Ageing characteristics and microstructure of Al-4Mg-1.5Cu alloys containing silver and lithium

The ageing behavior and microstructures of the Al-4Mg-1.5Cu alloys containing silver and lithium have been studied. The results show that the effect of Li is to increase the rate of hardening, however, lithium additions in the range of 0 to 2.0% does not progressively change age hardening and precipitation process in the alloy of （Al-4.0Mg-1.5Cu-0.4Ag-0.12Zr） aged at 200 ℃, and significant age hardening and strengthening response only occur with the addition of 2.0%Li. TEM investigation results show that the remarkable increase of age hardness and strength is attributed to the fine dispersion of δ′, Z phase and spherical Al3Zr/Al3Li compound particles in the （2.0%Li-）containing alloy.

AGEING CHARACTERISTICS AND MICROSTRUCTURE OF Al-Mg-Li ALLOYS CONTAINING SMALL AMOUNT OF SILVER

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MECHANICAL PROPERTIES AND MICROSTRUCTURES OF Al-Mg-Li-Zr ALLOYS-CONTAINING SILVER

ＭＥＣＨＡＮＩＣＡＬＰＲＯＰＥＲＴＩＥＳＡＮＤＭＩＣＲＯＳＴＲＵＣＴＵＲＥＳＯＦＡｌ－Ｍｇ－Ｌｉ－ＺｒＡＬＬＯＹＳ－ＣＯＮＴＡＩＮＩＮＧＳＩＬＶＥＲ￥Ｚｈａｎｇ，Ｓｉｑｉ；Ｙｉｎ，Ｚｈｉｍｉｎ；Ｓｈｅｎ，Ｊｉａｎ；Ｌｕ，Ｂｉｎ；Ｌｉａｎｇ，Ｙｉｎｇ（...

Effects of Ag addition on the microstructures and properties of Al–Mg–Si–Cu alloys

Effects of Ag addition on the microsmactures, aging characteristics, tensile properties, electrochemical properties, and intergranu- lar corrosion （IGC） properties of Al 1.1Mg-0.8Si-0.9Cu-0.35Mn4）.02Ti alloy were investigated using scanning electronic microscopy and transmission electronic microscopy. The aging process of Al-Mg-Si-Cu alloys was accelerated by the addition of Ag. The strength of peak-aged Al-Mg-Si-Cu alloys was enhanced by Ag addition because of the high density of β＂- and L-phase age-hardening precipitates. The corrosion performance of the Al-Mg-Sii-Cu alloy is closely related to the aging conditions and is independent of the Ag content. The IGC susceptibility is serious in the peak-aged alloy because of the continuous distribution of Cu-rich Q-phase precipitates along grain boun- daries. Ag addition reduces the size of the grain-boundary-precipitate Q phase and the width of the precipitate-free zone and thus results in decreased IGC susceptibility of Al-Mg-Si Cu alloys.

MICROSTRUCTURE AND MECHANICAL BEHAVIOUR OF Al-Li-Zr AND Al-Li-Cu-Mg-Zr ALLOYS

The aging response,tensile and impact properties of two kinds of Al-Li based alloys have been studied.The microstructure,deformation as well as fracture behaviour in the alloys were observed with SEM and TEM.It was found that the mechanisms of deformation and fracture for different heat-treated alloys with the same chemical composition are quite different.The causes leading to the drop of ductility,toughness as well as anisotropy in peak-aged alloys have been analysed.Finally,possible methods to improve the ductility and toughness of the al- loys have been discussed.

Sc元素添加对双辊铸轧Al−Cu−Li−Mg−Zr基合金热处理的影响

提出制备含Sc的Al−Cu−Li−Mg−Zr基合金带材的工艺方案。即先采用双辊铸轧技术制备近净形状的3 mm厚带材,再对其进行均匀化/固溶处理。研究两种Al−Cu−Li−Mg−Zr基双辊铸轧合金,其中一种添加质量分数为0.17%的Sc,另一种未添加Sc。两种合金均先在300℃下退火30 min,然后在450℃下退火30 min以及530℃下退火30 min,随后进行室温水淬。前两段退火后组织中生成了细小、弥散的Al_(3)Zr/Al_(3)(Sc,Zr)颗粒。最后的退火步骤起到了均匀化/固溶处理的作用。双辊铸轧材料的细小晶粒结构使含有主要合金元素的原始颗粒在较短的退火时间内溶解。缩短保温时间可以限制表面层中Li的耗尽和Al_(3)Zr/Al_(3)(Sc,Zr)弥散相的明显粗化。铸态含Sc材料已经具有明显细小的晶粒结构,而经均匀化/固溶处理后生成的Al_(3)(Sc,Zr)弥散相抑制了晶粒在高温下发生粗化。在后续180℃下时效处理后,形成了θʹ(Al_(2)Cu)、T1(Al_(2)CuLi)和S'(Al_(2)CuMg)强化相。在峰值时效状态下,屈服强度提高了200 MPa,这一数值与类似直接冷却铸造材料的相当,从而证实了所提方案的合理性。

EFFECTS OF SMALL ADDITIONS OF Mg AND Ag ON PRECIPITATION PROCESS OF Al-Cu-Li-(Mg)-(Ag)-Zr ALLOYS

１ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｔｅｒｎａｒｙＡｌＣｕＭｇａｌｏｙｓｗｉｔｈｈｉｇｈＣｕ∶Ｍｇｍａｓｓｒａｔｉｏｓ，ｓｍａｌａｄｄｉｔｉｏｎｓｏｆＭｇｐｒｏｍｏｔｅｔｈｅｐｒｅｃｉｐｉｔａｔｉｏｎｏｆｓｔｒｅｎｇｔｈｅｎｉｎｇｐｈａｓｅｓｗｈｉｃｈ...

Effect of aging in an electric field on microstructures and properties of 1420 Al-Li alloy

After solution treatment, the 1420 Al-Li alloy samples were aged at different temperatures in an electric field with different intensity. The measurements made showed that the electric field increased the strength of the 1420 Al-Li alloy, and best properties were obtained when they were aged at 120 ℃ with E=4 kV/cm for 12 hrs. The electric field promoted the nucleation of δ′ phase, increased the quantity of the δ′ phase, and made the size of the δ′ phase particles smaller. The electric field restrained the formation and growth of PFZ, and increased the intensity of the electric field while the width of the PFZ was decreased.

Creep ageing behaviour assisted by electropulsing under different stresses for Al−Cu−Li alloy

The influence of electropulsing on the creep behaviour,strength,and microstructure of an Al−Cu−Li alloy during creep ageing was investigated.Electropulsing assisted creep ageing(ECA)and conventional creep ageing(CCA)were carried out under various stress levels and time conditions.Applying electropulsing results in a noteworthy change of creep behaviour,including a variation in creep curves,an increased creep rate in early stage,and an improved creep strain.The ECA specimen experiences a shorter time to the peak strength,and an increase in elongation by~17.4% without loss of the peak-aged strength compared with CCA specimen.The ultrafine nano-size subgrains are observed to form under electropulsing,which can result in an increased creep strain by increasing grain-boundary sliding.The enhancement of both dislocation interactions and solute diffusion under electropulsing is considered as a primary cause of disappearance of a platform stage during early creep ageing.Some of T1 precipitates around the grain boundary are observed in the peak ECA sample,resulting in an occurrence of transgranular fracture,which is further responsible for an increased elongation of the ECA specimen.

Effects of RRA Treatments on Microstructures and Properties of a New High-strength Aluminum-Lithium Alloy-2A97

A new high strength 2A97 Al-Cu-Li-X alloy was subjected to triple-aging of retrogression and re-aging treatments （RRA）. Transmission electron microscopy （TEM）, differential scanning calorimetry （DSC）, and tensile tests were used to investigate the effects of RRA treatment on the microstructures and properties. DSC test reveals the reversion temperature range of the strengthening δ＇ （Al3Li） phase. The results show that the microstructure consists of δ＇ （Al3Li） phase, T1 （Al2CuLi） phase and θ″/θ′（Al2Cu） phase for 2A97 alloy treated by a triple-aging of a retrogression and re-aging treatment in the following order： （1） at 165℃×30 min, （2） at 220 ℃ or 240℃ × 15 min, （3） at 165℃×24 h. The plastic deformation, incorporated into the treatment after secondary high temperature aging, promotes the T1 precipitation during final re-aging. The tensile properties of the alloy treated by the retrogression and re-aging treatment reach the peak level of alloy single-aged at 165℃ in T6 temper.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 8090 Al-Li ALLOY

The change of mechanical properties of the 8090 Al-Li alloy influenced by aging is attributed to the change of δ′-phase particle size and the precipitation of S′-phase.The δ′-phase may easily precipitate and rapidly grow,but the S′-phase can only precipitate with a longer stage of incubation.The precipitation of S′-phase would be promoted by cold working prior to ag- ing.The co-precipitation of δ′- and S′-phase could improve the strength and plastieity of the alloy,for which aging at 190℃.for 20—30 h seems to be optimal.In addition,the precipitate free zone( PFZ)can form at high angle grain boundary and its width is over 200 nm in peak aging condition.But at sub-grain boundary,the formation of PFZ is difficult.

微量Ag,Mg对Al-Cu-Li合金时效特性和显微组织的影响

研究了微量Ag,Mg对Al-Cu-Li合金显微组织和时效特性的影响。结果表明:单独加Ag对Al-Cu-Li系2197合金的固溶强化效果很小,但有较强的时效强化作用,Ag含量不同,时效强化效果也不同;Ag,Mg共同加入提高了T1相(Al2CuLi)的析出速率和析出密度,使合金具有较大的固溶强化效果及最强烈的时效响应和时效强化效果。Ag,Mg的添加对合金的不同影响可通过溶质原子与空位、溶质原子与溶质原子之间的相互作用来解释。

微量Ag对Al-Mg-Li-Zr合金时效特性和微观组织的影响

研究了添加微量银对Ａｌ－Ｍｇ－Ｌｉ－Ｚｒ合金的机械性能和时效组织的影响，通过对时效硬度、拉伸强度、延伸率的测试以及Ｘ射线衍射与ＴＥＭ观察表明，微量银的加入可使Ａｌ－Ｍｇ－Ｌｉ－Ｚｒ合金得到显著硬化和强化，同时推迟了时效峰值的显现；银的含量越大，合金的过时效越缓慢；在Ａｌ－Ｍｇ－Ｌｉ合金中加入质量分数为０．５２％的银可生成Ｔ相；同时微量银的加入，抑制了δ＇相的长大．

微量Mg,Ag对Al-Li-Cu系合金性能和组织的影响

在ＡＡ２１９５标准成分基础上，通过加入微量元素Ｍｇ和Ａｇ，研究了各合金薄板材料在１８０℃不同时效时间下的室温拉伸性能和显微组织特征，实验结果表明：单独加入Ｍｇ和单独加入Ａｇ对ＡｌＬｉ合金都有强化效果，但Ｍｇ的单独作用显然比Ａｇ要大得多．Ｍｇ和Ａｇ共同加入则产生最大的强化效应，这说明Ｍｇ和Ａｇ之间有强烈相互作用．

非等温时效对含银Al-Mg-Si合金多层摩擦表面显微组织和腐蚀行为的影响

研究非等温时效对添加不同银含量Al-Mg-Si合金多层摩擦表面显微组织和腐蚀行为的影响。通过在耗材棒横截面上钻孔的方式添加4%、8%和13%(质量分数)的银。采用光学显微镜和电子显微镜研究涂层的显微组织,采用显微硬度和拉伸实验研究涂层的力学性能,采用电化学测试研究样品的耐腐蚀性。结果表明,随着银添加量从4%(质量分数)增加到13%(质量分数),摩擦堆焊表面层的晶粒尺寸从(1.5±0.3)μm减小到(1.0±0.3)μm。铝基体中的溶质银能够加速Al-Mg-Si合金的析出动力学。经非等温时效处理后,含银涂层的屈服强度和抗拉强度分别比不含银涂层高50.6%和43.5%。经非等温时效处理后,材料的腐蚀电流密度降低,含银和不含银样品的耐腐蚀性均提高,含银涂层的耐蚀性比无银镀层提高了96.5%。

添加少量Ag对Al-Li合金时效硬化行为的影响

本文通过硬度测量、拉伸实验以及透射电镜观察研究了添加0.5%Ag对一种Al-Li-Cu-Mg-Zr合金时效硬化的影响。结果表明,添加Ag对δ′相的析出无明显影响,但促进了T相的析出。在单级时效或双级时效时,Ag明显增加实验合金的时效硬化效果,时效前的预变形减少了Ag对时效硬化的影响。含Ag合金经低温预时效后再在较高温度时效的初期阶段,出现性能下降的回归现象。

Effect of aging on the mechanical properties and corrosion susceptibility of an Al-Cu-Li-Zr alloy containing Sc

The effects of aging on the microstructure, mechanical properties, intergranular corrosion, and exfoliation corrosion of an Al-3.5Cu-1.5Li-0.22（Sc ＋ Zr） alloy have been investigated. The results show that the alloy has the character of age hardening, and the major phase of precipitation and strengthening is the T1 phase. The aging temperature and aging time have a significant effect on the amount and distribution of the T1 phase. The proper artificial single-aging treatment of the alloy is at 160℃ for 40 h. The intergranular corrosion and exfoliation corrosion of the alloy are caused by the anodic dissolution of the T1 phase and the precipitate-free zone （PFZ）. With increasing the aging time to overaged, the T1 phase coarsens, and the PFZ widens, leading to an increase in the susceptibility to intergranular corrosion and exfoliation corrosion.

Aging behaviors of Al-Cu-Li-Zr alloy containing Sc

Single aging effects on the microstructures and the room-temperature mechanical properties of Al-3.5Cu-1.5Li-0.22（Sc+Zr） alloy were observed using TEM, tensile test and hardness test at room temperature. The results show that the alloy has the character of aging hardening. The aging temperature and aging time have significant effects on the amount and distribution of the major phase of precipitation and strengthening of the alloy. At both high and low temperatures, the precipitation caused by aging is few and coarse, but at high temperature, the coarse equilibrium phases are visible at grain boundaries, therefore, influencing the composite properties of the alloy. The proper artificial single-aging treatment of the alloy is 160℃, 40h. Under this condition, the alloy obtains homogeneously distributed fine T1 phases, which leads to an optimal mechanical properties, i.e. σb is 483MPa, σ 0.2 is 413MPa, and δ is 8.4% for the alloy. However, extending overaging to 50h at 160℃, the coarse equilibrium phases precipitate at grain boundaries leads to wide precipitates-free zone（PFZ） along the grain boundaries, further results in a decrease in the composite properties of the alloy.

Zn对Al-Li-Cu-Mg-Zr合金时效过程的影响

Zn的存在加快了Al-Li-Cu-Mg-Zr合金的时效硬化速度,明显促进S’相的析出,降低δ’颗粒的长大速度.经过长时间时效后,含Zn合金中将析出含Zn的条状相;根据正电子湮没参数的变化研究了时效过程中Zn对合金的缺陷浓度及基体电子结构的影响.

分级时效对新型Al-Cu-Li合金组织与性能的影响

通过力学性能和显微组织检测分析,研究了分级时效工艺对新型Al-Cu-Li合金组织与性能的影响。结果表明:经先高温后低温的双级时效处理和先低温后高温再低温的三级时效工艺处理的合金强度均比T6态的高,但比T8态的稍低;对于先高温后低温的双级时效制度,合金在165℃高温时效析出了δ′、θ′、T1相和σ相,然后,在130℃二次时效后析出大量细小弥散针状强化相,从而提高了合金的强度;对于先低温后高温再低温的三级时效工艺制度,在150℃预时效形成GP区和过渡相,从而在165℃时效析出了较多的第二相,经130℃的第三级时效后析出了细小的第二相,从而使合金具有较好的综合力学性能。