Papers by Keyword: Artificial Aging

Abstract: Conventional welding of lightweight metals like aluminium and magnesium alloys raises concerns about joint strength and ductility. Conversely, friction stir welding (FSW) improves both by bonding materials through plastic deformation. This study revealed a clear correlation between tool feed rates and the mechanical performance of the joints. At lower feed rates, controlled plastic flow resulted in robust joint formation, enhancing both Ultimate tensile strength and Yield strength. Conversely, escalating the feed rate compromised joint strength due to imperfect joints and inadequate plastic flow. Artificial aging was found to play a pivotal role in enhancing the mechanical properties of FSW joints. Higher feed rates, despite initially leading to reduced ductility, showed improvements in yield strength following aging, primarily attributed to the reduction of flaws and defects within the joints. Artificial aging contributed to elevated yield strength values through grain boundary sizing and precipitate formation. However, it's important to note that the improvement in strength was not uniform across all feed rates, indicating that the influence of post-aging treatment was more pronounced for joints produced at feed rates other than 450 mm/min. Ductility experienced a significant decline (almost 50%) after artificial aging, especially for joints formed at higher feed rates, highlighting the trade-off between strength and ductility. Findings aid FSW optimization, designing joints with desired mechanical traits for applications valuing strength, ductility, and aging effects.

Abstract: Aluminium alloys are widely used in the automotive and aerospace industries, where permanent fastening methods are commonly employed to join aluminium sheets and components. Many aluminium alloys are known for their high strength-to-weight ratio, while others are favoured for their availability and cost-effectiveness. In modern applications, dissimilar aluminium alloys are often joined to achieve enhanced performance. This study explored the effects of artificial aging on the microstructural and mechanical properties of weld joints at varying temperatures. Significant microstructural differences were observed between the heat-affected zone (HAZ) and the weld zone (WZ). Coarse grains in the HAZ enhanced ductility, while the fine-grained structure and increased precipitate formation in the WZ improved strength but reduced ductility. Aging at 165°C induced notable changes, with precipitate formation causing a 30% reduction in elongation and a 3.6% increase in ultimate tensile strength (UTS), attributed to precipitation hardening and improved bonding. At 175°C, mechanical properties further improved, with a 16% increase in yield strength (YS) and up to a 7.7% rise in UTS. The higher temperature facilitated greater precipitate formation, as confirmed by microstructural analysis, enhancing joint strength. However, this improvement came at the cost of ductility, with a 39.3% reduction in elongation due to restricted dislocation movement caused by the precipitates. Thermal conductivity variations in the welded plates influenced heat distribution and precipitate formation during aging. The process also reduced residual stresses from welding, enhancing diffusion and metallic bonding. Overall, artificial aging improved strength and stiffness but significantly decreased ductility, with aging at 175°C yielding optimal mechanical performance despite the trade-off in ductility.

Abstract: One of the techniques to increase the hardness of aluminum alloy is by aging process. The aging process includes natural aging and artificial aging processes. This study aims to investigate the effect of artificial aging on the hardness of aluminum silicon alloys. Artificial aging is carried out at two temperature variations, namely 150 and 200 °C. Metallographic test using optical microscopy and scanning electron microscopy were performed to observe the microstructure and deposits of silicon. Investigation of the constituent elements of aluminum silicon was carried out using the Energy Dispersive X-Ray Spectroscopy technique. The mechanical properties of aluminum silicon alloys examined were hardness before aging and hardness after artificial aging at temperatures of 150 and 200 °C. Hardness testing is conducted by Rockwell B hardness testing. The hardness test results showed that the hardness before the aging process was 61.1 HRB, the hardness after artificial aging at 150 °C was 69.11 HRB and the hardness after artificial aging at 200 °C was 80.36 HRB. There was an increase in hardness after the artificial aging process was carried out.

Abstract: In order to study the pre-straining and natural aging effects on the age-hardening response of EN AW 6082 and EN AW 6023 aluminium alloys during artificial aging at 170°C, the pre-straining by 5% was performed immediately after solution treatment of alloys at 550°C and subsequent quenching. The age-hardening response during artificial aging applied after various natural aging time (from 0.1 to 5 000 hours) was investigated using Vickers microhardness measurements and transmission electron microscopy characterization. It was found that pre-straining of quenched alloys state caused a dislocation density increasing in solid solution, which resulted in an immediate microhardness increase of alloys. During the subsequent natural aging of EN AW 6082 alloy, its microhardness increased right after alloy quenching and pre-straining, but only to the values obtained for the unstrained alloy state. On the contrary, the hardness of pre-straining EN AW 6023 alloy that is alloyed by Sn did not increase either after 10 hours of natural aging. This phenomenon is attributed to the effect of Sn on suppression of the strengthening clusters formation. The hardness of alloys increased greatly during artificial aging after pre-straining and natural aging due to accelerating the formation of coherent β″-phase particles. The negative effect of natural aging on the maximum age-hardening response obtained during alloys artificial aging had been observed for most of the pre-strained and naturally aged alloys states, with exception of EN AW 6023 alloy states that were pre-strained and shortly naturally aged (up to 100 hours).

Abstract: The effect of natural pre-aging time (from 0.1 to 10000 h) on mechanical response during subsequent artificial aging of EN AW 6063 aluminium alloy at 170°C was investigated using Vickers microhardness measurements, tensile test analysis and transmission electron microscopy characterization. The microhardness and tensile strength of EN AW 6063 alloy increased slightly with natural aging time. Afterward, the artificial ageing from 18 to 20 hours induced the maximum increasing of hardness and strength for variously naturally pre-aged states of alloy. But, it was found that when pre-aging time was prolonged from 0.1 h to 10000 h, the mechanical response of artificial aging applied for the pre-aged alloy states was slightly improved. It was suggested, that as pre-aging time was increased, the size of β'-phase particles formed in solid solution of pre-aged alloy state during artificial aging was decreased and their amount was increased.

Abstract: The contribution describes changes in morphology of structural parameters in recycled (secondary) AlSi9Cu3 cast alloy microstructure. These changes depended on different temperatures of artificial aging. The T6 heat treatment, which was used for affecting the structural parameters morphology, consisted of solution treatment at temperature 515 °C with holding time 4 hours, water quenching at 40°C and artificial aging at different temperatures 130 °C, 150 °C, 170 °C, 190 °C and 210 °C with different holding time 2, 4, 8, 16 and 32 hours. The morphology of structural parameters was observed using combination of different analytical techniques (light microscopy upon black-white and colour etching, scanning electron microscopy - SEM upon deep etching). The different temperatures of artificial aging led to changes in microstructure include the spheroidization and coarsening of eutectic silicon, gradual disintegration, shortening and thinning of Fe-rich intermetallic phases, the dissolution of precipitates and the precipitation of finer hardening phase (Al₂Cu).

Abstract: AlMgSi alloys (6XXX series) provide a good strength due to the precipitation of β” and β (Mg₂Si) phases. They have also very good formability which is required for different forming process after appropriate heat treatments.This work was carried out to investigate the effect of the addition of copper and the excess of Si on the response of natural and artificial aging of two Al-Mg-Si alloys. The aging parameters on precipitation sequence of two Al-Mg-Si alloys with and without excess Si were studied by DSC, MET and Vickers hardness measurement. The combined effect of Cu, Fe and excess of Si was found to accelerate the precipitation of the hardening phases. The additions of copper to the AlMgSi refine the average of the grain size and have a greater hardening effect compared to the excess silicon addition.

Abstract: The effects of Sn addition on clustering and age-hardening behavior in an Al-0.6Mg-1.0Si (mass %) alloy were investigated. Addition of Sn delayed the age-hardening in single aging at 170 ̊C. On the other hand, Sn promoted the age-hardening response in 3-step aging process which comprises a pre-aging (PA) at 90 ̊C for 18ks followed by natural aging (NA) for 604.8ks and artificial aging (AA) at 170 ̊C. The characteristics of clusters formed during PA and NA were evaluated by differential scanning calorimetry (DSC) analysis and atom probe tomography (APT). The DSC results show that the endothermic peak at around 160 ̊C to 200 ̊C was observed in the Sn-free alloy. On the other hand, in the Sn-added alloy, endothermic peak was not observed. It is suggested that Sn addition suppresses the formation of the clusters formed during NA. The APT results show that the Sn addition decreases the number density of clusters, especially smaller clusters. No Sn precipitates were found in Mg-Si precipitates formed during AA at 170 ̊C for 3.6ks. It is speculated that suppression of smaller cluster formation by addition of Sn promotes the age-hardening response

Abstract: The consequence of sub-zero treatment on the mechanical properties of welded AA6082-T6 by Gas Tungsten Arc Welding (GTAW) which in turn softens the heat concentrated welded region owing to dissolution of the strengthening precipitates. The sub-zero i.e. Shallow Cryogenic Treatment (SCT) is carried out on GTAW welded plate having a thickness of 6 mm at -77°C by varying the electrode travel speed and sub-zero treatment periods. Welded region of AA6082 were tested for hardness and microstructure by adapting three different conditions such as welded, post weld artificial aging with and without sub-zero treatment. Result revealed that the amount of softening in the welded region is indirectly proportional to electrode travel speed during welding process. It is also observed that the post weld SCT with artificial aging has increased the micro hardness values on the welded region as a consequence of the reactivation in the sequence of precipitation.

Abstract: In this paper the authors present some of the results of research on the behavior of high entropy alloys used in ballistic protection structures. Bullet impact testing methodology and results on layered Ballistic Packages that incorporate high entropy alloys (HEA) are presented. The paper details the technological processes used to improve the mechanical characteristics of Ballistic Packages. The optimization of the high entropy alloy based layered ballistic composite structures is also investigated. Testing methodology of ballistic boxes, the special heat treatment processes, the homogenization and the artificial aging of high entropy alloys, designed and applied during scientific research; represent the novelties of the article. Ballistic Packages are layered structures which include combinations of the following materials: HEA, armored steel, ceramic plates and laminated polyamide fibers arranged in a predetermined order depending on the constructive version. Ballistic Boxes behavior was investigated by ballistic experimental methods and numerical simulation methods. For the numerical simulation a FEM with an explicit numerical code was used. The numerical and test results are consistent in underling the ballistic protection effectiveness of the investigated configuration.