K. Onel

The mechanical response of Al–Si–Mg/SiCp composite: influence of porosity

Abstract The effect of porosity on the mechanical and fracture behaviour in Al–Si matrix alloy and composites reinforced with SiC particles of 10 and 20 vol.% in the as-cast state and after extrusion process has been studied. Matrix alloy and composites were fabricated by compocasting and extrusion. Samples were characterized by optical microscopy, image analyzer, scanning electron microscopy and tensile tests. The results demonstrate that hot extrusion considerably reduces the porosity, while size and distribution of the reinforcement particles are also affected. In the point of fracture behaviour, the existence of large porosity is more effective.

The effect of forging on the properties of particulate-SiC-reinforced aluminium-alloy composites

Abstract Composites of an aluminium–silicon alloy (Al–5%Si–0.2%Mg) containing different volume fractions of particulate silicon carbide reinforcement and unreinforced matrix alloy samples were produced by the permanent die casting technique. The cast ingots were cut into blanks to be forged in two steps to obtain rectangular plate-shaped samples. At each step of closed-die hot forging approximately 50% reduction in thickness was obtained. The microstructures and mechanical properties of the matrix alloy and the composite samples were investigated in the as-cast state and after the forging operation. The forged microstructures had a more uniform distribution of the SiC particles and the eutectic silicon in comparison to the as-cast microstructures. Evaluation of the mechanical properties showed that the forged samples had strength values superior to those of the as-cast counterparts. After forging, the yield strength of the matrix alloy and composite samples was increased by about 80%, and the improvement in tensile strength was about 40%.The addition of increasing amounts of particulate SiC decreased the ductility and increased the yield and tensile strength up to an optimum reinforcement volume fraction over which a decrease in strength and ductility was obtained.

Microstructures and age hardenability of AL-5%si-0.2%Mg based composites reinforced with particulate SiC

Abstract Composites of an Al-0.5%Si-0.2%Mg alloy reinforced with paniculate SiC have been produced by the compocasting route. The silicon carbide was oxidized at 900 °C for 2 h and mixed into the semi-liquid alloy by means of a special stirrer. The slurry was held at 750 °C for 5 min and cast into a permanent die preheated to different temperatures and composite ingots containing 9, 13, 17, 22, and 26 vol.% SiC were obtained. The distribution of SiC particles, the porosity content and the dendrite arm spacing of the composites were determined. The phases other than the matrix and the reinforcement were identified to be Mg 2 Si, MgAl 2 O 4 and FeSi 3 Al 9 . It was found that the oxidation of SiC and the presence of magnesium in the matrix alloy rendered easy incorporation without causing any significant magnesium depletion in the matrix. It was found that the composites produced were age hardenable. After prolonged exposure to temperatures above 500 °C in the solid state, no formation of additional phases was found to take place in the microstructures.

The production of AlSi alloy-SiCp composites via compocasting: some microstructural aspects

Abstract Aluminium silicon alloy (Al-5%Si-0.2%Mg) based composites containing different volume fractions of reinforcing SiC particles are produced using the compocasting route. The particles of SiC were incorporated by a special stirrer and the slurry was poured into a permanent die of certain dimensions, preheated to various temperatures, in order to obtain different cooling rates during the solidification of the composite ingots. The microstructural characteristics such as dendrite arm spacing, SiC particle distribution, porosity and phases present in the microstructures of the composites were investigated by using light microscope, scanning electron microscope with microprobe attachment and X-ray diffractometer. High incorporation levels were obtained by using reasonably short mixing times. The ingots cast into moulds having temperatures of 80°C and below showed homogeneous SiC particle distribution. The samples with SiC volume fraction lower than 17% contained little porosity, and no formation of harmful Al4C3 was observed in any of the samples produced.

High temperature behaviour of H13 steel

Abstract In this study, an investigation was carried out in order to determine the effect of annealing temperature on the mechanical properties of H13 steel. Heat treatments were applied on samples at different temperatures in both, the as-received and as-quenched conditions. In order to indicate the effect of heat treatment temperature, hardness measurements and tensile tests were performed at all chosen temperatures. At relatively high temperatures the mechanical properties of the H13 steel have been diminished considerably.

Microwave Assisted Reaction Sintering of ZrSiO4/α -Al2O3 Mixtures

Mullite- zirconia composites have better mechanical properties than monolithic mullite ceramics and can be produced by reaction sintering of ZrSiO4 and  -Al2O3. The samples were prepared from high-purity (99.9%) α-alumina and fine zircon (ZrO2>65 wt.%) powders using PVA as binder. The powder mixtures were compacted under 80 MPa as coin shaped samples by uniaxial dry pressing and then sintered in a multimode microwave field of 2.45 GHz. The microwave effect on ZrSiO4 dissociation and mullite formation was evaluated by comparing the microwave sintered samples with those sintered conventionally. The as-reacted compacts were characterized by X-ray diffraction and scanning electron microscopy (SEM). The effects of sintering parameters on mullitization and mullite grain growth were investigated.