Grain refinement of Al–Zn–Mg alloy during equal channel angular pressing (ECAP)

Locally produced Al–Zn–Mg alloy was subjected to severe plastic deformation through Equal Channel Angular Pressing (ECAP) technique at temperatures of 150 °C and 200 °C. Rectangular thick-walled medium carbon steel die (σc = 450Mpa, σy = 176Mpa) with an L-shaped channel of uniform configuration to provide the pressing chamber was used. Four ECAP passes were imposed consecutively on set of samples for 150 °C and 200 °C temperatures, and characterized with optical microscopy, scanning electron microscopy (SEM) and x-ray diffraction (XRD). The phases were identified by X-ray diffraction (XRD) using monochromatic Cu Kα radiation, while vickers’ microhardness and tensile tests were performed for mechanical properties examination. Optical micrographs showed no tangible precipitation in the as cast samples with reduced grain width and deformation bands but at high temperatures of 150 °C and 200 °C, precipitation was promoted as a result of slipping systems activation. SEM images of the as-cast alloy exhibits dendrites of 250 ± 20 μm in size with η′ phase (MgZn2) precipitates in the inter-dendritic regions. For 150 °C ECAP temperature, a significant refinement was achieved as the passes increased with sub-grain development within the boundary and the precipitate observed has a grain size of 35 ± 15 μm, 25 ± 10 μm, 15 ± 8 μm and 8 ± 6 μm for first, second, third and fourth passes respectively. However, grain sizes of 85 ± 15 μm, 50 ± 10 μm, 30 ± 8 μm and 10 ± 5 μm for first, second, third and fourth passes were observed for 200 °C ECAP temperature. XRD results showed peaks for aluminum and other phases in as-cast condition with precipitates growth in the alloy after the first pass, identified as metastable η′ phase. As the number of ECAP passes increases, η′ peaks moved towards the equilibrium η phase confirming the transformation of η′ phase to stable η phase. The microhardness, Ultimate tensile strength (UTS) and the yield strength of Al–Zn–Mg alloy in different conditions of 150 °C and 200 °C respectively also increased with increase in the number of ECAP passes. This is due to increase in dislocation density, work hardening and grain refinement during ECAP process

PHYSICAL PROPERTIES OF ULTRAFINE CLAY-WOOD DUST HYBRID REINFORCED RECYCLED POLYETHYLENE TEREPHTHALATE MATRIX COMPOSITE FOR SEMI-STRUCTURAL APPLICATIONS

This research involves the production of polymer matrix composites as a combination of ultrafine clay, wood dust and recycled Polyethylene Terephthalate (PET) where the matrix is recycled Polyethylene Terephthalate, and the dispersed phase (hybrid fillers) are ultrafine clay and wood dust. The proportion of recycled PET used for composite production varied from 97 wt% - 99 wt%, while that of wood dust varied from 0.5 wt% - 2 wt% and ultrafine clay from 0.5 wt% - 2 wt%. Physical tests including porosity, water absorption and flammability tests were also carried out on the developed samples. Results obtained from physical tests revealed that the densities of ultrafine clay-wood dust hybrid reinforced recycled PET composites (1.051 - 1.209 g/cm3) were relatively higher than those of ultrafine clay reinforced recycled PET composites and wood dust reinforced recycled PET composite. The WD2 composite sample has the least experimental density value of 0.793 g/cm3. The percentage water absorption rate of the wood dust reinforced recycled PET composites were relatively higher than the ultrafine clay reinforced recycled PET composites. The percentage water absorption rate of the hybrid reinforced recycled PET composites were in between those of the wood dust reinforced and ultrafine clay reinforced fillers. The UFC0.5 composite sample (0.5 wt% ultrafine clay, 0 wt% wood dust reinforced 99.5 wt% recycled PET composite sample) has the least percentage water absorption value of 0.12846535 when compared to other samples. The porosity of the hybrid reinforced recycled PET composite samples were relatively lower than the control sample and separately reinforced samples with ultrafine clay and wood dust. However, HB1 composite sample has the least % porosity value of 1.1563. UFC2 has the least flame propagation rate of value of 0.05482456 mm/s. Keywords: Ultrafine Clay, Recycled Polyethylene Terephthalate, Polymer Matrix Composite, Wood Dust