几种时效硬化铝合金在峰值时效条件下的拉伸行为

本文对几种工业常用的时效硬化铝合金和新研制的Al-Li系合金8090的拉伸性能和断口进行了研究和比较。结果表明,在峰值时效条件下,Al-Li系合金显示出较高的沿晶开裂倾向,而其它常用的时效硬化铝合金,无论拉伸性能如何,均发生韧窝型开裂。Al-Li系合金高的沿晶开裂倾向是由该合金较高的时效沿晶析出现象所决定的。     

含Sc铝合金的应用研究新进展与前景展望

含Sc铝合金强度高、热稳定性好,有强烈的时效硬化效应。Sc是发展高强度、高耐热性和高抗蚀性铝合金的一种高效的微量添加元素,但Al-Sc中间合金的昂贵价格严重制约了含Sc铝合金的应用。简要介绍了国内外含Sc铝合金应用研究的最新进展,提出了降低Al-Sc中间合金制备成本的有效途径,并展望了含Sc铝合金应用研究的发展方向。     

7xxx系铝合金回归再时效的研究现状

7xxx系铝合金作为高强度铝合金的代表,以其较高的强度以及良好的韧性和耐蚀性等优异性能而广泛地应用于航空航天及交通运输领域.该类可热处理强化铝合金对微观组织结构敏感,其性能受合金内部析出相的形核、生长及分布情况的影响.采用三级时效工艺—回归再时效处理,通过预时效、回归、再时效3个过程的有效配合改变合金的析出相状态,可以...     

添加Fe对Cu-9Ni-6Sn合金时效硬化的影响

文章对真空熔铸含Fe量为 0 .37wt%～ 1 .36wt%的Cu 9Ni 6Sn合金的时效硬化、形变时效硬化过程及其组织变化作了研究 .实验证明 :0 .37wt%～ 1 .37wt?能完全固溶于Cu 9Ni 6Sn合金中 ;含少量Fe的合金的时效硬化、形变时效硬化及其组织变化的基本特征与不含Fe的Cu 9Ni 6Sn合金相类似 ,但少量Fe促进合金时效、形变时效过程 ,增加硬化效果 .     

预时效对6061、6005A合金板材力学性能的影响

通过对不同预时效制度下的6061和6005A合金板材进行力学性能、延伸率、加工硬化率、电导率、组织检测等试验,研究了预时效对汽车板材成形性能和烤漆硬化性能的影响。结果表明,180℃×5 min的预时效制度可改善6061-T4和6005A-T4合金板材成形性。热处理状态为T4P+T6的6061和6005A的强度均明显高于T4+T6态。这说明预时效可以解决铝合金板材因自然时效引起的人工时效强化效果不佳的问题,有利于汽车板材的冲压成形和烤漆硬化能力的提高。     

时效处理对7075铝合金组织和性能的影响

对7075铝合金进行了单级时效处理和双级时效处理，表征了微观组织，测试了显微硬度。利用电化学工作站测试了腐蚀性能。实验结果表明：7075铝合金经120℃时效24h后，平均硬度为196HV；二级时效温度为160℃时，随时效时间的延长，硬度值基本呈现逐渐降低的趋势。7075铝合金经一级时效处理后，第二相析出产生时效硬化效果；在较高温度下进行二级时效，随保温时间的延长，时效析出相发生聚集、粗化和长大，降低了合金的硬度。随着二级时效时间的增长，合金的腐蚀电流先升高后降低，在二级时效16h、24h时合金的腐蚀电流最小，腐蚀性能最优。     

双级时效对7075铝合金力学性能的影响

本文研究了7075铝合金固溶处理后双级时效热处理工艺,分析了双级时效工艺对7075铝合金力学性能的影响.合金成份一定的7075铝合金挤压型材,经470℃2h固溶后,再经120℃×6h+165℃x5h双级时效时能获得较好的综合性能,为7075铝合金时效热处理工艺参数的确定及优化提供参考依据.     

少量Mn对Cu－15Ni－8Sn合金时效硬化的影响

本文对真空熔铸含Ｍｎ量为０．４６ｗｔ％的Ｃｕ－１５Ｎｉ－８Ｓｎ合金的时效硬化、形变时效使化过程及其组织变化作了研究。实验证明：（１）０．４６ｗｔ％Ｍｎ固溶于Ｃｕ－１５Ｎｉ－８Ｓｎ合金中，（２）含少量Ｍｎ的合金的时效硬化、形变时效硬化及组织变化的基本特征与不含Ｍｎ的Ｇｕ－１５Ｎｉ－８Ｓｎ合金相类似，但少量Ｍｎ延缓合金的时效、形变时效过程，增加硬化效果。     

添加Mn对Cu－9Ni－6Sn合金组织与性能的影响

作者对含０．４６—１．０６ｗｔ％Ｍｎ的Ｃｕ－９Ｎｉ－６Ｓｎ合金的铸造组织、时效和形变时效特征及组织交化、时效合金的耐蚀性变化作了研完。实验证明，合金的铸锭组织、时效硬化、形变时效和组织变化等基本特征与不含Ｍｎ的合金相类似。添加０．４６ｗｔ％Ｍｎ延缓了合金时效和形变时效近程，添加０．７４—１．０６ｗｔ％Ｍｎ加速了合金时效和形变时效近程，但都升高了最佳时效温度，增加了硬化效果和在酸中的耐蚀性。     

Al-Mg-Si-Cu系铝合金晶间腐蚀研究进展

简述了铝合金晶间腐蚀机理,以及合金元素对Al-Mg-Si-Cu系铝合金晶间腐蚀性能的影响。主要介绍了合金元素、时效热处理等对Al-Mg-Si-Cu系铝合金晶间腐蚀敏感性的影响。大量研究表明,合金晶间腐蚀向点蚀的转变与均匀化热处理、固溶温度、冷却速率以及人工时效等因素有关,经合适的热处理后Al-Mg-Si-Cu系铝合金可由晶间腐蚀转变为轻微点蚀。同时,展望了Al-Mg-Si-Cu系铝合金晶间腐蚀研究的发展方向。     

Age Hardening Behavior and Corresponding Microstructure of Dilute Al-Er-Zr Alloys

The age hardening and the microstructure of dilute Al-Er-Zr alloys were investigated by microhardness tests and TEM. The Al-0.04Er alloy shows a conventional age hardening behavior and obtains a maximum hardness of 410 MPa after aging for 2 h at 523 K (250 °C) due to precipitation of Al₃Er. The addition of Zr to Al-Er alloy can slow down the growth of the precipitates and make the age hardening effect remain for a long time in Al-0.04Er-0.04Zr alloy. Addition of Zr retards the decomposition of Al-Er and the Al-0.04Er-0.08Zr alloy can reach higher peak hardness than that of Al-0.04Er after aging for long time at elevated temperature. The precipitation behavior of Al-Er-Zr system is likely to be a new commercial way to developing creep-resistant aluminum alloy.     

Effects of oxygen and heat treatment on the mechanical properties of alpha and beta titanium alloys

Two alloys, Ti-6Al-2V and Ti-2Al-16V, simulating the alpha and beta phases of Ti-6A1-4V, respectively, were prepared with oxygen concentrations from 0.07 to 0.65 wt pct (0.20 to 1.83 at. pct). Their microstructure, deformation behavior, and strength were investigated with X-ray diffraction, microscopy, and mechanical tests to determine the effects of oxygen concentration and heat treatment. In both alloys the hardness increases in identical fashion with the square root of oxygen concentration. The alloys' strengths also depend on heat treatment, but in different ways. Whereas the alpha alloy is non-age-hardenable, the beta alloy's strength can be doubled by aging. The hardening effect of oxygen is generally unaffected by heat treatment, except for the alloys with the highest oxygen concentrations. During aging of the alpha a small amount of Ti₃Al can form, and slight age-hardening occurs. The ductility of the alpha alloy is little affected by aging. On the other hand, oxygen causes a change from good ductility at low oxygen concentration (0.07 wt pct) to total brittleness at 0.65 wt pct oxygen, independent of heat treatment. In the beta alloy there are complex phase transformations depending on heat treatment. Its deformation behavior varies from very ductile in solutiontreated and quenched (STQ) condition to totally brittle in aged conditions. The aging embrittlement appears to be caused by alpha and some omega precipitation. Decoration of the beta grain boundaries with precipitates accounts for the intergranular brittle fracture. Oxygen, on the other hand, is not an embrittler, although it reduces the ductility of the beta alloy.     

The effect of prior deformation on spinodal age hardening in Cu-15 Ni-8 Sn alloy

The structure and kinetics of aged Cu-15 Ni-8 Sn with and without prior deformation was investigated by means of X-ray diffraction and transmission electron microscopy. Deformation prior to aging is known to accelerate the hardening process in this alloy. The purpose of the study was to determine whether the strengthing mechanisms are kinetically enhanced through modified alloy decomposition or through other mechanisms. Deformation does not affect most of the features of structure development, including DO₂₂ ordering in the tin-rich phase. However, for a given aging treatment, cold worked material shows a reduced strain modulation. The accelerated strengthening response in cold worked alloys cannot be attributed to an accelerated or altered decomposition process. It is suggested that the coarsened spinodal structure and the dislocation structure interact in a synergistic way to give the observed strengthening acceleration.     

Hundred years of precipitation hardening

About 100 years ago, precipitation hardening was discovered and the first structural aluminum alloys with considerable strength were developed. Our present understanding of the phenomenon in based on the application of dislocation theory as well as reaction kinetics, especially the role of metastable phases and lattice defects in nucleation from supersaturated solids. The prerequisites for optimum precipitation hardening can be precisely defined. However, the progress in the development of new alloys has been slow in the recent years. The original alloy is still in use today.     

Aging kinetics of aluminum alloy 7050

Precipitation hardening at room temperature (natural aging) and isothermal precipitation hardening at 422 to 455 K beyond the point of peak strength (overaging) were studied. Natural aging kinetics of the increase in strength and resistivity were comparable with those of alloy 7075. Alloy 7050, however, develops peak strength by aging at higher temperatures. This ability of 7050 to develop peak strength upon aging in the temperature region used to improve the resistance to stress-corrosion cracking and toughness of 7XXX alloys is attributed to the effect of Cu on increasing the temperature range of G.P zone stability.     

High-strength Cu-Ni-Sn alloys by thermomechanical processing

The influence of prior cold work on the aging characteristics and mechanical properties response for copper-rich alloys in the Cu-Ni-Sn system has been investigated. It has been established^15,16 that there exists a spinodal mode of decomposition below a critical temperatureT _R, 200 to 300°C below the equilibrium phase boundary in this system. Significant age hardening response is observed in this region; however, fracture ductility is severely impaired due to a grain boundary precipitate network which develops after relatively short aging times. Cold work prior to low temperature aging is found to have relatively little influence on the incubation time for this embrittling network. It does, however, profoundly enhance the kinetics of the continuous (spinodal) transformation. It is observed that for broad variations in composition, critical combinations of prior cold work, aging time and temperature yield material with unique combinations of. yield stress and fracture ductility (for example, a Cu-9 wt pct Ni-6 wt pct Sn alloy may be processed to exhibit an 0.01 pct offset yield of 174,000 psi in conjunction with a 55 pct R.A. on fracture; significantly higher 0.01 pct offset yield values may be achieved at some reduction in fracture ductility for other NiJSn ratios). It is concluded that the resultant ductileJbrittle properties response is a consequence of a critical compctitive balance between amplitude development in the modulated structure and nucleation of the grain boundary network. The minimum level of prior cold work required to effect this balance in the Cu-9 wt pct Ni-6 wt pct Sn alloy is 75 pct R.A. The present levels of yield stressJfracture ductility values reported, to the best of our knowledge, are unsurpassed by those of any other copper-base alloy system (at a significant cost reduction to the Cu-Be alloys) and suggest the potential yet to be realized in other systems exhibiting this mode of decomposition.     

High-strength Cu-Ni-Sn alloys by thermomechanical processing

The influence of prior cold work on the aging characteristics and mechanical properties response for copper-rich alloys in the Cu-Ni-Sn system has been investigated. It has been established^15,16 that there exists a spinodal mode of decomposition below a critical temperatureT _R, 200 to 300°C below the equilibrium phase boundary in this system. Significant age hardening response is observed in this region; however, fracture ductility is severely impaired due to a grain boundary precipitate network which develops after relatively short aging times. Cold work prior to low temperature aging is found to have relatively little influence on the incubation time for this embrittling network. It does, however, profoundly enhance the kinetics of the continuous (spinodal) transformation. It is observed that for broad variations in composition, critical combinations of prior cold work, aging time and temperature yield material with unique combinations of. yield stress and fracture ductility (for example, a Cu-9 wt pct Ni-6 wt pct Sn alloy may be processed to exhibit an 0.01 pct offset yield of 174,000 psi in conjunction with a 55 pct R.A. on fracture; significantly higher 0.01 pct offset yield values may be achieved at some reduction in fracture ductility for other NiJSn ratios). It is concluded that the resultant ductileJbrittle properties response is a consequence of a critical compctitive balance between amplitude development in the modulated structure and nucleation of the grain boundary network. The minimum level of prior cold work required to effect this balance in the Cu-9 wt pct Ni-6 wt pct Sn alloy is 75 pct R.A. The present levels of yield stressJfracture ductility values reported, to the best of our knowledge, are unsurpassed by those of any other copper-base alloy system (at a significant cost reduction to the Cu-Be alloys) and suggest the potential yet to be realized in other systems exhibiting this mode of decomposition.     

Precipitation of carbides in deformed vanadium

Strain aging measurements on alloys of vanadium with 0.3 at. pct carbon have been carried out over the temperature range 200°C to 500°C. The multiplicity of hardening stages char-acteristic of quench aging in this alloy is not altered by deformation. This behavior is in-terpreted as evidence that carbides nucleate in such profusion through the bulk of the metal that dislocations do not contribute an appreciable fraction of additional nucleation sites (even after 40 pct deformation). Only in the final stages of hardening does deformation in-fluence the kinetics of the process.     

Deformation and fracture behavior of two Al-Mg-Si alloys

Deformation and fracture behavior of two Al-Mg-Si alloys in different aging conditions has been studied by tensile testing, transmission electron microscope (TEM), and scanning electron microscope (SEM) observation. Tensile test results show that the strain hardening exponents (n values) of the two alloys decrease sharply at the early stage of artificial aging and are only 0.045 and 0.06, respectively, in the overaged condition. The sharp decrease of work hardening rate is believed to be one major reason that results in the rapid decrease of elongation to failure at the early stage of artificial aging. In fully aged conditions, dislocations are concentrated in narrow bands during plastic deformation of these alloys, which is responsible for the very low n values of the Al-Mg-Si alloys in peak aged and overaged conditions. The Si particles formed in the interior of grains of the higher Si containing alloy reduce the inhomogeneous deformation behavior. The TEM results show that large precipitates and precipitate-free zones (PFZs) along grain boundaries are formed in peak aged and overaged conditions, and SEM observations demonstrate that the tensile fracture modes of the two alloys in these aging conditions are completely intergranular with many small cusps decorated on facets of the fractured grain boundaries. Thus, the fracture process of both alloys is suggested to be that in which the high local stresses, built up where the slip band impinges on the grain boundaries, nucleate voids at the grain boundary precipitates by decohesion of the particle/PFZ interface, and then coalescence of these voids within the PFZ leads to the final fracture of these alloys.