Effect Of Pre-aging Research Articles

Effect of Pre-aging on Microstructure and Mechanical Properties of Cryorolled AA2024 Sheets

Effect of Pre-aging on Microstructure and Mechanical Properties of Cryorolled AA2024 Sheets

Improvement in Strength of High Concentration Corson Alloy with the Heterogeneous-Nano Structure

Effects of pre-aging of Corson alloys with high concentrations of Ni and Si (Cu–4.2 mass%Ni–0.93 mass%Si) followed by heavy cold rolling and full-aging on strengthening were systematically investigated. Especially, development of heterogeneous-nano (HN) microstructure was focused. And the relationship of mechanical/electrical properties was precisely examined. The pre-aged alloys exhibited a considerable strengthening after 90% cold rolling. This was attributed to the increase in the volume fraction of deformation twin domains in the HN microstructure after cold rolling as well as the precipitation strengthening. The sample prepared by a thermo-mechanical process via pre-aging at 723 K, subsequent cold rolling and full-aging at 673 K for 600 s exhibited the best strength/conductivity balance with an ultimate tensile strength (UTS) of 1096 MPa and electrical conductivity (E) of 29% IACS. When examined the effects of solid-solution (SS) temperature on the microstructure and properties, SS at 1223 K derived finer grain size than at 1323 K and the achieved best balance of UTS and E with 1061 MPa and 33% IACS. Therefore, grain refinement prior to pre-aging had no significant effect on strengthening but contributed to modification of electrical conductivity.

Effect of Pre-Aging on Properties of CuCrSn Alloy during Rolling and Aging

The effect of pre-aging on properties of Cu0.24Cr0.20Sn alloy before rolling and aging was studied in details. The results displayed the pre-aging was useful to improve the microhardness and conductivity of Cu0.24Cr0.20Sn alloy before cold rolling and aging, and the effect increased with the extension of pre-aging time. The microhardness and electrical conductivity of Cu0.24Cr0.20Sn alloy by first pre-aging at 400 °C for 2 h, second 85% rolling and then aging at 300 °C for 1 h can reach 189 HV and 85.4 %IACS, respectively. The TEM results indicated the density of precipitates increased with the increase of pre-aging time, and the interaction between precipitates and dislocations was gradually strengthened in the subsequent room-temperature rolling. The increase caused by pre-aging treatment before rolling and aging was mainly due to dislocation density strengthening.

Effect of Pre-Aging, Over-Aging and Re-Aging on Exfoliation Corrosion and Electrochemical Corrosion Behavior of Al-Zn-Mg-Cu Alloys

By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-aging (120°C/24h + 160°C/8h + 120°C/24h), were characterized. It is found that compared with the Al-Zn-Mg-Cu alloys treated by T76 (120°C/24h + 160°C/8h), the new multi-stage aging treatment can improve the tensile strength, fracture toughness, hardness and conductivity of the alloys at the same time. This is mainly due to the pre-aging, over-aging and re-aging process of super high strength aluminum alloys. Compared with the two-stage over aging process, the formation of multi-stage multi-phase precipitation structure can improve the strength, toughness and corrosion resistance of the alloys at the same time. The polarization curve is consistent with the conclusion. Therefore, we conducted this study to test how the comprehensive properties of the alloy can be improved.

Effects of Pre-ageing on Microstructure and Mechanical Properties of T9I6 Treated 2519A Aluminium Alloy

The effects of pre-ageing on the microstructure and mechanical properties of T9I6 treated 2519A aluminium alloy were investigated by hardness testing, tensile testing, transmission electron microscope, high resolution transmission electron microscope and differential scanning calorimetry. With the increase of pre-ageing time from 40 min to 4 h, the strength tends to increase first and then decrease; the pre-ageing time of 80 min results in the highest 0.2% proof strength and ultimate tensile strength of 491.9 and 513.8 MPa, respectively, and a high elongation of 14.6%. Pre-ageing is favorable for the formation of a number of primary GP zones, which can greatly improve the distribution of dislocations introduced by subsequent pre-deformation and secondary GP zones introduced by subsequent interrupted ageing. As a result, the number of precursors for θ′ hardening precipitates is maximized and the mechanical properties is improved after final re-ageing.

Effect of Pre-Ageing on the Age Hardening Response of Cryorolled Al-Mg-Si Alloy

The present work investigates about the effect of pre-ageing on hardening behavior of Al-Mg-Si alloys processed by cryorolling and its age hardening behavior. Ageing conditions were examined at natural ageing for 2days and pre-ageing at 100 °C, 130°C and 170 °C for 4 hours, 2 hours and 30 minutes respectively. The observations revealed that, the pre-ageing before cryorolling is useful to enhance the dislocation density during cryorolling. However artificial ageing of cryorolled samples is not influenced much with pre-ageing. It is revealed that, maturing at room temperature of CR samples for 30 days has resulted better hardening response during artificial ageing.

Effect of Pre-Ageing on the Precipitation Behaviors and Mechanical Properties of Al-7Si-Mg Alloys

For alloys that are quenched to 25℃ room temperature, there are Mg-Mg, Si-Si and Mg-Si clusters shown by exothermic peaks in a A357 alloy. However, there are no clear Mg-Mg, Si-Si and Mg-Si cluster exothermic peaks in a A356 alloy. Hence, the low Mg content in a A356 alloy has less impact with natural ageing. The natural ageing impact on the mechanical properties of a A357 alloy is higher than a A356 alloy due to the precipitation of Mg-Si clusters for which the nucleation size does not reach the critical size. The 90℃ pre-ageing process could promote Mg-Si clusters to a critical size to become the nucleation site for of β''. This then increases the artificial ageing strength and mitigates the impact of natural ageing.

Effect of Pre-aging on Stress Corrosion Cracking of Spray-formed 7075 Alloy in Retrogression and Re-aging

The effects of pre-aging in retrogression and re-aging (RRA) treatment on microstructure, mechanical properties, and stress corrosion cracking (SCC) behavior of spray-formed 7075 aluminum alloy were investigated by tensile test, slow strain rate test, and transmission electron microscope. The results show that the under aging (120 °C for 16 h) as the pre-aging in RRA treatment can vastly improve the mechanical properties and the SCC resistance of the alloy, compared with early aging (120 °C for 8 h), peak aging (120 °C for 24 h), and over aging (120 °C for 32 h) treatments, the ultimate tensile strength of the alloy is 782 MPa, which is higher than that for peak aging or conventional RRA treatment; and the SCC resistance of the alloy is also excellent after RRA with under aging as pre-aging.

PRE-AGING OF RETROGRESSION AND RE-AGINGOF SPRAY FORMED 7075 ALLOY

Retrogression and re-aging(RRA) treatments are divided into pre-aging, retrogression and re-aging. Although peak aging was used as the pre-aging of RRA treatment in the past, some different opinions were reported in recent years. The effects of pre-aging of RRA treatment on microstructure, mechanical properties and conductivity of spray formed 7075 aluminum alloy were investigated by TEM, tensile and conductivity test. The results show that the mechanical properties and conductivity of spray formed 7075 alloy could be improved by the under aging at 120 ℃ for 16 h as the pre-aging of RRA treatment. The properties of the 7xxx series aluminum alloys depend on matrix precipitates(MPt), grain boundary precipitates(GBPs) and precipitate free zones(PFZs).The tiny MPt can increase the tensile strength. The connected GBPs and narrow PFZs will lower the conductivity and the elongation of the alloy. The under aging is more beneficial for the re-dissolution of the MPts at retrogression treatment at 200 ℃ for 10 min, and is more conducive to interrupt distributions of the GBPs than the early aging after RRA treatment. With the under aging as the pre-aging treatment, the growth of the MPts was actively suppressed and the GBPs at grain boundaries are continuous. During retrogression treatment, the MPts were re-dissolved absolutely and the GBPs were transformed from a chain to dissociation. After re-aging treatment, lots of tiny dispersive MPts precipitated out again in matrix, the GBPs were totally separated and the PFZ were widened.After pre-aging at 120 ℃ for 16 h and RRA treatment, the tensile strength and yield strength of the alloy are 782and 726 MPa, respectively, which are higher than that after peak aging treatment or conventional RRA treatment,the conductivity of the 7075 alloy is excellent with 22.7 MS/m.

Effects of Pre-Aging and Natural Aging on Bake Hardening Behavior in Al-Mg-Si Alloys

The effects of pre-aging and natural aging on the bake hardening behavior of Al-0.62Mg-0.93Si (mass%) alloy with multi-step aging process were investigated by means of Vickers hardness test, tensile test, differential scanning calorimetry analysis (DSC) and transmission electron microscopy (TEM). The characteristics of nanoclusters (nano scale solute atom clusters) formed during pre-aging and natural aging were also investigated using the three dimensional atom probe (3DAP) analysis. The results revealed the occurrence of natural age hardening and that the bake hardening response was decreased after the extended natural aging even though the pre-aging was conducted before natural aging. Since the 3DAP results exhibited the Si-rich clusters were newly formed during extended natural aging, it was assumed that the Si-rich clusters caused the natural age hardening and the reduced bake hardening response corresponding to Cluster(1). The decrease of the bake hardening response was markedly higher in the later stage of bake hardening than in the early stage. The size of the β’’ precipitates were reduced with increasing the natural aging time. Exothermic peaks of Peak 2 and Peak 2’ were observed in the DSC curves for the alloys pre-aged at 363K. Peak 2’ became larger with the natural aging time. This is well understood by the following model. The transition from Cluster(2) to the β’’ phase occurs preferentially at the early stage of the bake hardening. Then the growth of the β’’ phase is inhibited by the presence of Cluster(1) at the later stage of bake hardening. The combined formation of Cluster(1) and Cluster(2) by the multi-step aging essentially affects the bake hardening response and the β’’ precipitates in the Al-Mg-Si alloys.

Effects of Pre-Ageing on Thermomechanical Treatment Process of 2A12 Aluminum Alloy

The thermomechanical treatment of a 2A12 aluminum alloy was researched and the influence of pre-ageing on microstructure and hardness was analyzed emphatically. The results reveal that the hardness of specimen increases when they are pre-aged, the hardness value rises at first and then decreases, reaching the maxmum value when pre-aged at 180°C×30min . After plastically deformed at 450°C, the hardness keeps on increasing, and the grains are equiaxed polygon structure. After all the workpieces are aged in the end, the small particles of the second phase precipitates completely and disperses within the original phase matrix, the particles interact with dislocations in upper state that formed during plastic deformation and lead to a great increase in hardness compared with as-received. the best pre-aging parameter is 180°C×30min.

Effects of Pre-Aging on Bendability of an Asymmetric-Rolled Al-Mg-Si Alloy

The effects of pre-aging before natural aging on the bendability of an asymmetric-rolled Al-Mg-Si alloy were investigated. In the specimen without pre-aging, hardness increased with natural aging time due to the formation of nanoscale cluster (nanocluster; Cluster (1)). The suppression of Cluster (1) during natural aging is clearly seen in the pre-aged specimens though the formation of Cluster (2). It was found that tensile properties were not so affected by the types of clusters. Bending test clearly showed that the pre-aging improves the bendability of this alloy. This effectiveness of pre-aging means Cluster (2) well contributes the deformability of this alloy compared with Cluster (1). Such an improvement of bendability is considered to be derived from the structure of nanoclusters and its interactions with the factor of plastically deformation of alloys.

The Effect of Pre-Ageing on the Mechanical Properties of AA6061 Sheet Products

Various designated precipitation hardening and cold working have been employed to improve mechanical properties of aluminum–magnesium–silicon alloys. The aim of this study is to study how both high strength and excellent ductility could be achieved. Two main processes are competing to each other when the cold working is combined with precipitation hardening. They are dislocation annihilation during age treatment which improves ductility; and dislocation pinning by precipitates which increases strength of materials. In this paper, the mechanical properties of cold rolled AA6061 sheets in pre-aging, single and double aging conditions were compared. The different sequences of precipitation hardening and cold working were employed to achieve both high strength and excellent ductility. The results show that the amount of initial cold rolling and pre-aging may have negligible effect on the strength and hardness but significant effect on the ductility of alloy.

Effect of Pre-Ageing on the Artificial Ageing Response of Al-Mg-Si(-Cu) Alloys

The effect of different pre-ageing treatments on the subsequent artificial ageing response of Al-Mg-Si(-Cu) alloys have been investigated using hardness, tensile and electrical conductivity testing. The microstructural evolution was characterised by differential scanning calorimetry (DSC) and 3-dimensional atom probe (3DAP) analysis. Pre-ageing treatments were carried out at 160-250°C for short times. Results show that the early stage artificial ageing response after 30 minutes at 170°C is strongly influenced by the pre-ageing and natural ageing conditions. A pre-ageing treatment performed for a short time at a high temperature and within a short delay after solution treatment and quenching was found to give a promising hardening response during subsequent artificial ageing. The mechanisms by which pre-ageing can reduce the detrimental effect of natural ageing on the artificial ageing response will be discussed in relation to the formation and distribution of clusters, GP zones and/or precipitates.

Effect of Pre-Aging on the Microstructure and Strength of Supersaturated AlZnMg Alloys Processed by ECAP

This work is focused on the effect of the combination of natural aging and severe plastic deformation (SPD) produced by Equal-Channel Angular Pressing (ECAP) on the microstructure and strength of supersaturated AlZnMg alloys. Following a solution heat-treatment and quenching into water at room temperature, samples were naturally aged for different time periods and then processed by ECAP. The microstructure and mechanical properties of these samples are described and discussed. This investigation leads to proposing an interesting application of ECAP for supersaturated alloys. Using the shear bands created by ECAP in only one pass and applying appropriate subsequent aging treatments, composite-like microstructures can be achieved in conventional age-hardenanble Al alloys.

The effect of thermal ageing on the microstructure and fatigue strength of alloy 800HT

This study explores the effect of ageing on the fatigue strength of alloy 800HT. In-service ageing-induced microstructural changes are simulated by pre-ageing the alloy specimens prior to fatigue testing. Ageing treatments at 650°C, 760°C and 870°C were carried out for periods of 24 h, 100 h, 500 h and 1000 h. An examination of aged specimens by optical and scanning electron microscopy reveals that intergranular and intragranular M23C6 type precipitates form during the ageing treatment. These precipitates produce a significant reduction in the fatigue strength of the alloy. The detrimental effect of pre-ageing is more pronounced at higher ageing temperatures and longer ageing times. These precipitate particles reduce the alloy fatigue strength via extensive secondary cracking due to the brittling effect of the precipitate particles.

The Effect of Pre-Ageing and Addition of Copper on the Precipitation Behaviour in Al-Mg-Si Alloys

Hardness measurements and 3-dimensional atom probe analysis have been used to characterise the precipitation behaviour in two 6xxx series aluminium alloys, one Cu-free alloy (Al-0.78at%Mg- 0.68at%Si) and one Cu-containing alloy (Al-0.78at%Mg-0.68at%Si-0.30at%Cu). The heat treatments consisted of either natural ageing or pre-ageing at 353K followed by a paint-bake treatment at 453K. Natural ageing was seen to increase the hardness, and hence reduce formability compared to pre-ageing. In addition, the strengthening effect of artificial ageing was less after natural ageing than after pre-ageing. In the Cu-free alloy, needle-like β″ was observed to form only after a pre-ageing treatment during the first 60 minutes of a paint-bake treatment. In the Cucontaining alloy, needle-like β″ formed during paint bake in both the naturally-aged and pre-aged material, although it is formed more rapidly after pre-ageing. This was accompanied by an increase in strength over the Cu-free alloy and indicates that Cu reduces the deleterious effect of natural ageing.

Effect of Pre-Aging on the Aging of AlZn Alloys

Effect of Pre-Aging on the Aging of AlZn Alloys

Effects of compositions on the two-step ageing of AI-Mg-Si alloys

Effects of Mg (0.20.9 at.%) and Si (0.10.6 at.%) contents and trace of additional elements (0.010.2 at.%) on the two-step ageing phenomena of AI-Mg-Si alloys were studied by the measurements of hardness and electric resistivity and also by electron microscopy.The phenomena of two-step ageing of AI-Mg-Si alloys highly depended upon the contents of Mg2Si and additional elements as well as the conditions of pre-ageing. The pre-ageing led to either refining or coarsening of acicular precipitates in finally aged condition, according to the composition of alloys. Consequently, it resulted in either increase or decrease (negative effect) in strength of the alloys.For AI-Mg-Si alloys containing more than about 1.1 at.% of Mg2Si the pre-ageing at room temperature caused coarsening of finally aged structure but it caused refining of precipitates for the alloys containing less than about 0.9 at.% of Mg2Si. The negative effect of pre-ageing is interpretated as follows. It is based on the deleterions effect of impoverishment of solute atoms in matrix resulting from the clustering at room temperature, forming small clusters which modestly contribute to the strength.The negative effect of pre-ageing of Al-0.70 at.% Mg-0.35 at.% Si (1.05 at.% Mg2Si) alloy was decreased by the addition of transition elements such as Mn, Cr, Zr, V, and Fe, but increased by the addition of Ag, Cu, Be, Cd, and Zn. This may be caused by fast that the apparent supersaturation of Mg2Si in the alloys is increased by the latter elements, but decreased by the former elements which easily form insoluble compounds with Si and Al atoms.