Effect of pre-aging on precipitation behavior of Al-1.29Mg- 1.22Si-0.68Cu-0.69Mn-0.3Fe-0.2Zn-0.1Ti alloy

1 Introduction Aluminum alloys of the 6000 series, containing Mg and Si as the major solutes, are strengthened by the precipitation of metastable precursors of the equilibrium β(Mg2Si) phase. The precipitation of these metastable precursors occurs in on…     

Effect of Mg on microstructures and properties of Al-Mg-Si-Cu aluminium alloys for automotive body sheets

The effects of variation of Mg content on microstructures, the tensile properties and the formability of Al-Mg-Si-Cu alloys for automotive body sheets were investigated by means of scan electron microscopy, optical metallographic analysis, tensile and Ericsson tests. The results show that for Al-Mg-Si-Cu aluminium alloys with excessive Si, with an increment of Mg content, the strength enhances, the specific elongation and Erisson values of alloys decrease, and the number of Mg2 Si constituent increases and that of AI(MnFe)Si type constituents reduces. Al-Mg-Si-Cu aluminium alloys with excessive Si for automotive body sheets can present obviously the paint bake hardenability during the paint hake cycle (i. e. artificial aging at 170℃ for 30 min immediately after the solution treatment and quenching). Suitable Mg content should be controlled in the range of 0.8% and 1.2%(mass fraction).     

预时效处理对 Al-Zn-Mg-Cu 合金硬化响应及微观组织的影响

研究了预时效处理对Al-Zn-Mg-Cu铝合金薄板力学性能和微观组织的影响,测试了显微硬度和力学性能,表征了TEM微观精细组织。结果表明:固溶处理后在180 ℃立即进行人工时效处理,可获得Al-Zn-Mg-Cu合金的显著时效硬化效果,且在8 h后达到峰值硬度195 HV0.5,与基体呈共格关系的η′相为主要强化相;120 ℃×10 min为最佳的预时效处理制度,经14天的室温停滞后,相比于固溶+自然时效态,硬度降低了13 HV0.5,降幅达到10.7%,具有明显的抑制自然时效作用;预时效+自然时效态试样,经烘烤硬化处理后,屈服强度和抗拉强度分别达到了465和545 MPa,强度增量分别达到170和95 MPa,同时伸长率达到12.5%。     

固溶处理和人工时效对Al-Cu合金显微组织和力学性能的影响(英文)

对Al-Cu合金进行析出强化和人工时效处理以获得优异的力学性能,如高的强度、好的韧性。其热处理工艺条件为:510～530℃固溶处理2h;60℃水淬;160～190℃人工时效2～8h。采用光学显微镜、扫描电镜、能谱分析、透射电镜和拉伸实验对经固溶和人工时效处理的Al-Cu合金的组织和力学性能进行表征。固溶处理实验结果表明,Al-Cu合金的力学性能随着固溶处理温度的升高先增加,然后降低。这是由于Al-Cu合金的残余相逐渐溶解进入基体中,从而导致析出相的数量和再结晶晶粒尺寸不断增加。相较于固溶处理温度,固溶处理时间对Al-Cu合金的影响较小。人工时效处理实验结果表明,合金经180℃时效8h,可以获得最大的拉伸强度。合金的最大拉伸强度和屈服强度随着时效时间的延长和温度的升高而升高。     

The effect of pre-aging on the electromigration of flip-chip SnAg solder joints

The effect of pre-aging on electromigration is investigated in this study using flip-chip SnAg solder joints. The solder joints were pre-aged at 170°C for 1 h, 3 h, 5 h, 10 h, 25 h, and 50 h, and then they were subjected to electromigration tests of 0.9 A at 150°C. It was found that the average failure time increased about three times when the joints were pre-aged for 3 h to 25 h. But it decreased when the joints were overaged. It is proposed that the major contributor to the prolonged failure time may be the densification of the nickel and copper under-bump metallization (UBM) and the solder due to the aging treatment. The pre-aging treatment at 170°C may stabilize the microstructure of the solder. The vacancies in the solder were annihilated during the heat treatment, causing a slower diffusion rate. In addition, the UBM structure became denser after the pre-aging process. Thus, the denser UBM structure may lead to slower consumption rates of the nickel and copper layers, resulting in the enhancement of electromigration resistance.     

Using differential scanning calorimetry to characterize the precipitation hardening phenomena in a Cu-9Ni-6Sn alloy

An attempt has been made to characterize the transformations in a Cu-9Ni-6Sn alloy using heat flux differential scanning calorimetry (DSC) assisted by hardness measurements. Both solution heat treatment and precipitation transformations have been studied. Different starting conditions were imposed on the material to allow a clearer understanding of the transformations involved. The precipitation from the supersaturated solid solution happens in two temperature ranges, i.e., from 200 to 400 °C and from 440 to 600 °C. In the temperature range from 400 to 440 °C, the alloy does not usually transform. Thermal cycles leading to aging and overaging were determined. The precipitation hardening conditions at 350 °C or lower for less than 600 min, or 375 °C for up to 120 min, lead to metastable precipitation. Precipitation hardening for 120 min at 400 °C or 1200 min at 350 °C results in stable precipitation and is responsible for overaging the alloy.     

Improved Properties in Relation to Fine Precipitate Microstructures Tailored by Combinatorial Processes in an Al-Cu-Mg-Si Alloy

The 2xxx series Al alloys have been widely used in aerospace industry owing to their high strength, good plasticity and superior formability. To ensure a good control of shape, the quenched alloy sheets require a small pre-deformation before artificial aging. However, this pre-deformation considerably deteriorates the mechanical strength of the Al-3.0Cu-1.8Mg-0.5Si (wt%) alloys due to the formation of unfavorable large-sized precipitates at dislocations. To tackle this issue, we designed a pre-aging process prior to the pre-deformation. The thermal-mechanical treatment, involving pre-aging, pre-deformation and subsequent aging, markedly enhanced the ultimate tensile strength up to 521 MPa compared to that (448 MPa) of the alloy without pre-aging. Microstructure characterization revealed that the fine precipitates (~ 2 nm) with a uniform dispersion were promoted within the Al matrix, which in turn partly suppressed the formation of the unfavorable large-sized precipitate (~ 100 nm). Our findings provide a new clue for designing stronger Al alloys with age-hardenability.     

Influence of interrupted quenching on artificial aging of Al–Mg–Si alloys

In this study the influence of interrupted quenching (IQ) in the temperature range 150–250 °C for periods of 15–1080 s on artificial aging after long-term natural pre-aging was studied for the Al–Mg–Si alloy AA6061 by atom probe tomography, transmission electron microscopy, electrical resistivity and hardness measurements, and differential scanning calorimetry. Compared with a standard quenching procedure, the results showed that hardening kinetics and the age hardening response were enhanced for IQ at low temperatures but reduced at high temperatures. Quenched-in vacancies were shown to be of particular importance for the nucleation of precipitates occurring during IQ at the lower end of the temperature range, finally leading to the formation of a dense distribution of β″ during artificial aging. For standard water quenching and subsequent natural aging, nucleation is hindered by a low concentration of quenched-in vacancies in the matrix. IQ at high temperatures affects subsequent artificial aging via the formation of precipitates which do not contribute to hardening but consume a significant amount of solute.     

Improvement of product strength and formability in stamping of Al–Mg–Si alloy sheets having bake hardenability by resistance heat and artificial aging treatments

Resistance heat and artificial aging treatments were introduced into a stamping operation to improve the product strength and formability of Al–Mg–Si alloy sheets having bake hardenability used for automobile body panels. In this treatment, the sheets undergo re-solution by resistance heat treatment, composed of resistance heating and water quenching just before the stamping. Stamped sheets are artificially aged just after the stamping to increase product strength. In the experiment, Al–0.60% Si–0.74% Mg alloy sheets were chosen as an example of Al–Mg–Si alloy sheets having bake hardenability. The re-solution solution treatment of the sheets was sufficiently accomplished by rapid resistance heat treatment, and formability of the sheets was improved. Hardness of the formed products was increased by artificial aging. It was found that the present process is effective in improving the product strength and formability of Al–Mg–Si alloy sheets having bake hardenability due to the compactness and rapidness.     

时效时间对7150铝合金组织和性能的影响

通过维氏硬度测试、电导率测试和拉伸、晶间腐蚀等测试方法,研究了预时效、回归及再时效三个阶段中的时效时间对7150铝合金组织和性能的影响,借助透射电镜观察时效处理各阶段合金的微观组织演变。结果表明:120℃×20 h欠时效作为预时效工艺,比120℃×24 h峰时效的晶内析出相更细小,高温回归时更利于回溶。在190℃短时回归5、15和30 min中,15 min回溶效果最好,硬度最低,再经120℃×24 h再时效后合金抗拉强度Rm、屈服强度RP0.2、伸长率A分别为622 MPa、573 MPa、10.8%,显微硬度为204 HV,力学性能与120℃×24 h单级峰时效时相近。经120℃×20 h+190℃×15 min+120℃×24 h处理后7150铝合金综合性能好,耐晶间腐蚀性能佳。     

Interactive effects of aging parameters of AA6056

The effect of thermomechanical treatment on the aging behavior of AA6056 aluminum alloy was modeled using response surface methodology (RSM). Two models were developed to predict the final yield stress (FYS) and elongation amounts as well as the optimum conditions of aging process. These were done based on the interactive effects of applied thermomechanical parameters. The optimum condition predicted by the model to attain the maximum strength was pre-aging at 80 °C for 15 h, followed by 70% cold work and subsequent final aging at 165 °C for 4 h, which resulted in the FYS of about 480 MPa. As for the elongation, the optimum condition was pre-aging at 80 °C for 15 h, followed by 30% cold work and final-aging at 165 °C for 4 h, which led to 21% elongation. To verify the suggested optimum conditions, the tests were carried out confirming the high accuracy (above 94%) of the RSM technique as well as the developed models. It is shown that the RSM can be used successfully to optimize the aging process, to determine the significance of aging parameters and to model the combination effect of process variables on the aging behavior of AA6056.     

自然时效效应及预时效处理对7A20铝合金组织性能的影响

研究了中强度7A20铝合金的自然时效硬化效应及预时效处理对组织和性能的影响。采用光学显微镜和透射电镜表征了其微观组织结构,采用维氏硬度计和万能拉伸试验机测试了其硬度和力学性能。结果表明:固溶态7A20试验铝合金的自然时效硬化效应明显,12天后硬度由56 HV0.5提高到122 HV0.5,提高了117.86%。经120 ℃×10 min预时效处理后,自然时效硬化增量最低,相比于固溶态降低了16 HV0.5,有效抑制自然时效硬化效应;同时,预时效处理提升了烘烤硬化效应,烘烤硬化后屈服强度提升了166 MPa,抗拉强度提高了51 MPa,伸长率降低了7%。烘烤处理前,其晶内的强化主要来自于与基体共格的GP区,烘烤处理后为尺寸小于5 nm、弥散分布的η′强化相。     

Redistribution and re-precipitation of solute atom during retrogression and reaging of A1-Zn-Mg-Cu alloys

The redistribution and re-precipitation of solute atom during retrogression and reaging of three different A1-Zn-Mg-Cu aluminum alloys were investigated. The results of hardness and tensile strength test indicate that after pre-aging at 100 ℃ or 120 ℃ and retrogressing at 200 ℃ for various time and re-aging treatment, the hardness and strength of the alloys are all larger than those under pre-aging condition, some of them even exceed the value under peak aging（T6） condition. TEM observation shows that the PFZ formed during retrogressing in short time becomes narrow and even disappears after re-aging treatment. However, the PFZ formed during retrogressing for a long time does not narrow after re-aging treatment. It is suggested that the redistribution and re-precipitation of solute atom during re-aging treatment result in the narrowing and even disappearance of the PFZ formed during retrogression, which reinforces the grain-boundaries and presents the value of tensile strength exceeding peak-aging strength in the RRA condition, while the precipitates in the matrix of the alloys still keep or even exhibit a more dispersed distribution, and a greater effect of precipitation strengthening is obtained.     

Effect of step-quenching on microstructure of aluminum alloy 7055

The effect of step-quenching on the microstructure of aluminum alloy 7055 after artificial aging was studied by hardness testing and transmission electron microscopy (TEM). Step-quenching leads to decomposition of solid solution and heterogeneous precipitation of equilibrium phase mainly on dispersoids and at grain boundaries; thus lower hardness after aging. Prolonging isothermal holding at 415 ℃ results in coarser and more spaced η phase particles at grain boundaries with wider precipitates free zone, and lower density of larger η′ hardening precipitates inside grains after aging. Isothermal holding at 355 ℃ results in heterogeneous precipitation of η phase both on dispersoids and at grain boundaries. Isothermal holding at 235 ℃ results in heterogeneous precipitation of η phase first, and then S phase. Precipitates free zones are created around these coarse η and S phase particles after aging. Prolonging isothermal holding at these two temperatures leads to fewer η′ hardening precipitates inside grains, larger and more spaced η phase particles at grain boundaries and wider grain boundary precipitates free zone after aging.     

预时效对车身用6016铝合金烘烤硬化性能的影响

采用硬度测试、拉伸试验和透射电镜等手段研究了不同预时效处理对6016铝合金烘烤前后微观组织和力学性能的影响。结果表明:6016铝合金具有较强的自然时效硬化能力,自然时效24 h的6016铝硬度比固溶态合金硬度增加了45.6%。自然时效超过24 h以后,合金硬度值变化不大。通过预时效处理可以显著提高6016铝合金的烘烤硬化效果。经550 ℃×30 min固溶+160 ℃×10 min预时效处理后,6016铝合金规定塑性延伸强度为131.4 MPa,伸长率为24.7%。再经175 ℃×30 min烘烤后合金规定塑性延伸强度达到199.5 MPa,烘烤硬化值(BH)为68.1 MPa,此工艺为6016铝合金车身板最佳的热处理工艺。     

Pre-precipitate clusters and precipitation processes in Al–Mg–Si alloys

The solute clusters and the metastable precipitates in aged Al–Mg–Si alloys have been characterized by a three-dimensional atom probe (3DAP) and transmission electron microscopy (TEM). After long-term natural aging, Mg–Si co-clusters have been detected in addition to separate Si and Mg atom clusters. The particle density of β″ after 10 h artificial aging at 175°C varies depending on pre-aging conditions, i.e. pre-aging at 70°C increases the number density of the β″ precipitates, whereas natural aging reduces it. This suggests that the spherical GP zones formed at 70°C serve as nucleation sites for the β″ in the subsequent artificial aging, whereas co-clusters formed at room temperature do not. Atom probe analysis results have revealed that the Mg:Si ratios of the GP zones and the β″ precipitates in the alloy with excess amount of Si are 1:1, whereas those in the Al–Mg₂Si quasi-binary alloy are 2:1. Based on these results, the characteristic two-step age-hardening behavior in Al–Mg–Si alloys is discussed.     

AW-7075-T6 sheet for shock heat treatment forming process

The forming behaviour of AW-7075-T6 sheet was studied across a range of shock heat treatment (SHT) temperatures of 200-480 °C. After SHT, formability of the samples was investigated by tension and deep drawing tests at room temperature. Differential scanning calorimetry (DSC) was used to study the precipitation states of the AW-7075 sheet in the as-received and shock heat treated conditions. Formability was started to improve with increasing shock heat treatment temperature from 300 °C onwards. Strain hardening resulted from the dissolution of η′ precipitates and the coarsening of remaining precipitates were found to contribute to the increase in formability at room temperature. Re-precipitation and coarsening of the precipitates were responsible for the post-paint baking strength of SHT samples.     

冷加工和时效处理顺序对6061铝合金力学性能的影响(英文)

研究不同的析出硬化和冷加工组合对6061铝合金拉伸性能的影响。结果表明,在不同的热处理过程中,在180℃单时效4h能提高合金的强度和伸长率。然而,双时效处理不能改善其力学性能。另外,预时效对随后的析出硬化有负面影响。合金力学性能的变化归因于析出硬化、应变硬化和加工软化的竞争而引起的显微组织演变。     

Properties and Heat Treatment of High Transition Temperature Ni-Ti-Hf Alloys

The high transition temperature Ni-Ti (Hf, Zr) alloys have long been of interest for actuators and other applications requiring transition temperatures greater than 100 °C. Unfortunately, the high hardness and poor fabricability of these alloys have prohibited the scale up to commercial production. Some of these alloys are so “hot short” that even modest size ingots cannot be cast without internal cracks formed by solidification shrinkage stresses. Hot rolling methods have recently been demonstrated that can produce crack free Ni-Ti-(6-10 at.%)Hf thin sheets having austenite transition temperatures up to approximately 170 °C. Since these alloys are soft martensite phase at room temperature, they can easily be formed and bent at ambient temperature but cold rolling can only be performed to a limited extent due to high work hardening rates which are typical for Ni-Ti alloys. Progress is now underway to scale up these methods to produce 500-600 mm wide sheets. The effects of composition variations, heat treatment and cold working on transition temperatures are discussed. Microstructural features unique to these ternary alloys and impurity effects are also discussed. The effects of stress on transition temperature have been determined. Austenite transition temperatures, as measured by DSC and bend-free recovery testing, can be controlled within 100-170 °C for these alloys.     

6111铝合金的时效硬化研究

对6111铝合金的铸锭进行均匀化、热轧、退火、冷轧及固溶处理后,研究了其合金自然时效时及人工时效过程中硬度随时间的变化规律.研究表明,该合金具有一定的自然时效倾向,人工时效具有明显的回归现象.在人工时效前的预处理能明显增加人工时效时的硬化速度,提高烤漆硬化能力.