, the influence of heat treatment on microstructure and tensile properties of GlidCop^R dispersion strengthened copper alloy is examined. Heat treating the as-rolled alloy was found to have no appreciable influence on grain structure and intrinsic microstructural features. The strength of the material decreases with heat treatment with concomitant improvement in ductility. The material maintains a high value of yield strength retention ratio. The influence of heat treatment on tensile properties is detailed.     

Tensile properties and fracture behaviour of polypropylene-nickel-coated carbon-fibre composite

Polypropylene-based composites reinforced with nickel-coated carbon fibres have been prepared and the effect of filler content on tensile properties and fracture behaviour at different temperatures and strain rates was investigated. The elastic modulus of such composites is enhanced by two orders of magnitude while the tensile strength and strain-to-break are lowered. The fracture toughness parameters,G _c andK _c, are also enhanced with filler content. The yield stress of this composite showed strain rate and temperature dependence. Activation energy and volume of a single rate-activated yielding process, at relatively high strain rates, were determined. The variations of the measured physical quantities are discussed in terms of the observed composite morphology.On sabbatical leave from the Physics Department, University of Jordan, Amman, Jordan.     

Effect of sillimanite particle reinforcement on dry sliding wear behaviour of aluminium alloy composite

Abstract

The effect of sillimanite reinforcement on the dry sliding wear behaviour of aluminium silicon alloy (BS LM6) composite was investigated using a pin-on-disc sliding wear test machine. The composite specimens were prepared using the liquid metallurgy technique and 10 wt-% of sillimanite particles were incorporated in the matrix alloy. Sliding wear tests were conducted at applied pressures between 0.2 and 1.6 MPa and speeds of 1.89, 3.96 and 5.55 m s^-1. The matrix alloy was also prepared and tested under identical conditions in order to enable comparison. It was observed that the sillimanite reinforced composite exhibited a lower wear rate than the matrix alloy. Increase in applied load increased the wear rate while increase in speed exhibited the reverse effect. The seizure pressure of the composite was significantly higher than that of the matrix alloy. The temperature rise near the contacting surface and the coefficient of friction were less in the composite than in the matrix alloy. SEM micrographs of the worn surface and subsurface were used to predict the nature of the wear mechanism.     

Effect of heat treatment on tensile properties of friction stir welded joints of 2219-T6 aluminium alloy

Abstract

The effect of post-weld heat treatment (PWHT) on the tensile properties of friction stir welded (FSW) joints of 2219-T6 aluminium alloy was investigated. The PWHT was carried out at aging temperature of 165°C for 18 h. The mechanical properties of the joints were evaluated using tensile tests. The experimental results indicate that the PWHT significantly influences the tensile properties of the FSW joints. After the heat treatment, the tensile strength of the joints increases and the elongation at fracture of the joints decreases. The maximum tensile strength of the joints is equivalent to 89% of that of the base material. The fracture location characteristics of the heat treated joints are similar to those of the as welded joints. The defect free joints fracture in the heat affected zone on the retreating side and the joints with a void defect fracture in the weld zone on the advancing side. All of the experimental results can be explained by the hardness profiles and welding defects in the joints.     

Influence of spray atomization and deposition processing on microstructure and mechanical behaviour of an aluminium alloy metal-matrix composite

An aluminium alloy metal matrix discontinuously reinforced with silicon carbide particulates, was synthesized using the spray atomization and co-deposition technique. Microstructural characterization studies were performed to provide an understanding of the intrinsic effects of carbide particulate co-injection into the aluminium alloy metal matrix. Results reveal the ageing kinetics to be altered by the reinforcing ceramic particulates. Ambient temperature tensile tests revealed that the presence of particulate reinforcement in the aluminium alloy metal matrix degrades both strength and ductility. The results obtained are discussed in relation to thermal conditions during spray co-deposition and contributions from reinforcement to intrinsic microstructural effects and mechanical response.