Fabrication and characterisation of Al–7Si–0.35Mg/fly ash metal matrix composites processed by different stir casting routes

Loose beds of hollow fly ash particles (cenospheres) were pressure infiltrated with A356 alloy melt to fabricate metal-matrix syntactic foam, using applied pressure up to 275 kPa. The volume fractions of cenospheres in the composites were in the range of 20–65%. The processing variables included melt temperature, gas pressure and particles size of fly ash. The effect of these processing variables on the microstructure and compressive properties of the synthesized composites is characterized. Compressive tests performed on these metal-matrix composites containing different volume fractions of hollow fly ash particles showed that their yield stress, Young's modulus, and plateau stress increase with an increase in the density. Variations in the compressive properties of the composites in the present study were compared with other foam materials.

Compressive characteristics of A356/fly ash cenosphere composites synthesized by pressure infiltration technique

Syntactic foams were fabricated by liquid metal infiltration of commercially pure and 7075 aluminum into preforms of hollow ceramic microspheres. The foams exhibited peak strengths during quasi-static compression ranging from −100 to −230 MPa, while dynamic compression loading showed a 10–30% increase in peak strength magnitude, with strain rate sensitivities similar to those of aluminum–matrix composite materials. X-ray tomographic investigation of the post-compression loaded foam microstructures revealed sharp differences in deformation modes, with the unalloyed-Al foam failing initially by matrix deformation, while the alloy–matrix foams failed more abruptly through the formation of sharp crush bands oriented at about 45° to the compression axis. These foams displayed pronounced energy-absorbing capabilities, suggesting their potential use in packaging applications or for impact protection; proper tailoring of matrix and microsphere strengths would result in optimized syntactic foam properties.

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Plasticity and Damage in Aluminum Syntactic Foams Deformed under Dynamic and Quasi-Static Conditions

Dry sliding wear of fly ash particle reinforced A356 Al composites

Many different types of advanced metal matrix composites are now available, some of which possess functional properties. Recent work on particle-reinforced, self-lubricating and self-healing metals and metal matrix nanocomposites (MMNCs) synthesized by solidification synthesis is reviewed. Particle-based MMNCs have been developed by several modern processing tools based on either solid- or liquid-phase synthesis techniques that are claimed to exhibit exciting mechanical properties including improvements of modulus, yield strength, and ultimate tensile strength. This article presents a brief and objective review of the work done over the last decade to identify the challenges and future opportunities in the area of functional nanocomposites. Increasing interest in lightweight materials has resulted in studies on hollow particle-filled metal matrix syntactic foams. Syntactic foams seem especially suitable for development with functional properties such as self-healing and self-lubrication. The metal matrix micro and nanocomposites, and syntactic foams having combinations of ultrahigh strength and wear resistance, self-lubricating, and/or self-healing properties can lead to increased energy efficiency, reliability, comfort of operation, reparability, and safety of vehicles. The focus of the present review is aluminum and magnesium matrix functional materials.

Functional Metal Matrix Composites: Self-lubricating, Self-healing, and Nanocomposites-An Outlook

Beds of nickel coated and uncoated cenosphere fly ash can be successfully infiltrated by molten aluminum under very low pressures. The density of the resultant composite is ≈1.4 and 1.2 g cm−3 respectively, compared to 2.68 g cm−3, the density for aluminum. The threshold pressure was found to be between 20.68 and 27.58 kPa for infiltration of molten pure aluminum into uncoated fly ash, and around 6.7 kPa for Ni-coated fly ash. These data were used to back calculate an effective wetting angle between molten pure aluminum and fly ash using Young’s and Washburn equations. The average value of the wetting angle calculated for uncoated fly ash is 111°. The microstructures and chemical composition of the composites made with coated and uncoated fly ash were studied using optical and scanning microscopy; they show good infiltration except for regions between contacting cenospheres. They also show transport of nickel from the bottom to the top of the sample when nickel coated particles were used.

Pressure infiltration technique for synthesis of aluminum–fly ash particulate composite

A package for an IC includes a carrier with a cavity formed on one of the major surfaces. Bumps of a semiconductor die are mated to contact pads located on the bottom of the cavity. The die is attached to the major surface of the carrier. The major surface creates a support which securely holds the chip in place with adhesive for assembly.

Henry Iksan

Papers

Pressure infiltration technique for synthesis of aluminum–fly ash particulate composite

Cavity chip package