Papers by Keyword: T6

Abstract: In this study to the authors knowledge 1^st time, Metal Injection Molding (MIM) technique was used to introduce the magnesium alloy WE43 into binder-based powder metallurgical (PM) processing. Towards later adoption to binder-based 3D-printing technologies, Fused Granular Fabrication (FGF) technique, respectively for biomedical application. Metal Injection Moulding (MIM) is a binder based economic near net shape prototyping technique for production of complex shaped parts in high number and high reproducibility, and hence perfect as a “gold standard” for the introduction of new Mg-alloys into binder passed PM processing. In doing so, dogbone shape tensile test specimen were manufactured by MIM, subsequently solvent debound and conventional sintered in argon atmosphere. Next to the as sintered specimens (asS), solid solution heat treatment (T4) and precipitation hardening heat treatment (T6) were performed on additional specimens. Tensile tests pointed out high strength and ductility of as sintered and heat treaded specimens of up to 226 MPa UTS at 7.6% elongation at fracture. The microstructure was investigated using SEM imaging technique equipped with energy disperse x-ray energy analysis (EDX) for secondary phase analysis. Hence, the magnesium alloy WE43 could be identified as a high strength and ductility alloy for binder based PM processing for future additive manufacturing approaches in biomedical applications of patient adapted implants.

Abstract: Structural high vacuum die casting has been growing significantly over the past decades. It is typically done with special (primary type) alloys, special melt treatment practices, high vacuum, a carefully engineered die casting process applying many best practices in our industry. Structural die castings are growing in size and complexity and die casting machines are getting bigger and bigger - and those castings are becoming a significant challenge with current technologies. It was now found that Rheocasting - a process of preparing a semi-solid slurry (with 30-45% solid fraction) that is injected slower and in a laminar way into the cavity, can take structural die casting to completely new heights, enable the casting of parts that would otherwise be impossible to cast and at the same time reduce or eliminate some of the current problems of structural die casting. With Rheocasting, lower purity (secondary) aluminum alloys can be used and excellent properties can be achieved as cast and heat treated (T5, T6/7). Rheocasting has had a breakthrough in the telecom and other industries, but it has now been optimized to become an essential tool in the toolbox of making structural castings. This paper shows the developments that lead to the successful series production of a large (about 4’ long) hinge pillar for an Electric Vehicle (EV). It explains the challenges and how they were overcome, and some of the possibilities of the process regarding alloys, heat treatments and achievable properties. It also shows how Rheocasting can help die casters produce more complex (thin and thick walled) and very large castings with the highest integrity. It can replace structural low-pressure permanent mold (LPPM) castings and reduce wall thickness, improve tolerances and make them more economical. Rheocasting can enable die casters to enter this new market of structural castings including Gigacastings, produce parts previously thought impossible to cast (and on much smaller machines than thought), and expand the growing structural die casting market even faster and further.

Abstract: High-strength aluminum alloys, such as the AA7075 alloy, offer great potential for lightweight construction thanks to their high specific strength. However, high strength and low ductility are a challenge for processing these materials. In our study, three different process routes (T6, W-Temper, O) for roll forming of a hat profile are investigated experimentally and in an FE-simulation. Since the targeted production of the hat profile is hindered due to material failure in T6-condition, inline induction heating and subsequent water spray quenching is used to bring the material to the W-Temper state before roll forming. As a third option, a pre heat treatment is applied to a soft annealed (O) material state. The experimental results show fundamental differences of the forming processes, depending on the tempering condition. The FE-simulation involves the roll forming process for the production of a hat profile and shows a high agreement with the experiments. Finally, the experimental results demonstrate how inline solution annealing by induction heating for the W-Temper process affects the properties and the quality of the profiles produced.

Abstract: The aim of this work is to investigate the optimum heat treatment for Al-5.7Si-2Cu-0.3Mg aluminium alloys and study its effect on microstructure, phase transformations, and hardness. The test specimens were taken from the as-received alloy. Solution treatment was performed at 485°C and 500°C under various solution treatment times for 4, 8, 10, and 12h, and the samples were then hot water quenched at 60°C, followed by aged hardening at 150°C, 170°C and 190°C for 2,6,10, and 14h, and subsequently air-cooled. The hardness of the Al-5.7%Si-2Cu%-0.3%Mg alloys were determined using a Rockwell hardness tester. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to determine the microstructure of the samples, while X-ray diffraction (XRD) was used to identify the phase compositions. The resulting microstructures and hardness values were compared to the corresponding as-cast samples. It can be seen that the solution treatment at 485°C for 12 h and aging at 190°C for 10 h are the optimum T6 heat treatment conditions that would result in hardening precipitates over the as-cast alloy. OM and SEM morphologies show significant microstructure evaluation of improved distribution of the Si particles. After T6 treatment, the morphology of Si particles in the as-cast Al-5.7Si-2Cu-0.3Mg alloy changes from long and coarse plate-like grains to fine spherical shaped grain. The XRD plots confirmed the relatively high concentration of Al, Si, and Al₂Cu in the heat treated Al-5.7%Si-2Cu%-0.3%Mg alloy relative to that of the as-cast alloy. The hardness of the T6 alloy also increased.

Abstract: Aluminum alloys are the first chosen materials for aircraft structures since 1930 due to their high ratio between properties and density. Currently, aircraft industries use Al-Zn-Mg-Cu alloys, with T7451 temper, which it shows high strength, fatigue and corrosion resistance. The improvements properties are result from the η’ phase formation, MgZn₂. The aim the present work is to propose an alternative route for ageing heat treatment at one AA7050 aluminum alloy, the manner which the formation of η’ phase particles at lower temperatures and longer periods of treatment is obtained. According to the literature, ageing treatments at low temperatures and longer periods optimize the usage of the solution atoms, favoring the growth and nucleation particles. As a result, there is an increase in the density of the particle improving the alloy properties. These improvements show a decrease up to 13% in the crack propagation rate for moderate ΔK levels, keeping the same levels of Vickers hardness but with decay of 12% of ultimate tensile strength.

Abstract: Automotive castings have to meet more and more versatile requirements these days. One of the most important requirements towards suppliers and foundries is producing parts of better quality, higher performance but at the same time of less weight. In order to couple this small weight with high performance and excellent quality these products should meet very strict mechanical standards of automotive parts. There is a constant need for production engineering developments ranging from purity degree - that is producing molten metal with high cleanness - to grain refinement and alloy improving including heat treatment technologies.

Abstract: The history of semi-solid metal forming and in particular rheo-high pressure die casting at the Council for Scientific and Industrial Research in South Africa is discussed. Processing flexibility is demonstrated on the Al-Si-Mg, Al-Mg-Si, Al-Cu-Mg and Al-Zn-Mg-Cu casting and wrought alloy systems as well as on high purity aluminium, unmodified Al-Si binary eutectic, metal matrix composites and magnesium alloys. Material properties are highlighted.

Abstract: Cast light metal alloys have retained their importance and unique characteristics as first candidates when cost-function relationship is considered. Hypoeutectic aluminum silicon alloys as (A356) exhibit several specific and interesting properties that qualify them to be used in many automotive and aeronautical applications. Evidence of significant enhancement in strength in the properties of Al-Si cast alloys by incorporating nano-particles have been recently presented. The present study aims at developing nano-dispersed Al-Si alloys with suitable casting methods that assure the dispersion of the nano-particles. In this work a number of cast samples of A356 were prepared by rheo-casting in a specially designed and built furnace unit allowing for the addition of the nano-particles into the molten Al-Si alloy in the semi-solid state with mechanical stirring. The microstructural features and the mechanical properties of the cast and T6 heat treated samples were investigated. The results obtained in this work showed enhancement in the mechanical strength of the nano-dispersed alloys, accompanied by significant increase in the elongation percentage, supported by evidence of refined dendrite arms length, and inter-lamellar spacing.

Abstract: In this study, the effect of various solution and aging treatments on microstructure and mechanical properties of an as cast Al-5.5Zn-1.2Mg alloy has been investigated by optical microscopy, hardness measurements and room temperature tensile test. The solution heat treatments performed at temperatures between 400 and 490°C have little effects on hardness while electrical conductivity values increased at the lower temperature because of dissolved atoms and vacancy rich clusters. Concerning aging, only T6 improves mechanical properties of the undeformed alloy, while aging performed on tensile tested samples results in a decrease of hardness due to accelerated kinetics and heterogeneous nucleation of equilibrium phase stimulated by dislocation network. Tensile tested samples of the as cast alloy exhibits the fastest recrystallization time during annealing because of the absence of fine precipitates and the high strain hardening.