Papers by Keyword: Artificial Ageing

Abstract: 2195 Al-Li alloy is famous for high strength, excellent fatigue strength and good stress corrosion resistance, which is widely used in the manufacture of high-performance aerospace components. The aim of this study is to validate how the stress relaxation aging behavior effect on the mechanical properties of 2195 Al-Li alloy. Through mechanical property test, the research was found that the performance after stress relaxation aging is higher than artificial aging (AA). In addition, the analysis of scanning electron microscopy SEM and TEM revealed that dislocations should be introduced by the stress relaxation aging process, which is more conducive to the precipitation of the T1 phase and strengthened the material with prolong ageing time. The results show that stress relaxation aging can significantly promote the precipitation of the T1. Therefore, this paper sheds new light on how SRA can improve mechanical properties and that SRA make better improve the distribution of precipitates in the grain boundary.

Abstract: In this study both natural ageing (NA) and artificial ageing (AA) behaviour of Al-Mg-Si aluminium alloy having trace addition of 0.04 wt.% Sn (Tin) was studied at different solution heat treatment (SHT) temperature and time, ageing time and temperatures. Microstructural analysis was performed to identify the intermetallic phases. It was observed that peak NA hardness strongly depends on the SHT temperature and time. SHT at 530 for 0.5 hour, slows down the peak NA hardness attaining time of the alloy to a maximum of 5 days. But as the SHT time increases to 3.5 hours, the peak NA hardness attaining time reduced to 1 day. Alloy SHT at 530 for 1 hour attain a maximum peak hardness of HRB 24 during 3 days of NA. Artificial ageing improved the hardness of the NA alloy to a maximum of HRB 41 during 12 hours of ageing at 190 . The overall hardness of Al-Mg-Si-Sn as-cast alloy increases by 32 % during ageing process.

Abstract: Al-Si-Mg casting alloys, such as Al-7Si-0.3Mg alloy A356, are heat treatable and can be precipitation hardened to the T6 temper condition. However, Al-Mg-Si casting alloys (5xx series) are generally not considered to be heat treatable. These 5xx series castings are known for good castability and good resistance to corrosion, especially in marine environments. This paper investigates the extent to which 5xx series alloys could possibly be artificially aged. The influences of artificial ageing time on the overageing characteristics of both Al-Mg-Si and A356 casting alloys have been studied. A356 aluminium alloy castings were produced using the CSIR rheo-high pressure die casting process (R-HPDC). Al-Mg-Si alloys were cast using permanent mould casting. The rate of overageing of these alloys is of importance for potential higher temperature applications. The overageing characteristics of Al-Mg-Si and A356 aluminium alloys have been investigated at an artificial ageing temperature of 190°C for ageing times up to 128 hours. It is shown that the rate of overageing of Al-Mg-Si casting alloys is lower than for alloy A356. This could possibly result in the use of these alloys in applications at temperatures that are higher than where alloy A356 can be employed. It also allows the possibility of using the 5xx series alloys as an alternative to other Al-alloys for R-HPDC applications.

Abstract: FAST (Fast light Alloys Stamping Technology) has recently been developed to efficiently and economically manufacture lightweight, high strength structural components from aluminium alloys sheet. Post-form strength prediction of 6xxx series aluminium alloy (AA6xxx) after FAST and multiple stage heat treatments has been a challenge. This is due to the effect of pre-existing dislocations induced via high temperature plastic deformation in the forming process. In the present research, a new PFS (post-form strength) model has been proposed to predict the age-hardening response of AA6xxx alloys undergoing FAST and subsequent thermal cycles. The model incorporates two sub-models, for simulating viscoplastic flow and predicting strength evolution respectively. The first sub-model incorporates a set of constitutive equations, developed to model the stress-strain curve of AA6xxx during FAST. The second sub-model employs precipitation-hardening and dislocation-hardening theories to simulate the evolution of microstructure and, as a consequence, strength of alloys undergoing artificial ageing cycles. This is calculated by considering the intrinsic resistance of the alloy to dislocation movement due to solute atoms and precipitates. The strength was computed accurately via the internal state variables method, in which dislocation density, volume fraction of precipitates, solute concentration and radii of precipitates were correlated. Furthermore, the model was validated by comparing results with transmission electron microscope (TEM) images as well as hardness measurements. Hence, the model performs as a powerful and comprehensive tool to simulate post-form strength of 6xxx series aluminium alloys that undergo complicated thermomechanical processes including high temperature deformation and post-form heat treatment, with less than 5% deviation between measured and predicted values.

Abstract: The scope of this work is to study of microstructural changes and mechanical properties during natural and artificial ageing treatment of AGS Alloy wire cold drawn with different deformation at ENICAB in Biskra. And as well to know the phase formation during different deformation of aluminum alloys wires. as well as the combined influence of the plastic deformation rate and the aging temperature. Wire section reduction shows a change in microstructure and texture. The methods of characterization used in this work are: scanning electron microscope and X-ray diffraction, micro hardness (Hv).

Abstract: Rolling is a very common technique for shaping sheet metal. It aims to reduce the thickness of a metal sample to adapt it to the usual conditions of use in the industry. Nevertheless, this technique is not without modifying the mechanical and microstructural properties of the materials that can influence the mechanical strength of shaped parts. The purpose of the present investigation is to study the changes in microstructures and micro-hardness of Al-Mg-Si alloy with different rolling reduction in thickness and following artificial aging treatments at 175° C . We notice that the micro-hardness increases with the increasing of the deformation level . Reduction in thickness shows a change in microstructure and texture. Characterization methods used in this work is: Optical Microscopy (OM) and, Vickers microhardness.

Abstract: The influences of electric current on the microstructures and mechanical properties of 6061 aluminum alloy were investigated by electric conductivity measurement, tensile test, scanning electron microscope and transmission electron microscope. When applying electric current both at solid solution and ageing treatment, the alloy has the highest peak strength, and the time to peak strength shortens by 12h. The electric current applying during either solid solution or ageing, increases the density and size of β'' phase.

Abstract: Ground water, rain and other environmental effects are important moisture sources which affect the durability and performance of basements, roofs, underground and other building structures in the direct contact with moisture. Waterproof materials such as bitumen sheets, polymeric foils and membranes provide basic protection of constructions against harmful moisture action. However, in some cases, the applicability of commonly applied waterproof insulation systems is limited as for example in tunnel constructions with complicated geometry or in areas with unstable subsoil. Here, advanced types of waterproof materials find use. On this account, sprayed waterproof coating based on polyurethane elastomer designed for protection of complicated shapes and extremely mechanically loaded structures is experimentally researched in the paper. The obtained data give clear evidence of a good resistance of studied coating against artificial accelerated temperature ageing. The studied material has high resistivity to impact and ductility. The interaction of accelerated aging and impact loading has no effect on vapor-and waterproof function of the insulation layer. In addition, polyurethane elastomer provides a sufficient adhesion to the typical buildings materials, such as concrete, ceramic brick, etc.

Abstract: Load-bearing joints of glass structures belong to the one of new applications of adhesive connections in civil engineering. They provide several important benefits particularly even stress distribution along the contact depending on geometry and stiffness of the glue joint, which is crucial for brittle glass. There is a lack of knowledge about semi-flexible or semi-rigid adhesive connections in the structural glass field and durability is one of the essential properties that have to be assessed during design-process of bonded connection. An extensive research focused on shear glued joints in glass structures was performed at CTU in Prague, which also comprised environmental effect simulation on the glued specimens in laboratory accelerated conditions. The paper is dedicated to impact of ageing to the specimens and their mechanical properties together with brief overview of available laboratory ageing methods.

Abstract: In modern car bodies lightweight structures are used to achieve a reduction of energy consumption and CO₂-emissions. One of the most important lightweight materials is aluminum and its alloys. Current state of the art in automotive industry is utilizing precipitation hardenable aluminum alloys of the 6000 series whereas the crash-relevant strength is achieved by artificial ageing during the paint drying process. Due to newly developed coatings which provide faster curing at lower temperatures, post-forming ageing of the 6xxx alloys to satisfactory strength levels becomes more difficult. The aim of this study is to investigate the feasibility of employing high strength aluminum alloys of the 7000 series in order to reduce artificial ageing time and temperature while keeping required strength. Within this contribution, the influence of pre-straining and subsequent heat treatment on mechanical properties will be presented.