Effect of aging on mechanical properties and localized corrosion behaviors of Al-Cu-Li alloy

The effects of aging on mechanical properties,intergranular corrosion and exfoliation corrosion behaviors of a 2197 type A1-Li alloy were investigated,and the mechanisms were studied through microstructure observation and electrochemical measurement of simulated bulk phase.The main strengthening precipitates of the alloy aged at175 ℃ and 160 ℃ are δ' and T1.T1 precipitation in the alloy aged at 160 ℃ is delayed,which results in its slower age strengthening and over-aging behavior than the alloy aged at 175 ℃.Meanwhile,aging temperature of 160 ℃causes more uniform distribution and finer size of T1,resulting in its better strengthening effect.As aging time and aging temperature are increased,the size of T1 at grain boundaries and the width of PFZ along grain boundaries are increased,leading to an increase in the susceptibility to intergranular corrosion and exfoliation corrosion.It is suggested that better comprehensive properties can be obtained when the alloy is aged at 160 ℃.     

非等温时效对一种铝锂合金力学性能与微观组织的影响

比较研究了一种Mg、Ag、Zn多元复合微合金化铝锂合金等温T8时效及非等温(降温)T8时效时的微观组织与力学性能。结果表明,该铝锂合金主要时效强化相为T1相(Al_2Cu Li),同时还存在θ相(Al_2Cu)及δ相(Al_3Li)的补充强化作用。相比于等温T8时效而言,降温T8时效可在不降低延伸率的同时,提高铝锂合金的强度。另外,降温T8时效时T1相析出及生长速度较慢,而且峰时效时θ相及δ相含量较高,补充强化作用更大。     

2050铝锂合金薄板拉伸性能及晶间腐蚀与时效的相关性

采用拉伸性能测试、浸泡腐蚀及透射电镜(TEM)观察,研究了 2050铝锂合金薄板T6及T8态时效时后的拉伸性能、晶间腐蚀(IGC)及微观组织.结果表明,T8态时效2050铝锂合金强度及伸长率均明显高于T6态时效.T6及T8态时效时,合金IGC敏感性随时效延长至峰时效阶段而逐渐降低;进一步延长至过时效阶段,IGC敏感性有...     

时效对2195铝锂合金腐蚀行为的影响

研究了2195铝锂合金在不同时效状态下的晶间腐蚀和剥落腐蚀行为.结果表明:2195合金在自然时效状态下具有较好的抗晶间腐蚀和剥落腐蚀能力,但随着在160℃时效时间的延长,其晶间腐蚀与剥落腐蚀倾向逐渐增加;在剥落腐蚀溶液中进行的极化曲线测试也表现出相同的趋势.透射电镜观察发现:2195合金主要析出相为T1相;随着时效时间延长,T1相逐渐粗化,在晶界处还会出现无析出带及平衡相.模拟相实验证实,由于T1相和无析出带的开路电位都明显低于铝基体的,在腐蚀性介质中作为阳极相优先溶解,从而导致2195合金产生晶间腐蚀及剥落腐蚀.过时效状态与峰时效状态相比,晶界平衡相增多,无析出带变宽,晶间腐蚀及剥落腐蚀程度将更加严重.     

含钪Al-Cu-Li-Zr合金的热处理制度

通过显微组织观察和室温拉伸实验,研究了固溶热处理制度和时效制度对含Sc的Al-Cu-Li-Zr合金拉伸力学性能与显微组织的影响。结果表明,适当提高固溶温度或延长固溶时间可以促进合金中过剩相的溶解,提高合金的强度和塑性;合金适宜的固溶-时效处理制度为530℃×1 h水淬＋160℃×40 h时效,在此条件下,合金的抗拉强度、屈服强度和伸长率分别为490MPa、416 MPa和9.8%。T1相是合金的主要时效强化相。     

时效处理对挤压成型2195铝锂合金组织和力学性能的影响

研究了热处理对挤压态2195铝锂合金组织和力学性能的影响。结果表明,固溶处理和人工时效处理对挤压合金的力学性能有显著的增强作用,这与析出相的类型、尺寸、数量密度和分布有关。2195铝锂合金在时效过程中的析出顺序为过饱和固溶体(SSSS)→GP区+δ′/β′(Al₃(Li,Zr))→δ′+θ′(Al₂Cu) +T₁ (Al₂CuLi)→θ′+T₁;其中T₁相在析出强化中起主导作用。2195铝锂合金经过525 ℃×60 min固溶后在170 ℃人工时效的峰时效时间是36 h,此时抗拉强度、屈服强度和伸长率分别为579 MPa、537 MPa和5.5%。     

微量Sc对2195铝锂合金应变时效态的显微组织和力学性能的影响

采用拉伸试验机、光学金相显微镜、透射电镜、扫描电镜等设备研究了添加微量Sc对2195铝锂合金应变时效态的显微组织和拉伸性能的影响。结果表明：微量Sc加入后能生成细小弥散Al3(Sc，Zr)质点，起到抑制再结晶的作用；微量Sc的加入既促使合金晶内析出的T1相分布更弥散均匀，又能使亚晶界和晶界上析出的T1相变得细小，几乎不出现明显的晶界无析出带，因而可在不降低合金强度的前提下有效地改善其塑性。     

双级蠕变时效对含钪7050铝合金力学及耐腐蚀性能的影响

研究了双级蠕变时效对含钪7050合金力学性能和耐腐蚀性能的影响,并与单级蠕变时效和无应力双级时效的试验结果进行了比较。结果表明,与单级蠕变时效相比,双级蠕变时效可明显提高含钪7050合金的力学性能;经单级或双级蠕变时效处理的合金比无应力双级时效合金具有更好的耐蚀性,而单级蠕变时效合金的耐蚀性优于双级蠕变时效合金。此外,压应力状态下的单级或双级蠕变时效合金比拉应力状态下的单级或双级蠕变时效合金具有稍高的硬度和耐蚀性。     

强化固溶处理对含锶钪7085铝合金腐蚀性能的影响

采用硬度和电导率测试、晶间腐蚀和剥落腐蚀试验、光学金相电镜观察,研究强化固溶处理对含锶钪7085型铝合金(Al-8.34Zn-1.89Mg-1.83Cu-0.15Zr-0.060Sr-0.10Sc)硬度、电导率、晶间腐蚀和剥落腐蚀性能的影响。结果表明,与常规固溶(470℃×2 h)处理相比,强化固溶(470℃×2 h+480℃×2 h+490℃×2 h)处理使合金中粗大析出相溶解更为充分,晶粒(亚晶粒)等轴性显著提高。经强化固溶处理加传统T6(121℃×24 h)处理后合金的硬度提高、电导率略有降低,抗晶间腐蚀和剥落腐蚀性能显著提高。     

预拉伸变形量对2050铝锂合金组织和性能的影响

通过拉伸试验、晶间腐蚀试验以及透射电镜(TEM)等方法对固溶处理后不同预拉伸变形量处理并人工时效后2050铝锂合金厚板室温拉伸性能、抗晶间腐蚀性能以及合金的微观组织形貌进行了研究。结果表明,随预拉伸变形量的增加,合金L向和LT向的屈服强度和抗拉强度逐渐增大,变形量＞4.0%后趋于平稳,伸长率逐渐降低后趋于稳定;随预拉伸变形量增加,腐蚀形貌由晶间腐蚀变为点蚀,点蚀深度逐渐减小。预拉伸变形促进了人工时效过程中晶内T₁相的弥散析出,降低了晶界处T₁相含量,因此提高了合金的强度和抗晶间腐蚀性能。预拉伸变形量为5.0%时,合金的强度和抗晶间腐蚀性能最佳。     

Effect of ageing treatment on microstructures,mechanical properties and corrosion behavior of Mg-Zn-RE-Zr alloy micro-alloyed with Ca and Sr

Effects of ageing treatment on the microstructures, mechanical properties and corrosion behavior of the Mg-4.2Zn-1.7RE-0.8Zr-xCa-ySr [x=0, 0.2 (wt.%), y=0, 0.1, 0.2, 0.4 (wt.%)] alloys were investigated. Results showed that Ca or/and Sr additions promoted the precipitation hardening behavior of Mg-4.2Zn-1.7RE-0.8Zr alloy and shortened the time to reaching peak hardness from 13 h to 12 h. The maximum hardness of 77.1±0.6 HV for the peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy was obtained. The microstructures of peak-aged alloys mainly consist of α-Mg phase, Mg₅₁Zn₂₀ phase and ternary T-phase. The Zn-Zr phase is formed within the α-Mg matrix, and the Mg₂Ca phase is formed near T-phase due to the enrichment of Ca in front of the solid-liquid interface. Furthermore, fine short rod-shaped β′₁ phase is precipitated within the α-Mg matrix in the peak-aged condition. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy exhibits optimal mechanical properties with an ultimate tensile strength of 208 MPa, yield strength of 150 MPa and elongation of 3.5%, which is mainly attributed to precipitation strengthening. In addition, corrosion properties of experimental alloys in the 3.5wt.% NaCl solution were studied by the electrochemical tests, weight loss, hydrogen evolution measurement and corrosion morphology observation. The results suggest that peak-aged alloys show reduced corrosion rates compared with the as-cast alloys, and minor additions of Ca and/or Sr improve the corrosion resistance of the Mg-4.2Zn-1.7RE-0.8Zr alloy. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy possesses the best corrosion resistance, which is mainly due to the continuous and compact barrier wall constructed by the homogeneous and continuous second phases.

     

Effect of delayed aging on mechanical properties of an Al-Cu-Mg alloy

The effect of delayed aging on mechanical properties is characteristically found in Al-Mg-Si alloys. “Delayed aging” refers to the time elapsed between solutionizing and artificial aging. Delayed aging leads to inferior properties. This effect was investigated in an Al-Cu-Mg alloy (AU2GN) of nominal composition Al-2Cu-1.5Mg-1Fe-1Ni as a function of delay. This alloy also showed a drop in mechanical properties with delay. The results are explained on the basis of Pashley’s kinetic model to qualitatively explain the evolution of a coarse precipitate structure with delay. It is found that all the results of delayed aging in the Al-Cu-Mg alloys are similar to those found in Al-Mg-Si alloys.     

时效温度对GH2132合金组织与力学性能的影响

采用光学显微镜、扫描电镜、微机控制电子万能试验机等仪器研究了620、650、680、720、750、780 ℃单级时效和720 ℃+650 ℃双级时效对GH2132合金显微组织及力学性能的影响。结果表明:双级时效的抗拉强度和剪切强度高于单级时效的抗拉强度和剪切强度,抗拉强度达到1130 MPa,剪切强度达到720 MPa。且在620~780 ℃的温度范围内进行单级时效时,随着时效温度的提高,合金的抗拉强度和剪切强度呈现先升高后降低的趋势,在720 ℃时抗拉强度达到最大值1065 MPa,剪切强度达到最大值685 MPa。     

Microstructures evolution and mechanical properties disparity in 2070 Al-Li alloy with minor Sc addition

The microstructures and mechanical properties of Al-3.35Cu-1.2Li-0.4Mg-0.4Zn-0.3Mn-0.1Zr (mass fraction, %) alloy with Sc addition or free Sc were investigated through tensile test, SEM, EPMA and TEM. The addition of 0.082% (mass fraction) Sc element leads to the formation of Cu-rich and Sc-contained nano-sized Al₃(ScZr) particles and W phase particles. The Al₃(ScZr) particles can inhibit recrystallization to a certain extent and impede recrystallized grain growth during solution treatment. It is found that W phase cannot dissolve in supersaturated solid solution during the solution heat treatment, and the Cu content in the solutionized matrix is decreased, which causes a decrease in the fraction of Cu-contained strengthening precipitates with T₁ (Al₂CuLi) and θ′ (Al₂Cu) under T8 aging condition. Due to the formation of the W phases, the small Sc addition causes a little reduction in the strength.     

时效状态对新型高强铝合金型材力学及腐蚀性能的影响

采用拉伸测试、晶间腐蚀测试、剥落腐蚀测试和透射电镜分析等方法研究了不同时效状态对新型高强铝合金型材力学和腐蚀性能的影响。结果表明,合金型材在峰时效状态下具有最高的强度,在过时效状态下具有最优的抗腐蚀性能,在欠时效状态下合金的伸长率最高。合金晶间腐蚀和剥落腐蚀敏感性由大到小的顺序为：欠时效＞峰时效＞过时效。这主要是因为过时效处理后,晶内沉淀相的大量析出提高了基体的电极电位,晶界沉淀相的不连续分布和晶界无析出带结构有效阻断了腐蚀的阳极通道。     

时效温度对含Cu抗菌双相不锈钢力学及耐蚀性能的影响

通过SEM、EDS以及拉伸试验与电化学测试等手段,研究了时效温度对含铜抗菌双相不锈钢力学及耐蚀性能的影响。结果表明,时效处理析出的富Cu相有提高抗拉强度的作用;在540~580 ℃范围内,随着时效温度升高,富铜相粗化,材料抗拉强度及塑性下降,断口由韧性断裂逐渐向解理断裂转变;在30%醋酸溶液中,富铜相体积分数越大,试样耐蚀能力越强。     

时效处理对优质GH738合金组织及力学性能的影响

采用力学性能测试与组织观察相结合的方式研究了时效温度和保温时间对优质GH738合金组织及性能的影响规律。结果表明,时效温度和时间均会对γ′相的体积分数和尺寸产生影响。当时效温度在720~800 ℃时,随着时效温度升高,合金强度下降,一次和二次γ′相分别长大30 nm和8 nm,一次γ′相体积分数增加,二次γ′相体积分数减少,时效温度为800 ℃时一次γ′相体积分数达到峰值,约为8%。当保温时间为0~48 h时,随时效时间延长,合金强度先升高后降低,两类γ′相分别长大20 nm和6 nm,一次γ′相体积分数先增后减,二次γ′相体积分数则变化相反。当保温时间为8 h时,两类γ′相体积分数分别达到峰/谷值,含量约为8%和12%。γ′相尺寸和体积分数的变化,特别是体积分数的变化,导致位错的两种强化机制作用效果不同,致使强度发生变化。     

Influence of retrogression and reaging on microstructure,mechanical properties and susceptibility to stress corrosion cracking of an Al‐Zn‐Mg alloy

The aim of the present work was to determine the influence of the retrogression and reaging (RRA) heat treatment on the correlation between microstructure, mechanical properties and susceptibility to stress corrosion cracking (SCC) of the AlZn5Mg1 alloy in dry air and sea water. The alloy received in the T6 temper was subjected to 9 different heat treatments, including retrogression at temperature 453–513 K for 600–3600 s, and reaging at temperature 363 K or 403 K for 16 h, 24 h or 48 h. The susceptibility to SCC was investigated by slow strain rate tensile tests at 10^?6 s^?1 strain rate; change in time to failure, fracture energy and reduction in area were taken into account. Generally, the heat treatment improving mechanical properties increased susceptibility to SCC. The observed effects were discussed in terms of change in microstructure, especially size and distribution of phase precipitates. The role of change in dislocation network was the most likely of no importance.     

含钪Al-Cu-Li-Zr合金的剥蚀性能及电化学阻抗谱

采用剥落腐蚀(Exfoliation corrosion,EXCO)实验和电化学阻抗测试方法,研究时效对新型含钪Al-Cu-Li-Zr合金剥蚀性能的影响。结果表明:合金在EXCO溶液中剥落腐蚀敏感性由高到低的顺序为过时效,峰时效,欠时效;合金在EXCO溶液中浸泡初期,其电化学阻抗谱由一个高频容抗弧和低频感抗弧组成,且随浸泡时间的延长,低频感抗部分逐渐减弱直至消失;一旦发生剥蚀,合金的电化学阻抗谱出现两个部分重叠的容抗弧。依据腐蚀特征和电化学原理设计了等效电路图,对合金腐蚀发展过程的电化学阻抗谱进行了拟合,拟合数据和实验结果一致。