Mechanical behaviour of rapidly solidified aluminium-silicon ribbon-polyester composites

Abstract

Metal-polymer composites have been synthesized in recent years [1-3], with a view to achieving a tailored set of properties, which are generally not obtainable in individual materials. These composites are finding a large number of applications because of their improved electrical and thermal properties [4]. Polymerbased composites are generally produced by using various combination of metals and plastics, e.g. impregnation of metal coating with plastics, plastic layers on metallic surfaces, sintering of metal powder and powdered thermoplastics, dispersion of metal powder or metallic ribbons into thermoplastics. It has been reported [5] that the use of layered composites, produced by aluminium and thermoplastic resins, particularly those having sandwich structure, is restricted not only to the finishing step but also can be used as semi-fabricated products. Applications of anodized alucobond [6] (two thin sheets of aluminium bonded to the thermoplastic core of the polyethylene) panels and decorative silhouettes for retail stores are excellent. Festtag and Bolliger [7] have suggested that the scaling layer of aluminium plastics composites can be freely chosen to suit the requirements of food and drug packaging. Rheological behaviour [8-10] and the dynamic and static mechanical properties [11-16] of the epoxy/ metal composites were studied by several researchers. Nicodemo and Nicolais [17] have studied the elastic moduli, stress and strain at break for styreneacrylonitrile polymer (SAN) filled with iron and aluminium powders. They have observed poor adhesion in iron/SAN composites and no adhesion in aluminium/SAN composites. Ceramic reinforcements [18] such as boron and silicon carbide or glass generally offer optimum performance on a specific property, but the "size effect" problem associated with the brittle materials limited their use. To circumvent the above problem, it has been proposed to use metals such as steel and aluminium in ribbon form [19-22] as the reinforcement in resin materials. Strife and Prewo [18] have studied the mechanical properties of composite made out of high-strength Metglass alloy 2826 MB ribbon as the reinforcement with an epoxy-nylon adhesive, FM-1000, as matrix. They have reported that the above combination of constituents with dissimilar characteristics can produce an increase in axial and transverse tensile strength and elastic modulus. In the present letter it is proposed to reinforce rapidly solidified aluminium silicon, LM 13, alloy ribbon in polymer matrix in order to produce highperformance materials. Composites of various volume fractions of rapidly solidified ribbon with polyester matrix have been produced and the ultimate tensile strength of the composites were determined. Theoretical predictions of ultimate tensile strength (UTS) of the above composites with various volume fractions of metallic ribbons compare with the experimental data. Fracture surfaces of the composites were studied in the scanning electron microscope in order to observe the interfacial bonding between the metallic ribbon and the polymeric matrix. Aluminium-silicon, LM 13, alloy (nominally contains 11 to 13wt% Si lwt% C u l w t % Mg1.5 wt % Ni-0.8 wt % Fe-0.5 wt % Mn and the rest is aluminium) is of interest because it exhibits high strength and a low coefficient of thermal expansion. LM 13 alloy melt was rapidly quenched in the form of ribbon of 160 to 200#m thick and 3mm wide. Ribbons were cast continuously at one production run using a single roll melt spinning technique. Polyester resin was mixed with 1% accelerator and 1% hardener in a beaker. Accelerator, hardner and the resin were obtained from M. P. Polymers, Bhopal, India. Ribbons were kept in layer form one over another for increasing weight fraction in the casting mould (ASTM). After 24h resin setting, specimens were removed from the mould. These were heat set for 2 h at 80°C in an oven. The ultimate tensile strengths of the composites have been measured using an Instron machine. The fractured surfaces of the composites were coated with silver metal to avoid the "charging effect", and were observed in the scanning electron microscope. Fig. 1 shows the microstructure of as-received rapidly solidified LM 13, alloy ribbon, as observed