Effects of Grain Refinement on The Cooling Rate, and Microstructural and Mechanical Properties of Al-Si Sand Castings

This thesis covers the key areas of numerical simulation of sand casting process to evaluate the runner and gating system of sand mold. The major experimental work is focused on grain refinement and modification of LM6 A1-Si sand casting. The simulation software package used is MAGMAsoft and the sand casting process employed is COz sand casting. The numerical results of MAGMAsoft match qualitatively with the experimental data. This validates the use of MAGMAsoft to simulate sand casting process to assist in mold design and prediction of flow and solidification characteristics. The implementation of experimental work to ascertain flow and solidification characteristics of sand casting has been performed on a casting designed with varying thickness of different moduli. The casting metal used is LM6 A1-Si alloy. The cooling rate of sand casting has been correlated with the modulus of casting. The mechanical mechanical properties of hardness and ultimate tensile strength have been correlated with the solidification rate. The secondary dendrites arm spacing (SDAS) is also found to have linear correlation with section modulus. This provides important and useful information to product design of sand casting about how to optimize the section thickness to achieve the desired mechanical properties. An investigation is carried out to study how to further enhance the mechanical properties of LM6 A1-Si alloy sand casting by adding the commercial grain refiner of Al-5Ti-1B into the melt at different inoculation levels of 0.25, 0.5, 0.75 and 1.0% weight. The results show that 0.5% weight of A1-5Ti-1B grain refiner is the optimal level to grain refine and enhance the mechanical properties of LM6 sand casting. The microstructural analysis shows that grain size is reduced when the casting solidifies with faster cooling rate due to the addition of grain refiner. This renders significant effect to enhance the mechanical properties of the casting. The improvement of grain refinement is quantified by measuring the hardness, ultimate tensile strength (UTS) and elongation (strain) of the cast samples. Inoculation with 0.5% weight of Al-5Ti-1B grain refiner has attained UTS of 167.86 MPa, maximum hardness of 65.6 Rockwell and fracture strain of 0.0314. A further investigation has been carried out to add 0.5% weight of A1-1OSr and 0.5% weight of Al-5Ti-1B into the melt to cast the same part. Similar mechanical tests and microstructural analysis are performed to study the combination effect of strontium, titanium and boron on LM6 sand castings. It is discovered that the ultimate tensile strength of the castings is further improved to 174.46 MPa and the morphology has been modified. However, the hardness of Sr-modified LM6 sand casting only achieves a maximum value of 63.34 Rockwell which is not a significant improvement. Modification of LM6 by strontium only alters the morphology of the silicon eutectic to be more fibrous instead of acicular so that the structure would not be brittle relative to unmodified structure and it is found that the ductility after modification achieves a fi-acture strain of 0.032 which is higher than the 0.0267 of unmodified LM6. The cooling curve shows that the solidification is dramatically transformed to eutectic solidification at temperature around 540 O C . This mixture of grain refiner and modifier is termed "hybrid modifier" by the author

Quality Assurance of Aluminium Extrusion for 6xxx Series Alloys

Aluminium extrusion of 6xxx series alloys is gaining more and more importance and indispensable in the market for applications in automotive (great potential for EV in the near future by 2030), construction, architecture, electronics, marine and rail transport. The 6000 series alloys can be divided into soft alloy (e.g. 6060, 6063) and hard alloy (e.g. 6005A, 6061, 6082) for different applications based on customer’s requirements for tensile strength, yield strength, elongation, surface finishing (powder coating and anodizing) and heat treatment. To produce good quality extrudates with quality that can meet customer’s stringent requirements has become a challenging job nowadays for extruders in developing country like Malaysia. In order to be competitive in the global market, the products have to be produced at minimum cost and just-in-time to meet the committed delivery date. This will require a very good implementation of quality system in the production to ensure customer’s satisfaction is achieved from time to time. Based on the real experiences of working in an international scale extruder, the effective methods taken to improve product quality and productivity are elaborated throughout the chapter

The microstructure and mechanical properties of titanium dioxide nanotubes synthesized in the fluoride-based electrolyte

Titanium is one of the biomaterials commonly used for prosthetic devices due to its bio-inert properties. The discovery of titanium dioxide nanotubes (TDNTs) has created a great interest in medical applications such as dental and orthopedic implants. The synthesizing of TDNTs can produce different morphology, sizes and mechanical properties of the nanotubes – depending on the applied method. In this study, an electrochemical anodization method was used for synthesizing the TDNTs. A 100 ml mixture of 99% of ethylene glycol (EG), 1% of deionized water and 1 wt.% of ammonium fluoride (NH4F) was used as the electrolyte of the electrochemical cell. Parameters such as anodization time and the voltage applied were used to alter the morphology of the TDNTs formed. The produced nanotubes were analyzed and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness tester. The SEM results showed that the formed diameter of nanotubes was mainly affected by the anodizing voltage. The wall thickness was found to be irrelevant to the parameters conducted in this study. The diameter of nanotubes formed with an anodizing voltage of 30, 45 and 60 V have the diameters ranging from 46 nm to 71 nm. All of the TDNTs samples formed have a wall thickness between 11 nm and 13 nm. With the use of EG and NH4F as an electrolyte, the array of TDNTs with honeycomb structure was formed. In general, hardness test showed that the hardness of the nanotubes was inversely proportional with the anodizing time. The anodizing voltage only has little effect on the hardness of the nanotubes. The nanotubes formed by 60 V have about 3 to 5% lower hardness compared to those formed by 30 V for different anodizing times

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms

Genetic associations at 53 loci highlight cell types and biological pathways relevant for kidney function.

Reduced glomerular filtration rate defines chronic kidney disease and is associated with cardiovascular and all-cause mortality. We conducted a meta-analysis of genome-wide association studies for estimated glomerular filtration rate (eGFR), combining data across 133,413 individuals with replication in up to 42,166 individuals. We identify 24 new and confirm 29 previously identified loci. Of these 53 loci, 19 associate with eGFR among individuals with diabetes. Using bioinformatics, we show that identified genes at eGFR loci are enriched for expression in kidney tissues and in pathways relevant for kidney development and transmembrane transporter activity, kidney structure, and regulation of glucose metabolism. Chromatin state mapping and DNase I hypersensitivity analyses across adult tissues demonstrate preferential mapping of associated variants to regulatory regions in kidney but not extra-renal tissues. These findings suggest that genetic determinants of eGFR are mediated largely through direct effects within the kidney and highlight important cell types and biological pathways

Effect of heat treatment on gravity die-cast Sc-A356 aluminium alloy

The effects of scandium addition (0.00 wt.%, 0.2 wt.%, 0.4 wt.% and 0.6 wt.%) and T6 heat treatment on the microstructure and mechanical properties of A356 aluminium alloy have been investigated in the research reported in this paper. The Sc inoculated specimens were prepared by gravity die-casting, according to ASTM B557-06 standard. The cast samples were then subjected to heat treatment at solutionizing temperature of 540 °C for 8 h followed by water quenching and artificial aging at 160 °C for 6 h. The microstructure, microhardness and tensile strength of the heat-treated samples were examined with use of scanning electron microscope (SEM), optical microscope, Vicker’s hardness tester, and Instron static machine respectively. Heat treatment was found to be able to effectively reduce grain size down to 16 μm (0.6 wt.% Sc), from 40 μm (original A356). The tensile strength was significantly improved, up to 338 MPa for heat treated 0.6 wt.% Sc-A356 having been achieved. The microhardness of 118 HV has been obtained for heat treated 0.6 wt.%Sc-A356

Effect of heat treatment on gravity die-cast Sc-A356 aluminium alloy

The effects of scandium addition (0.00 wt.%, 0.2 wt.%, 0.4 wt.% and 0.6 wt.%) and T6 heat treatment on the microstructure and mechanical properties of A356 aluminium alloy have been investigated in the research reported in this paper. The Sc inoculated specimens were prepared by gravity die-casting, according to ASTM B557-06 standard. The cast samples were then subjected to heat treatment at solutionizing temperature of 540 °C for 8 h followed by water quenching and artificial aging at 160 °C for 6 h. The microstructure, microhardness and tensile strength of the heat-treated samples were examined with use of scanning electron microscope (SEM), optical microscope, Vicker’s hardness tester, and Instron static machine respectively. Heat treatment was found to be able to effectively reduce grain size down to 16 μm (0.6 wt.% Sc), from 40 μm (original A356). The tensile strength was significantly improved, up to 338 MPa for heat treated 0.6 wt.% Sc-A356 having been achieved. The microhardness of 118 HV has been obtained for heat treated 0.6 wt.%Sc-A356

Modal and stress analysis of gear train design in portal axle using finite element modeling and simulation

The portal axle is a gearbox that is specially designed for off-road driving conditions. It is installed between the wheel and the axle shaft to give higher ground clearance to the vehicle. The modeling and simulation of spur gears in portal axle is important to predict the actual motion behavior. However, gear train design in portal axle is difficult to study comprehensively due to their relatively low cost and short product life cycle. In this study, modal analysis of portal axle is simulated using finite element method (FEM). Modal analysis is simulated on three different combinations of gear train system commonly designed for portal axle. The three gear trains being analyzed are gear train without idler gear, one idler gear and two idler gears. FEM static stress analysis is also simulated on three different gear trains to study the gear teeth bending stress and contact stress behavior of the gear trains in different angular positions from 0 degrees to 18 degrees. The single and double pair gear teeth contact are also considered. This methodology serves as a novel approach for gear train design evaluation, and the study of gear stress behavior in gear train which is needed in the small workshop scale industries

Genetic associations at 53 loci highlight cell types and biological pathways relevant for kidney function

Reduced glomerular filtration rate defines chronic kidney disease and is associated with cardiovascular and all-cause mortality. We conducted a meta-analysis of genome-wide association studies for estimated glomerular filtration rate (eGFR), combining data across 133,413 individuals with replication in up to 42,166 individuals. We identify 24 new and confirm 29 previously identified loci. Of these 53 loci, 19 associate with eGFR among individuals with diabetes. Using bioinformatics, we show that identified genes at eGFR loci are enriched for expression in kidney tissues and in pathways relevant for kidney development and transmembrane transporter activity, kidney structure, and regulation of glucose metabolism. Chromatin state mapping and DNase I hypersensitivity analyses across adult tissues demonstrate preferential mapping of associated variants to regulatory regions in kidney but not extra-renal tissues. These findings suggest that genetic determinants of eGFR are mediated largely through direct effects within the kidney and highlight important cell types and biological pathways