Papers by Author: Mahamad Noor Wahab

Abstract: Al-Si-Mg/AlN composites were prepared by stir casting technique. The amount of AlN added to Al-Si-Mg alloy was from 2 to 10 wt%. As-cast composites were solutionised at 540 °C for 4 h, quenched in warm water, 60 °C then artificially aged at 180 °C for 4 h. The microstructure of Al-Si-Mg matrix alloy contained dendritic α-Al, needle-like Si and very little inter-metallic compounds. As-cast Al-Si-Mg/AlN composites have rounded α-Al phase and needle-like Si where AlN particles dispersed surrounding α-Al. Needle-like Si transformed to spheroid after artificial aging. The size of α-Al phases of heat-treated composites containing 2 and 5 wt% AlN was bigger than that of as-cast composites whereas the heat-treated Al-Si-Mg/10% AlN composite has thin and elongated dendritic α-Al phases, and larger AlN particles.

Abstract: Dry wear properties of aluminum nitride (AlN) reinforced aluminum-11% silicon alloy (Al-11%Si) was studied using a pin-on-disc configuration wear tester. Different weight percentages of AlN (0 – 10 wt.%) powder were added to the Al-Si alloy, melt and stir cast via bottom pour technique to form composites of Al-Si alloy/AlN. The dry sliding wear test were performed at a room temperature (27°C), under 25N and 70N load with fixed velocity of 1ms-1 and sliding distance between 1 to 5 km. The addition of 10 wt% of AlN improved wear resistance of Al-Si alloy by 72% and 130% indicated by volume loss for 25N and 70N load respectively. Mixed-wear mechanism of delamination, adhesion and abrasion was observed for the composite when applied loads were 25N and 70N while delaminating mechanism was dominance for Al-Si matrix alloy. Both Al-Si alloy with and without AlN reinforced found with FE element from counter-face disk that shows material transfer was significant.

Abstract: Microstructure and mechanical properties of heat treated Al-Si alloy containing up to 10 wt% aluminum nitride (AlN) particles were investigate. In this work high purity AlN powder with different weight percentage of 0, 5, 7 and 10 were calculated as reinforced material to the metal matrix composites. The Al-Si matrix was prepared by a bottom pour stir casting technique. Heat treatment was performed by soaking and followed by an aged treatment. It was found that the AlN particles were scattered randomly distributed in the matrix composite. Ageing induced Si grain transformation into to spheroid shapes while Al dendrites tend to become finer. Ultimate tensile strength (UTS) had improved drastically from to 125MPa to 306MPa for un-aged Al-Si alloy and aged AlN 7 wt%. Fracture morphologies showed a pronounced feature with small dimples, tear ridges and micro neck particularly in the aged samples leading to a higher tensile value and increase in ductility. The presence of AlN particles in the alloys had improved the tensile strength by slowing down the plastic deformation during tensile test.

Abstract: The effect of AlN addition in Al-Si alloy composites on the mechanical properties and dry wear behaviour were studied using pre-selected parameter conditions. In this work, high purity of AlN powders with different weight percentage of 5, 7 and 10 were used as reinforced materials for the composites. Morphology of the reinforced composite indicated that both silicon grains and inter-metallic compounds were surrounded by the AlN particles. The presence of AlN in the Al-Si alloy showed a significant improvement in tensile properties in which 7wt% of AlN addition increased up to 25% compared to those of without any reinforcements. Fracture morphologies with small dimples, tear ridges and necking features indicated that ductile fractures had occurred on the Al-Si composites. At 25N load, alloys with 5wt% of AlN exhibited high wear resistances whereas at 70N, alloys with 10wt% of AlN showed a great improvement in wear resistance. SEM investigation also revealed that the presence of wear was also marked with prominent grooves, craters and scoring marks. Overall, alloys with 7wt% AlN addition possessed great improvement in hardness, tensile and wear resistance properties.

Abstract: Dry sliding wear properties of aluminum nitride (AlN) reinforced aluminum silicon (Al-Si) alloy were investigated by using a pin-on-disc configuration tester. In this work, different weight percentages (5 and 10 wt%) of AlN was added into the Al-Si alloys. The samples were prepared by a stir casting process via a bottom pour technique which was then aged with a T6 condition prior to the wear test. Detailed analyses on the morphologies were conducted using scanning electron microscope (SEM) with the aid of an energy dispersive x-ray analyser (EDX). Prior to the heat treatment, the distribution of hard aluminum nitride particles that surrounded the Si phase had improved the hardness of the composites by 15%. The hardness value was found to be significantly increased about 80% for aged samples compared to un-aged samples. This was mainly contributed from precipitations of Si grain and intermetallic compounds; Mg2Si and FeSiAl5 formation in the alloys. Thus, a significant increased in wear resistance up to 56% was also observed especially at the highest applied load of 70N. Surface investigation by a scanning electron microscope (SEM) revealed that a combination of abrasion and adhesion wear mechanism was dominant for both un-aged and aged samples.