Aluminum Alloy Metal Matrix Research Articles

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.

Effect of particulate silicon carbide on cyclic strain resistance and fracture behavior of X2080 aluminum alloy metal matrix composites

A study has been made to understand the low-cycle fatigue properties and fracture behavior of aluminum alloy X2080 discontinuously-reinforced with varying amounts of silicon carbide particulates. The X2080/SiC p composite specimens were cyclically deformed over a range of cyclic-strain amplitudes, using tension-compression loading under total strain amplitude control, giving fatigue failure lives of less than 10 4 cycles. The X2080/SiC p composites exhibited hardening at all cyclic plastic strain amplitudes and for the different volume fractions of the discontinuous reinforcement in the ductile metal matrix. The degree of cyclic hardening was observed to be greater at the higher cyclic strain amplitudes than at corresponding lower strain amplitudes. Micromechanisms controlling the hardening response during cyclic straining are highlighted and rationale for the observed hardening behavior is discussed. The plastic strain-fatigue life response was found to degrade with an increase in carbide particle content in the aluminum alloy matrix. The cyclic fracture behavior of the composite is discussed in light of composite microstructural effects, cyclic plastic strain amplitude and concomitant response stress.

Fracture at elevated temperatures in a particle reinforced composite

The tensile fracture behavior of a cast and extruded 2014 aluminum alloy metal matrix composite (MMC) reinforced with 10, 15, and 20 vol.% aluminum oxide particles was investigated as a function of temperature between 100 and 300°C and hold time, and compared with the unreinforced alloy. In addition, the effect of aging condition was investigated in a 15 vol.% composite tested at 200°C. At lower temperature the composites have higher yield strength and UTS than the unreinforced material, and both decrease with increasing temperature. At higher temperatures all the materials have similar strength levels. The elongation is lower in the composites, decreasing with increasing level of reinforcement and increasing with increasing temperature, except at the highest temperature where all the composites are about the same. The microstructural damage in the composites also varies with temperature: particle fracture dominates at lower temperatures and interparticle voiding is the main damage feature at elevated temperatures. The time at temperature, and hence the degree of overaging, has little effect on the observed trends in the composite, in contrast with the unreinforced material where the density of voids decreases with increasing hold times. The transition temperature where the major damage changes from particle cracking to interparticle voiding increases with volume fraction and particle size, and decreases with overaging. The cracked particle density and void density both increase with strain, and the highest rate of increase occurs in the overaged material. In general, the tendency for particle cracking is reduced and for interparticle voiding is increased by any factor which permits accomodation of strain by the matrix, such as lower volume fraction of particles, small particle size, nonclustered particle distribution, and matrix softening from underaging or overaging.

Effects of Alumina Fibre content on properties of aluminium alloy metal matrix composite: K.W. Kaczmzar and K.U. Kainer, (Technical University, Clausthal-Zellerfeld, Germany), Powder Metallurgy, Vol 35, No 2, 1992, 133–136

This paper explores the possibility of producing metal-matrix composites using the explosive compaction method. Attempts have been made to compact powders of 2124 Al and silicon carbide. The effect of the explosive pad thickness and related parameters such as the impact energy imparted to the powder and the ratio of the explosive mass to the powder mass (Em/Pm) on the density of the compacts have been studied. Microstructural variations with respect to the processing conditions have been investigated also. The compacted 2124-20 vol.% SiCp composite specimens have been subjected to hot rolling at 520°C and age hardened. The tensile properties of the composites have also been evaluated.

Effects of microstructure on the strain-controlled fatigue failure behavior of an aluminium-alloy/ceramic-particle composite

A study has been made to understand the cyclic fatigue and cyclic fracture characteristics of a cast aluminium alloy metal matrix discontinuously reinforced with particulate silicon carbide. The Al/SiC p composite was strained to failure over a range of strain amplitudes giving lives of less than 10 4 cycles to failure. The specimens were cycled by using tension-compression loading under total strain control. In the as-cast condition, the aluminum-alloy/ceramic composite displayed combinations of cyclic hardening and softening to failure at higher cyclic-strain amplitudes, and progressive softening to failure at low cyclic-strain amplitudes. The spray-atomized and deposited composite exhibited softening to failure at the higher cyclic-strain amplitudes and combinations of softening and hardening behavior at the lower strain amplitudes. The observed hardening and softening behavior is a mechanical effect and attributed to concurrent and competing influences of interactions between cyclic deformation and composite microstructure during cyclic straining. The processed microstructure exhibited better cyclic ductility and cyclic-strain resistance than the as-cast composite microstructure. The cyclic fatigue behavior of the alloy is briefly interpreted in the light of composite microstructural effects, plastic strain amplitude and concomitant response stress.

Mechanical behavior of a continuous fiber-reinforced aluminum matrix composite subjected to transverse and thermal loading

T he transverse properties of an aluminum alloy metal matrix composite reinforced by continuous alumina fibers have been investigated. The composite is subjected to both mechanical and cyclic thermal loading. The results of an experimental program indicate that the shakedown concept of structural mechanics provides a means of describing the material behavior. When the loading conditions are within the shakedown region the material finally responds in an elastic manner after initial plastic response, and for loading conditions outside the shakedown region the material exhibits a rapid incremental plastic strain accumulation. The failure strain varies by an order of magnitude according to the operating conditions. Hence for high mechanical and low thermal loading the failure strain is small, while for low mechanical and high thermal loading the failure strain is large.

Mechanical characterization and modeling of non-linear deformation and fracture of a fiber reinforced metal matrix composite

The non-linear anisotropic mechanical behavior of an aluminum alloy metal matrix composite reinforced with continuous alumina fibers has been determined experimentally. The mechanical behavior of the composite has been modeled by assuming that the composite has a periodical microstructure. The resulting unit cell problem has been solved with the finite element method. Excellent agreement was found between theoretically predicted and measured stress-strain responses for various tensile and shear loadings. The stress-strain responses for transverse and in-plane shear were found to be identical and this will provide a simplification of the constitutive equations for the composite. The composite has a very low ductility in transverse tension and a limited ductility in transverse shear that has been correlated to high hydrostatic stresses that develop in the matrix. The shape of the initial yield surface has been calculated and good agreement was found between the calculated shape and the experimentally determined shape.

Microstructure-property relationships of in situ reacted TiC/AlCu metal matrix composites

A novel technique was utilized for the fabrication of in situ titanium carbide reinforced aluminum alloy metal matrix composites. The reacted, cast, extruded and heat-treated samples exhibited a homogeneous distribution of fine (0.1–3 μm) TiC platelets in a fine-grained recrystallized Al4.5wt.%Cu matrix. Elevated temperature tensile testing indicated that the composite retains its room temperature strengths up to 250 °C and compared favorably with composites fabricated by more complex and costly processes. When compared with Al4.5wt.%Cu alloy processed similarly but without the TiC reinforcement, the additions of TiC resulted in a yield strength and tensile strength increase of 130% and 65% respectively. Fractographic analysis indicated ductile failure, although the ductility and strength were limited by the presence of coarse titanium aluminides (Al 3Ti).

Plane strain fracture toughness test procedures for particulate metal matrix composites

AbstractProcedures for plane strain fracture toughness tests on a number of particulate reinforced aluminium alloy metal matrix composites (MMCs) have been examined. Measurements of toughness are reported on a range of particulate aluminium alloy MMCs and the results are compared with validity criteria in standards for metallic materials. In particular, the effect of testpiece thickness was studied in a 6000 and a 2000 series aluminium alloy containing, respectively, 25 and 30% silicon carbide. The results are compared with other published work on the toughness of particulate reinforced MMCs.MST/1225

Plane strain fracture toughness test procedures for particulate metal matrix composites

Procedures for plane strain fracture toughness tests on a number of particulate reinforced aluminium alloy metal matrix composites (MMCs) have been examined. Measurements of toughness are reported on a range of particulate aluminium alloy MMCs and the results are compared with validity criteria in standards for metallic materials. In particular, the effect of testpiece thickness was studied in a 6000 and a 2000 series aluminium alloy containing, respectively, 25 and 30% silicon carbide. The results are compared with other published work on the toughness of particulate reinforced MMCs.MST/1225

Effects of matrix microstructure and particle distribution on fracture of an aluminum metal matrix composite

Abstract This paper presents the results of a study on the effects of matrix microstructure and particle distribution on the fracture of an aluminum alloy metal matrix composite containing 20% by volume SiC particulate. The matrix microstructure was systematically varied by heat treating to either an under- or over-aged condition of equivalent strength, and was characterized using a combination of techniques. Quantitative metallographic techniques were utilized to characterize the material with respect to size, size distribution, and particle clustering, while transmission electron microscopy was utilized to characterize the details of the matrix microstructure in addition to the effects of aging on the character of the particle/matrix interfaces. Fracture experiments were conducted on smooth tensile, notched bend, shortrod toughness, and on specimens designed to permit controlled crack propagation, in an attempt to determine the effects of matrix microstructure and clustered regions on the details of damage accumulation. Large effects of microstructure on the notched properties were obtained with little effect of microstructure on tensile ductility. It is shown that the micromechanisms of fracture are significantly affected by the details of the matrix microstructure, interface character, and degree of clustering in the material. Fracture of the SiC was predominant in the underaged materials, with a preference for failure in the matrix and near the interface in the overaged material. Metallographic and fractographic analyses revealed that clustered regions were preferred sites for damage initiation in both the aging conditions tested, while preliminary results additionally indicate that damage accumulation ahead of a propagating crack also tended to occur in clustered regions.