时效工艺对2000系高强铝合金慢应变速率拉伸性能的影响

通过慢应变速率拉伸测试、金相、扫描电镜及透射电镜分析等研究了Al-3.88Cu-1.18Mg-0.31Mn铝合金在T6、T8、T3时效状态时的应力腐蚀开裂(SCC)行为。结果表明:在T6、T8及T3时效态下,合金的应力腐蚀开裂敏感性依次降低。合金应力腐蚀与晶间腐蚀具有正相关性,表现为电化学腐蚀特征,晶界与晶内电位差的大小决定了应力腐蚀开裂敏感性的高低,其与晶界及其附近区域的微观组织特征紧密相关。     

高强铝合金慢拉伸应变速率与氢脆敏感性的关系

以7085高强铝合金材料为研究对象,通过设定不同的慢拉伸应变速率,研究材料的氢致应力开裂,同时对试样断口进行扫描电子显微镜分析,初步探讨了应变速率与氢脆敏感性的关系,为高强铝合金材料氢脆敏感性评价体系的建立提供借鉴。     

钛合金慢应变速率拉伸应力腐蚀行为研究

对TA31和TC4ELI两合金分别在干燥空气、3.5% NaCl环境下进行慢应变速率拉伸试验。结合应力-应变曲线以及断口宏观、微观组织分析两种材料的应力腐蚀敏感性。结果表明:在35℃、3.5%(w,下同) NaCl溶液、应变速率为10^-6/s条件下,TC4ELI合金应力腐蚀敏感性较高,在5×10^-7/s和5×10^-6/s的应变速率下应力腐蚀敏感性较低;TA31合金在上述3种应变速率下应力腐蚀敏感性均较低;在3.5% NaCl环境中,TA31合金断口形貌较空气中试验的断口形貌无明显的变化,TC4ELI则出现较明显的解理面。     

金属圆棒试样室温下高应变速率拉伸试验浅析

在不同应变速率下对铸铁和铸铝圆棒试样进行了单轴高速拉伸试验,研究了它们的动态力学性能及断裂情况,分析了相关因素对试验的影响。结果表明:测试应变、应力的方法,试样标距长度及夹持端长度等对试验准确性和曲线振荡程度有较大影响;使用比刚度和比强度高的夹具、短标距试样、应变片测试应力、两台相机测试应变、适当增加夹持端长度可以提高试验结果的准确性。     

铝合金应力腐蚀的电化学研究

应用电化学测试法、恒载荷拉伸法和慢应变速率拉伸法研究了硬铝合金LY12 3.5 %NaCl溶液应力腐蚀体系的电化学特性。结果表明应变速率比应力对电化学特性的影响更大。应变速率为 1.13× 10 - 5/s时 ,应力腐蚀较为敏感 ;形变强化阶段力学、化学效应最为明显 ;LY12的应力腐蚀开裂是阳极溶解和氢脆共同作用的结果     

低应变速率应力腐蚀试验方法

本文叙述了用低应变速率应力腐蚀试验技术评定材料应力腐蚀开裂敏感性的方法。其内容包括:低应变速率应力腐蚀试验方法的原理、应变速度的选择、试验结果的评定以及与常规应力腐蚀开裂试验方法的比较等。试验结果表明,低应变速率应力腐蚀试验是一种比常规的恒载荷、恒变形方法更先进的应力腐蚀试验方法。     

铸锭铝合金Al-Cu-Mg-Ti高应变速率超塑性

采用常规熔铸、热处理、小挤压比挤压及轧制这一低成本并适合于工业化规模应用的路线,研制了一种具有高应变速率超塑性的铸锭铝合金Al-Cu-Mg-Ti.拉伸试验结果表明在温度为793K、初始应变速率为3.16×10-1s-1的拉伸变形条件下,其超塑伸长率为218%,流变应力为32.5MPa.断面及表面形貌SEM分析和初熔行为的DSC分析表明,该合金高应变速率超塑性变形来自于晶界滑动和位错滑移,与液相没有关系.     

应变速率对X80管线钢应力腐蚀的影响

利用慢应变速率拉伸试验研究了应变速率对X80管线钢在土壤模拟溶液中的应力腐蚀的影响。采用的模拟溶液以我国西北部碱性土壤的化学成分为基础,在不同应变速率条件下进行试验。样品断裂后利用扫描电镜对断口形貌以及断口侧面二次裂纹进行观察。研究结果表明:X80钢在1.0×10-6s-1应变速率下表现出最高的应力腐蚀敏感性。低于该应变速率下,应力腐蚀敏感性略有降低;而高于该应变速率下,应力腐蚀敏感性明显减小。不同应变速率下应力腐蚀敏感性的差异主要是由应力腐蚀过程中腐蚀和力学作用的影响程度不同造成。应变速率低于1.0×10-6s-1时,腐蚀作用影响更大,较长的腐蚀时间造成裂纹被腐蚀,裂纹扩展受到影响,因此应力腐蚀敏感性略有降低。当应变速率高于1.0×10-6s-1时,力学作用主导整个过程,形成的裂纹没有受到足够腐蚀的情况下,在力学作用下发生快速机械扩展、断裂,因此产生了明显降低的应力腐蚀行为。     

拉伸试验的速率探讨

采用夹头分离速率控制方式对：行屈服现象和无屈服现象的试样进行拉伸试验,探讨了试验过程中试样应变速率和应力速率的变化情况。试验结果表明：在不同的变形阶段试样的应变速率是不同的,弹性阶段的应变速率比设定值低很多,屈服阶段会略高,塑性变形阶段与设定值较接近。并确定在该试验条件下可将试验速率设定在1～7mm／min。     

用低应变速率方法测定919铝合金的应力腐蚀敏感性

用低应变速率方法测定了３种热处理状态的９１９铝合金的应力腐蚀敏感性，结果表明，３种状态合金的应力腐蚀敏感性顺序与在恒载荷试验中获得的结果具有很好的相关性。因而，低应变速率方法适用于９１９及其同类合金的应力腐蚀性能研究。     

电极极化对铝合金应力腐蚀断裂敏感性的影响

为了探讨极化对铝合金应力腐蚀断裂(SCC)敏感性的影响,采用慢应变速率拉伸技术研究了不同恒电位极化条件下7075T6,7075T7351,7075RRA铝合金的应力腐蚀行为.结果表明,在-1 200～-735 mV(vs SCE)电位范围内,无论是阳极极化还是阴极极化,甚至弱极化,都会增加7075铝合金在3.5% NaCl溶液中的应力腐蚀断裂敏感性,无论哪一种热处理状态的7075铝合金在极化电位下的ISSRT均明显高于腐蚀电位下的ISSRT.同时,有阴极极化时ISSRT值随电极极化增强而减小,阳极极化时ISSRT 值有随电极极化增强而增大的趋势.但不同热处理状态的7075铝合金受极化电位的影响程度不同.由此认为,阳极溶解和氢效应都是导致7075铝合金应力腐蚀开裂的重要因素,电化学保护方法并不适用于7075铝合金应力腐蚀断裂的防护.     

7075铝合金的力学与电化学交互作用

用慢应变速率拉伸(SSRT)技术研究了7075铝合金在应力腐蚀过程中的力学与电化学交互作用.结果表明,外加极化会提高7075铝合金的应力腐蚀敏感性,这种通过极化而改变铝合金表面电化学反应从而影响断裂应力的现象是一种电化学-力学效应.然而,对于不同热处理状态的7075铝合金,外加极化对敏感性的影响程度不同.增加拉伸应力,7075-RRA铝合金的阳极极化曲线略向正移,滞后环面积扩大,但并不显著.这种拉伸应力对极化曲线的影响是一种力学-电化学效应,有利于应力腐蚀裂纹的扩展.铝合金在应力腐蚀过程中的电化学作用和力学作用是交互的,彼此促进的.     

升温时效处理7075铝合金在含SRB模拟海水中的应力腐蚀行为

7系铝合金是一种可热处理强化的铝合金,通过改变热处理工艺的方法可以提高铝合金的抗应力腐蚀性能.本文研究了不同升温时效处理下,铝合金在含硫酸盐还原菌(SRB)模拟海洋溶液中的应力腐蚀行为,并通过应力-应变曲线和断口形貌,对比分析了铝合金在无菌溶液和SRB溶液中的应力腐蚀行为差异.研究表明,升温时效处理可以提高合金的自腐蚀...     

0.8设计系数用X80管线钢在近中性pH溶液中的应力腐蚀开裂行为

采用慢应变速率拉伸(SSRT)实验研究了X80管线钢及其焊缝在近中性的NS4溶液中的应力腐蚀行为与敏感性。结果表明:X80管线钢及其焊缝主要是塑性损失,且焊缝塑性损失大于母材;X80管线钢及其焊缝在空气中属于典型的韧性断裂特征,在NS4溶液中属于穿晶应力腐蚀开裂(TGSCC),在NS4溶液中母材和焊缝断口中间区域比断口边缘区域表现出更明显的脆性断裂特征。电位在大于-749.86mV时,SCC机制为阳极溶解机制,在-749.86~-839.19mV之间时为阳极溶解和氢脆混合机制,小于-839.19mV时为氢脆机制。     

Assessment of stress corrosion cracking susceptibility by a small punch test

The object of this study is to establish a new test method for evaluating stress corrosion cracking (SCC) susceptibility of high-strength steel using a small punch (SP) test and acoustic emission (AE). A miniaturized specimen (10 × 10 × 0.5 mm) is adopted for SCC evaluation. The experiments are conducted at various loading rates and at various orientations of the specimen. The cumulative average amplitude of the AE signal per unit equivalent fracture strain ( ε _qf ) increases as the SCC susceptibility increases. Through the load–displacement behaviour, the fracture energy ( E _SP ), the SEM fractographs, and the correlation between the SCC susceptibility and the AE characteristics, it is proved that the small punch test method combined with AE measurements is a useful method to evaluate the SCC susceptibility of high-strength steel.     

电子显微分析技术在奥氏体合金应力腐蚀开裂研究领域中的应用

奥氏体合金广泛应用于核电领域。应力腐蚀开裂是核电材料主要的失效形式之一,奥氏体合金的应力腐蚀开裂关系到核电站的安全运行。综述了评估应力腐蚀开裂的试样方法以及运用现代电子显微分析技术表征应力腐蚀开裂的方法。对这些电子显微分析技术的优点进行了总结,并指出未来电子显微分析技术在应力腐蚀开裂研究中的发展方向。     

Influence of Friction Stir Weld Parameters on the Corrosion Susceptibility of EN AW-7075 Weld Seam and Heat-Affected Zone

Friction stir welding enables joining of high-strength, lightweight aluminum alloys, e.g., EN-AW-7075, below the melting point by induced plastic deformation. Therefore, heat transfer into the adjacent regions beneath the weld seam is significantly reduced as compared to fusion welding processes such as laser beam welding. However, specific zones along the weld seam area are susceptible to localized corrosion due to grain growth and the precipitation of intermetallic phases. Thus, several approaches toward lowering the corrosion susceptibility of the heat-affected zone are presented. Special interest is given to increasing the plastic deformation by the use of novel multipin welding tools that eventually facilitate reduced heat input during welding as a result of substantially lower tool revolutions. The corrosion behavior is tested by means of full material immersion tests and electrochemical measurements which provide insight into the corrosion kinetics. Using pre- and postmortem microstructural analysis, the mechanisms influencing the initiation of corrosion can be identified. Supported by in-operando temperature measurements, the varied welding parameters and their interrelationships to corrosion resistance can be derived. Furthermore, recommendations on optimal welding parameters to obtain enhanced corrosion resistance can be deduced.     

Hydrogen embrittlement property of a 1700-MPa-class ultrahigh-strength tempered martensitic steel

The hydrogen embrittlement property of a prototype 1700-MPa-class ultrahigh-strength steel (NIMS17) containing hydrogen traps was evaluated using a slow strain rate test (SSRT) after cathodic hydrogen precharging, cyclic corrosion test (CCT) and atmospheric exposure. The hydrogen content in a fractured specimen was measured after SSRT by thermal desorption spectroscopy (TDS). The relationship between fracture stress and hydrogen content for the hydrogen-precharged specimens showed that the fracture stress of NIMS17 steel was higher, at a given hydrogen content, than that of conventional AISI 4135 steels with tensile strengths of 1300 and 1500 MPa. This suggests better resistance of NIMS17 steel to hydrogen embrittlement. However, hydrogen uptake to NIMS17 steel under CCT and atmospheric exposure decreased the fracture stress. This is because of the stronger hydrogen uptake to the steel containing hydrogen traps than to the AISI 4135 steels. Although NIMS17 steel has a higher strength level than AISI 4135 steel with a tensile strength of 1500 MPa, the decrease in fracture stress is similar between these steels.     

Hydrogen embrittlement property of a 1700-MPa-class ultrahigh-strength tempered martensitic steel

Abstract

The hydrogen embrittlement property of a prototype 1700-MPa-class ultrahigh-strength steel (NIMS17) containing hydrogen traps was evaluated using a slow strain rate test (SSRT) after cathodic hydrogen precharging, cyclic corrosion test (CCT) and atmospheric exposure. The hydrogen content in a fractured specimen was measured after SSRT by thermal desorption spectroscopy (TDS). The relationship between fracture stress and hydrogen content for the hydrogen-precharged specimens showed that the fracture stress of NIMS17 steel was higher, at a given hydrogen content, than that of conventional AISI 4135 steels with tensile strengths of 1300 and 1500 MPa. This suggests better resistance of NIMS17 steel to hydrogen embrittlement. However, hydrogen uptake to NIMS17 steel under CCT and atmospheric exposure decreased the fracture stress. This is because of the stronger hydrogen uptake to the steel containing hydrogen traps than to the AISI 4135 steels. Although NIMS17 steel has a higher strength level than AISI 4135 steel with a tensile strength of 1500 MPa, the decrease in fracture stress is similar between these steels.