Hussain Zuhailawati

Cold spray deposition of hydroxyapatite powder onto magnesium substrates for biomaterial applications

A simple, modified, cold spray process was developed in which hydroxyapatite powder was coated onto pure magnesium substrates preheated to 350 or 550°C and ground to either 240 or 2000 grit surface roughness, with stand-off distances of 20 or 40 mm. The procedure was repeated five and 10 times. The hydroxyapatite coatings did not show any phase changes. Atomic force microscopy revealed a uniform coating topography, and scanning electron microscopy revealed good bonding between the coated layers and the substrates. As the p values were < 0·05, all factors except the number of sprays were considered to be significant. The response optimiser indicated that a 22·7 mm stand-off distance, a 649·2 grit surface roughness and a 496°C substrate heating temperature produced good hydroxyapatite coatings of 46·3 μm thickness, 436·5 MPa nanohardness and 43·9 GPa elastic modulus. The modified cold spray technique with substrate heating showed promising results in terms of product coating thickness and mechanical properties.

Studies on Mechanical Alloying of Copper-Tungsten Carbide Composite for Spot Welding Electrode

This article presents a study on the properties and performance of copper-based composite reinforced with recycled tungsten carbide powder as spot welding electrode. The copper-tungsten carbide composite electrode was prepared by mechanical alloying and powder forging before being machined into truncated cone-face geometry. The welding operation was conducted on galvanized steel using a pedestal-type spot welding machine. Composites with higher density and electrical conductivity were obtained after mechanical alloying for shorter time. In contrast, a higher hardness is shown in the composite, which was mechanically alloyed to longer time. The strength of the welded steel coupon was found to increase with decreasing milling time due to an increase in density and electrical conductivity. The wear behavior of the composite revealed that the deformation of the spot weld electrode increased with increasing milling time.

Mechanical Properties of Friction Stir Processed 1100 Aluminum Reinforced with Rice Husk Ash Silica at Different Rotational Speeds

This paper presents a study on friction stir processed 1100 aluminum withincorporation of rice huskash derived, amorphous silica particles and fabricated at different tool rotational speeds. During friction stirring amorphous silica powder was placed into a groove made in the joining line of Al 1100 plates. Friction stirringwas performed with clockwise tool rotational speeds of 600 rpm, 865 rpm, 1140 rpm or 1500 rpm with a constant 45 mm/min travelling speed and a 2° tilt angle. High rotational speed (1140 rpm) facilitated material flow in the stir zone, contributing to fine aluminum matrix grain size (30- 10μm) as a result of dynamic recrystallization. Stirring at this rotational speed also caused the fracturingrelated refinement of silica particles to 10μm particle sizethat isassociated with good distribution in the aluminum matrix. Reduction in wear rate of friction stir processed Al1100 with improved hardness was believed to be due to the presence of hard silicawith high interfacial strength and high hardness of recrystallized aluminum grains in the stir zone.

Microstructure Evolution of Conventional and Semi-Solid Cast of A356 Aluminium Alloy with Addition of Inoculant

This paper investigated the effect of inoculant, Al-5Ti-1B in conventional and semi-solid casting A356 aluminium alloy. A356 aluminium alloy was melted at 850 oC and poured at 680 °C directly into the steel mould and on the inclined slope into steel mould. Inoculant was added in various percentages of 1 wt.%, 2 wt.%, 3 wt.% and 3.5 wt.% in A356 aluminium alloy melt. Microstructure and microhardness were characterized using optical microscope and Vicker’s microhardness tester. The addition of master alloy up 3.5 wt.% Al-5Ti-1B in conventional casting refined dendritic structure with average grain size of 33.41 μm. The microstructures of semi-solid A356 aluminium alloy with addition of Al-5Ti-1B consist of equiaxed structure of α-Al. Further addition of Al-5Ti-1B refined the globular structure of α-Al. The higher hardness was achieved for A356 alloy prepared using semi-solid with addition of 3.5 wt.% of Al-5Ti-1B.

Cryorolling of Al 5083 Alloy: Microstructure and Mechanical Properties at Various Post Annealing Temperatures

The present work discusses the effect of post annealing at different temperatures on cryorolled Al 5083 alloy. A new method called cryorolling has been widely studied among the researchers due to its potential of obtaining ultrafine grained which contributed to the enhancement of mechanical properties of metal alloys. The samples were immersed in liquid nitrogen followed by cryorolling and then the samples were annealed at various temperatures (150 °C, 200 °C, 250 °C, 300 °C). The hardness and tensile values decreased with increasing post annealing temperatures. The microstructure also showed some coarsening of subgrains after post annealing.

Synthesis of biodegradable Mg-Zn alloy using mechanical alloying: Effect of ball to powder weight ratio

The aim of this work was to study the effect of ball to powder weight ratio (BPR) on biodegradable binary magnesium-zinc (Mg-Zn) alloy synthesized using mechanical alloying. A powder mixture of Mg-5wt%Zn was milled in a planetary mill under argon atmosphere using a stainless steel container and balls. Milling process was carried out at 200 rpm for 5 hours using various BPR (i.e. 5:1, 10:1, 15:1, 20:1). Then, as milled powder was compacted under 400 MPa and sintered in a tube furnace at 300 °C in argon flow for an hour. The sintered density and microhardness of the alloy increased as BPR increased up to 15:1. However a further increasing showed a reduction in both density and microhardness which due to enlargement of crystallite and particle which resulted from the excessive internal energy during mechanical alloying.

Dry wear behavior of cooling-slope-cast hypoeutectic aluminum alloy

Abstract This study investigated the effect of use of a cooling slope on the microstructure, hardness and wear behavior of Al-7Si-Mg alloy. The Al-7Si-Mg alloy was cast with and without a cooling slope at a pouring temperature of 640 °C. Examination with optical and electron microscopes showed that the microstructure of cast samples using the cooling slope comprised fine and globular primary α-Al phase with homogeneous distribution of eutectic phase, while conventionally cast samples featured coarse and dendritic primary α-Al phase. The wear resistance of the cast sample was significantly better with cooling slope casting. The wear mechanism was found to be a combination of adhesion, delamination, oxidation and abrasive wear for both cooling slope- and conventionally cast samples. The wear mechanisms of cast samples both with and without cooling slope are similar and follow Archards law. The cooling slope-cast samples with fine and globular α-Al phase, high hardness and low specific wear rate (K′) showed the highest wear resistance of 10.08 × 10−5 mm3 N−1 m−1.

Sic-Reinforced Aluminum-Silicon Composite via Pressureless Infiltration Using Polystyrene as External Binder for Electronic Assemblies

SiC-reinforced aluminum composite was developed by pressureless infiltration technique using polystyrene as external binder. The metal matrix composites obtained were characterized for phase composition, microstructure, density, porosity, hardness and thermal expansion. The SiC particles were uniformly distributed within the Al-Si matrix with the help of polystyrene as external binder. The variation in the density of the composites was found to be linear with volume percent of SiC. The hardness increased with increasing SiC content and highest hardness was 64.52 HV achieved with addition of 20 vol.% SiC. Thermal conductivity of the composites increased with increasing of SiC volume fraction up to 27.34 W/mK.

Design of Experiment (DOE) Study of Hydroxyapatite-Coated Magnesium by Cold Spray Deposition

In this study, hydroxyapatite powder was sprayed onto pure magnesium plate using a simple modified cold spray process. The effects of process parameters (i.e.standoff distance, surface roughness, substrate, substrate heating temperature and number of spray) were studied using 2k-1 factorial design.Analysis of variant (ANOVA) were used to determine the significant of process parameters on the coating. Thickness of coating, nanohardness and elastic modulus were chosen as the responses for assessing the most significant parameters that affected the hydroxyapatite coated onto pure magnesium plate. HAP particles have found to be bonded well in sample of run 11 while sample of run 4 show poor bonding between HAP particles and magnesium substrate. The effect of individual variables on the response was briefly discussed.

The Role of Roller Speed on Solidification of Al-Mg-Si Alloy during Twin Roll Strip Casting

In the production of aluminum alloy strips for packaging industry twin roll strip casting technique is now being extensively employed. The twin roll caster has advantage of the energy saving, low cost equipment and rapid solidification. The present research aimed to investigate the microstructure and hardness of twin roll strip cast aluminum alloys strips by varying the speed of roller cast. Al-Mg-Si ingot was melt in an induction furnace. Once it melted, the liquid was poured into a crucible attached to a twin roller cast to maintain the liquid temperature at 700°C. Molten alloy was poured in the gap between the copper rollers to produce the strips. The rotational speed of the cast rolls was varied from 60-30 rpm. During this process, the melt solidified to form strips. A specimen of 50 mm length cut from the cast strips was subjected to physical and mechanical characterization. Variation in hardness and microstructure of the produced trip were discussed.